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Pipe, flange, pipe fitting, gasket

There are many ways to classify pipes, which can be divided into metal pipes, non-metal pipes and steel lined non-metal composite pipes.

The non-metallic pipe mainly includes rubber pipe, plastic pipe, asbestos cement pipe, graphite pipe, glass steel pipe, etc. the proportion of the use of non-metallic pipe is smaller than that of metal pipe, while the steel pipe accounts for more than 80.5% of the total process pipe installation engineering in most petrochemical plants.

Steel pipe

Welded steel pipe

20200303133128 21857 - Pipe, flange, pipe fitting, gasket

Welded steel pipe, also known as seam steel pipe, is generally made of steel plate or steel strip by rolling welding.
According to the surface treatment form of steel pipe:
It can be divided into galvanized and non galvanized. The surface galvanized hair white, also known as white iron pipe or galvanized steel pipe; the surface is not galvanized, that is, ordinary welded steel pipe, also known as black iron pipe.
Galvanized welded steel pipe is commonly used for pipelines with relatively clean transmission medium requirements, such as domestic water, purified air, instrument air, etc.; non galvanized welded steel pipe can be used for conveying steam, gas, compressed air and condensate, etc.
According to the user’s requirements, welded steel pipes can be divided into two types when leaving the factory:
One is the pipe end with thread, the other is the pipe end without thread. For welded steel pipes with thread at the pipe end, the length of each steel pipe is 4-9m; for welded steel pipes without thread, the length of each steel pipe is 4-12m.
According to the thickness of pipe wall, the welded steel pipe is different:
It is divided into thin-walled steel pipe, thickened steel pipe and ordinary steel pipe. The common steel pipe is used most in the process pipeline, and its test pressure is 2.0MPa. The test pressure of thickened steel pipe is 3.0MPa.
There are many connection methods for welded steel pipes:
There are screw connection, flange connection and welding. Flange connection is divided into threaded flange connection and welding flange connection, and welding method is divided into gas welding and arc welding.

Straight seam welded steel pipe:
Most of them are manufactured at the construction site or commissioned by the processing plant, and professional steel pipe plants do not produce.
The steel plate materials are Q235A, No.10, No.20, 16Mn, 20g, etc. the specification range is nominal diameter 200-3000mm, the maximum is 4000mm, and the wall thickness is generally 4-16MM.
The length of a single pipe with a nominal diameter of 200-900mm is 6.4m; the length of a single pipe with a nominal diameter of 1000-3000mm is 4.8m.
Applicable working temperature: Q235A is – 15-300 ℃, No. 10, No. 20, 16Mn, 20g is – 40-450 ℃, all suitable for low pressure range.
Spiral seam welded steel pipe:
It is produced by steel pipe manufacturer, with Q235A and 16Mn materials.
The specification range is nominal diameter 200-700mm, wall thickness 7-10mm, and single pipe length 8-18m.
Applicable working temperature: Q235A is – 15-300 ℃, 16Mn is – 40-450 ℃, operating pressure: Q235A is 2.5MPa, 16Mn is 4MPa.
Straight seam welded steel pipe and spiral seam welded steel pipe are mainly used to transport medium with low corrosiveness at room temperature and low pressure, such as low-pressure steam, underground circulating water, gas and oil gas, etc. Spiral seam welded steel pipe has a long single pipe, which is especially suitable for long-distance pipeline.
Specification range of commonly used welded steel pipe:
Is the nominal diameter of 6-150 mm.

Seamless steel pipe

20200303133406 52134 - Pipe, flange, pipe fitting, gasket

Seamless steel pipe is round pipe with the largest consumption and the largest variety and specification in the industrial pipeline.
Basically divided into:
There are two categories of seamless steel pipes for fluid transportation: seamless steel pipes and seamless steel pipes with specificity. The former is the steel pipe commonly used in process pipeline, while the latter is the steel pipe for boiler, cracking furnace and heat exchanger.
It can be divided into:
Carbon seamless steel pipe, chromium molybdenum seamless steel pipe and stainless and acid resistant seamless steel pipe.
According to the nominal pressure, it can be divided into:
Low pressure (0 ≤ 1.0MPa), medium pressure (1.0 < 10MPa =, high pressure (≥ 10MPa).
Seamless steel pipe is commonly used in process pipeline.
The classification is as follows:
Carbon seamless steel pipe
The commonly used manufacturing materials are No. 10, No. 20 and 16Mn steel.
The specification range is: hot rolled outer diameter φ 32-630mm, cold drawn outer diameter φ 6-200mm, single pipe length 4-12m, allowable operating temperature – 40-450 ℃.
It is widely used to transport various non corrosive media, such as steam, oxygen, compressed air, oil and oil gas.
❷ Low alloy steel seamless steel pipe
It refers to the alloy steel pipe containing a certain proportion of alloy elements.
There are usually two types:
One is low alloy steel pipe containing manganese element, which is called ordinary low alloy steel pipe, such as 16Mn, 15MnV, etc.; the other is low alloy steel pipe containing chromium, molybdenum and other elements, which is called chromium molybdenum steel pipe.
Commonly used are 12CrMo, 15CrMo, 12cr2mo, 1Cr5Mo, etc. the specification range is φ 10-φ 273mm in outer diameter, 4-12m in single pipe length, and – 40-550 ℃ in chrome molybdenum steel pipe.
Low alloy seamless steel pipe is mainly used to transport various high temperature oil products, oil and gas, salt water with low corrosiveness, low concentration organic acid, etc.
❸ Stainless acid resistant seamless steel pipe
According to the different contents of chromium, nickel and titanium, there are many varieties, including Cr13, 00Cr17Ni14Mo2, 1cr18ni12mo2ti, 1Cr18Ni9Ti, etc.
Among these steel grades, 1Cr18Ni9Ti is the most used, which is usually represented by simplified material code 18-8 on the construction drawing, and the applicable temperature range is – 196 ~ 700 ℃.
It is used to transport various corrosive media in chemical production, such as nitric acid, acetic acid and urea.
❹ High pressure seamless steel pipe
Its manufacturing material is basically the same as the above seamless steel pipe, except that the pipe wall is thicker than the medium and low pressure seamless steel pipe, and the thickest pipe wall is up to 40 mm.
For example, the specification of high-pressure seamless steel pipe for fertilizer equipment is φ 14 × 4 (mm) – 273 × 40 (mm), the length of single pipe is 4-12m, the applicable pressure range is 10-32mpa, and the working temperature is – 40-400 ℃.
In the petrochemical plant, the above high-pressure seamless steel pipe is used to transport feed gas, hydrogen nitrogen, synthetic gas, water vapor, high-pressure condensate and other media.
❺ Low temperature steel pipe
In the cold zone of the imported project, the amount of cold zone is more, the material grades are stpl-39 and stpl-46, and the working temperature can reach – 105 ℃.
Low temperature steel pipe is divided into seamless steel pipe and seamed steel pipe. The nominal diameter of seamless low temperature steel pipe is 15-400mm, and the wall thickness is the same as that of carbon steel pipe. The nominal diameter of seamed low temperature steel pipe is 400-1100mm, the wall thickness is 6-10mm, and the standard length of single pipe is 6m.
It is suitable for conveying all kinds of non corrosive low-temperature medium pipes. At present, there is no batch production of steel pipes corresponding to this standard in China.

Copper tube

20200303134342 15860 - Pipe, flange, pipe fitting, gasket

There are two kinds of copper tubes: copper tube and brass tube:

  • The materials used for manufacturing copper tubes are T2, T3, T4 and tup, with a high copper content, accounting for more than 99.7%;
  • The grades of brass tubes are H62, H68, etc., which are all zinc and copper alloys. For example, H62 brass tubes are composed of 60.5% – 63.5% copper, 39.6% zinc and less than 0.5% other impurities.

There are two manufacturing methods of copper pipe: drawing and extrusion:

  • The outer diameter of drawn copper pipe is φ 3-φ 200mm, the outer diameter of extruded copper pipe is φ 32-φ 280mm, and the wall thickness is 1.5-5mm;
  • The specification range of copper tube for copper plate rolling welding is φ 155-φ 505mm, and there are two supply modes: single tube and coiled tube.

The suitable working temperature of copper pipe is below 250 ℃, which is mainly used in oil pipeline, heat preservation tracing pipe and air separation oxygen pipeline.

Titanium tube

20200303134857 98673 - Pipe, flange, pipe fitting, gasket

Titanium pipe is a new kind of pipe in recent years. Because it has the characteristics of light weight, high strength, strong corrosion resistance and low temperature resistance, it is often used in the process parts that other pipes are not competent.
Titanium tube is made of TA1 and TA2 industrial pure titanium, and its applicable temperature range is – 140 ~ 250 ℃. When the temperature exceeds 250 ℃, its mechanical properties will decline.
The specification range of commonly used titanium pipe is 20-400mm nominal diameter. It is suitable for low and medium pressure pipes with a wall thickness of 2.8-12.7mm and a wall thickness of 3.7-21.4mm.
Although titanium tube has many advantages, it has not been widely used because of its high price and difficult welding.

Materials for Pipe

Chemical Composition

Maximum values in % Type S
(Seamless)
Type E
(ERW)
Type F
(Furnace Weld)
A53 Pipe Grade–> Grade A Grade B Grade A Grade B Grade A
Carbon 0.25 0.3 0.25 0.3 0.3
Manganese 0.95 1.2 0.95 1.2 1.2
Phosphorous 0.05 0.05 0.05 0.05 0.05
Sulfur 0.045 0.045 0.045 0.045 0.045
Copper 0.4 0.4 0.4 0.4 0.4
Nickel 0.4 0.4 0.4 0.4 0.4
Chromium 0.4 0.4 0.4 0.4 0.4
Molybdenum 0.15 0.15 0.15 0.15 0.15
Vanadium 0.08 0.08 0.08 0.08 0.08
seamless carbon steel pipe – chemical composition, %
Element C
max
Mn P
max
S
max
Si
min
Cr
max (3)
Cu
max (3)
Mo
max (3)
Ni
max (3)
V
max (3)
ASTM A106 Grade A 0.25 (1) 0.27-0.93 0.035 0.035 0.10 0.40 0.40 0.15 0.40 0.08
ASTM A106 Grade B 0.30 (2) 0.29-1.06 0.035 0.035 0.10 0.40 0.40 0.15 0.40 0.08
ASTM A106 Grade C 0.35 (2) 0.29-1.06 0.035 0.035 0.10 0.40 0.40 0.15 0.40 0.08

SS Pipes Grade

UNS

C

Mn

P

S

Si

Cr

Ni

Mo

Ti

Nb

N

TP304

S3040

0.08

2.0

0.045

0.030

1.0

18.0-20.0

8.0-11.0

 

 

 

 

TP304L

S30403

0.035

2.0

0.045

0.030

1.0

18.0-20.0

8.0-13.0

 

 

 

 

TP304H

S30409

0.04-0.10

2.0

0.045

0.030

1.0

18.0-20.0

8.0-11.0

 

 

 

 

TP304N

S30451

0.08

2.0

0.045

0.030

1.0

18.0-20.0

8.0-18.0

 

 

 

0.10-0.16

TP304LN

S30453

0.035

2.0

0.045

0.030

1.0

18.0-20.0

8.0-12.0

 

 

 

0.10-0.16

TP309S

S30908

0.08

2.0

0.045

0.030

1.0

22.0-24.0

12.0-15.0

0.75

 

 

 

TP309H

S30909

0.04-0.10

2.0

0.045

0.030

1.0

22.0-24.0

12.0-15.0

 

 

 

 

TP309Cb

S30940

0.08

2.0

0.045

0.030

1.0

22.0-24.0

12.0-16.0

0.75

 

10xC min
1.10 max

 

TP309HCb

S30941

0.04-0.10

2.0

0.045

0.030

1.0

22.0-24.0

12.0-16.0

0.75

 

10xC min
1.10 max

 

TP310S

S3108

0.08

2.0

0.045

0.030

1.0

24.0-26.0

19.0-22.0

0.75

 

 

 

TP310H

S3109

0.04-0.10

2.0

0.045

0.030

1.0

24.0-26.0

19.0-22.0

 

 

 

 

TP310Cb

S31040

0.08

2.0

0.045

0.030

1.0

24.0-26.0

19.0-22.0

0.75

 

10xC min
1.10 max

 

TP310HCb

S31041

0.04-0.10

2.0

0.045

0.030

1.0

24.0-26.0

19.0-22.0

0.75

 

10xC min
1.10 max

 

TP316

S3160

0.08

2.0

0.045

0.030

1.0

16.0-18.0

11.0-14.0

2.0-3.0

 

 

 

TP316L

S31603

0.035

2.0

0.045

0.030

1.0

16.0-18.0

10.0-14.0

2.0-3.0

 

 

 

TP316H

S31609

0.04-0.10

2.0

0.045

0.030

1.0

16.0-18.0

11.0-14.0

2.0-3.0

 

 

 

TP316Ti

S31635

0.08

2.0

0.045

0.030

0.75

16.0-18.0

10.0-14.0

2.0-3.0

5x
(C-N)
-0.70

 

0.10

TP316N

S31651

0.08

2.0

0.045

0.030

1.0

16.0-18.0

10.0-14.0

2.0-3.0

 

 

0.10-0.16

TP316LN

S31653

0.035

2.0

0.045

0.030

1.0

16.0-18.0

11.0-14.0

2.0-3.0

 

 

0.10-0.16

TP317

S3170

0.08

2.0

0.045

0.030

1.0

18.0-20.0

10.0-14.0

3.0-4.0

 

 

 

TP317L

S31703

0.035

2.0

0.045

0.030

1.0

18.0-20.0

11.0-15.0

3.0-4.0

 

 

 

TP321

S3210

0.08

2.0

0.045

0.030

1.0

17.0-19.0

9.0-12.0

 

 

 

0.10

TP321H

S32109

0.04-0.10

2.0

0.045

0.030

1.0

17.0-19.0

9.0-12.0

 

 

 

0.10

TP347

S3470

0.08

2.0

0.045

0.030

1.0

17.0-19.0

9.0-13.0

 

 

 

 

TP347H

S34709

0.04-0.10

2.0

0.045

0.030

1.0

17.0-19.0

9.0-13.0

 

 

 

 

TP347LN

S34751

0.05-0.02

2.0

0.045

0.030

1.0

17.0-19.0

9.0-13.0

 

 

0.20-
50.0

0.06-0.10

TP348

S3480

0.08

2.0

0.045

0.030

1.0

17.0-19.0

9.0-13.0

 

 

 

 

TP348H

S34809

0.04-0.10

2.0

0.045

0.030

1.0

17.0-19.0

9.0-13.0

 

 

 

ASTM A335
Low-Alloy Steel
(Grades)
UNS
equivalent
C≤ Mn P≤ S≤ Si≤ Cr Mo
P1 K11522 0.10~0.20 0.30~0.80 0.025 0.025 0.10~0.50 0.44~0.65
P2 K11547 0.10~0.20 0.30~0.61 0.025 0.025 0.10~0.30 0.50~0.81 0.44~0.65
P5 K41545 0.15 0.30~0.60 0.025 0.025 0.5 4.00~6.00 0.44~0.65
P5b K51545 0.15 0.30~0.60 0.025 0.025 1.00~2.00 4.00~6.00 0.44~0.65
P5c K41245 0.12 0.30~0.60 0.025 0.025 0.5 4.00~6.00 0.44~0.65
P9 S50400 0.15 0.30~0.60 0.025 0.025 0.50~1.00 8.00~10.00 0.44~0.65
P11 K11597 0.05~0.15 0.30~0.61 0.025 0.025 0.50~1.00 1.00~1.50 0.44~0.65
P12 K11562 0.05~0.15 0.30~0.60 0.025 0.025 0.5 0.80~1.25 0.44~0.65
P15 K11578 0.05~0.15 0.30~0.60 0.025 0.025 1.15~1.65 0.44~0.65
P21 K31545 0.05~0.15 0.30~0.60 0.025 0.025 0.5 2.65~3.35 0.80~1.60
P22 K21590 0.05~0.15 0.30~0.60 0.025 0.025 0.5 1.90~2.60 0.87~1.13
P91 K91560 0.08~0.12 0.30~0.60 0.02 0.01 0.20~0.50 8.00~9.50 0.85~1.05
P92 K92460 0.07~0.13 0.30~0.60 0.02 0.01 0.5 8.50~9.50 0.30~0.60
Grade C Mn Si P S Cr Mo Ni N Fe
S31803 0.030 max 2.00 max 1.00 max 0.030 max 0.020 max 22.0 – 23.0 3.0 – 3.5 4.50 – 6.50 0.14 – 0.20 63.72 min
S32205 0.030 max 2.00 max 1.00 max 0.030 max 0.020 max 21.0 – 23.0 2.50 – 3.50 4.50 – 6.50 0.8 – 0.20 63.54 min
Grade C Mn Si P S Cr Mo Ni N Fe
S 32750 0.030 max 1.20 max 0.80 max 0.035 max 0.020 max 24.00 – 26.00 3.00 – 5.00 6.00 – 8.00 0.24 – 0.32 58.095 min
S 32760 0.05 max 1.00 max 1.00 max 0.030 max 0.010 max 24.00 – 26.00 3.00 – 4.00 6.00 – 8.00 0.20 – 0.30 57.61 min
Fe C Ni Cr Mo Co Cu Mn S Si W V P Al Ti
Nickel 200 .40 max .15 max 99.0 min .25 max .35 max .01 max .35 max
Nickel 201 .40 max .02 max 99.0 min .25 max .35 max .01 max .35 max
Hastelloy C276 4.0-7.0 .01 max Remainder 14.5-16.5 15.0-17.0 2.5 max 1.0 max .03 max .08 max 3.0-4.5 .35 max .04 max
Inconel 600 6.0-10.0 .15 max 72.0 min* 14.0-17.0 .50 max 1.00 max .015 max .50 max
Inconel 601 14 0.05 61.5 22.5 0.3 0.2 1.4
Inconel 625 5.0 max .10 max Remainder 20.00-30.00 8.0-10.0 1.0 max** .50 max .015 max .50 max .015 max .40 max .40 max
Inconel 718 Remainder .08 max 50.00-55.00 17.00-21.00 2.80-3.30 1.00 max .30 max .35 max .015 max .35 max .015 max .20-.80 .65-1.15
Incoloy 800 39.5 min .10 max 30.0-35.0 19.0-23.0 .15-.60 .15-.60
Incoloy 800H 39.5 min .05-.10 30.0-35.0 19.0-23.0 .15-.60 .15-.60
Incoloy 800HT 39.5 min .06-.10 30.0-35.0 19.0-23.0 .25-.60 .25-.60
Incoloy 825 22.0 min 0.05 max 38.0-46.0 19.5-23.5 1.5-3.0 1.0 max 0.03 max 0.5 max 0.2 max .6-1.2
Alloy 20 Balance .07max 32.00-38.00 19.0-21.0 2.0-3.0 3.0-4.0 2.0max .035max 1.0max .045max
Monel K500 2.0 max .25 max 63.0-70.0 Remainder 1.5 max .01 max .50 max 2.30-3.15 .35-.85

Mechanical Properties

Seamless and ERW A53 Grade A A53 Grade B
Tensile Strength, min, psi 48,000 60,000
Yield Strength 30,000 35,000
ASTM A106 pipe A106 Grade A A106 Grade B A106 Grade C
Tensile Strength, min., psi 48,000 60,000 70,000
Yield Strength, min., psi 30,000 35,000 40,000
SS Pipes Grade
ASTM A312/ASME SA312
Tensile Strength
N/mm2 (min)
Yield Strength
N/mm2 (min)
Elongation
% (min)
TP304 515 205 35
TP304L 485 170 35
TP316 515 205 35
TP316L 485 170 35
TP321 OD < 17,1 mm – 515; OD < 17,1 mm – 205; 35
OD > 17,1 mm – 485 OD > 17,1 mm – 170


 

 

 

Hardness

A335 Low-Alloy Pipe

UNS Number

Yield Strength ksi

Tensile Strength ksi

Elongation %

Rockwell

Brinell

P1

K11522

30

55

30

P2

K11547

30

55

30

P5

K41545

40

70

30

207 max

P9

S50400

30

60

30

P11

K11597

30

60

20

P12

K11562

32

60

30

174 max

P22

K21590

30

60

30

P91

K91560

60

85

20

Grades Density (g/cm 3) Density (lb/in 3) Melting Point (°C) Melting Point (°F)
S31803 / S32205 7.805 0.285 1420 – 1465 2588 – 2669
Grades Density (g/cm 3) Density (lb/in 3) Melting Point (°C) Melting Point (°F)
S32750 / S32760 7.8 0.281 1350 2460

Physical Properties

Density at 20 °C
Kg/dm³
Modulus of elasticity kN/mm² at Thermal conductivity at 20 
W/m K
Spec. thermal capacity at 20 
J/kg K
Spec. electrical resistivity at 20 °C
Ω mm²/m
20  300 C° 400  450 
7,85 210 192 184 179 51 461 0,20
ASTM A106 pipe A106 Grade A A106 Grade B A106 Grade C
Tensile Strength, min., psi 48,000 60,000 70,000
Yield Strength, min., psi 30,000 35,000 40,000

Testing Requirements

Test ASTM A53 Grade A ASTM A53  Grade B
Yield  30,000 psi 35,000 psi
Tensile 48,000 psi 60,000 psi
Elongation Determined by formula Determined by formula

Pipe diameter tolerance

NPS OD Tolerance
+
inch mm inch mm
1/8 to 1 1 /2
> 1 1 /2 to 4
> 4 to 8
> 8 to 18
> 18 to 26
> 26 to 34
> 34 to 48
1/64(0.015)
1/32(0.031)
1/16(0.062)
3/32(0.093)
1/8(0.125)
5/32(0.156)
3/16(0.187)
0.4
0.8
1.6
2.4
3.2
4.0
4.8
1/32(0.031)
1/32(0.031)
1/32(0.031)
1/32(0.031)
1/32(0.031)
1/32(0.031)
1/32(0.031)
0.8
0.8
0.8
0.8
0.8
0.8
0.8

Pipe wall thickness tolerance

The nominal wall thickness tolerance is +/- 12.5%.

NPS WT Tolerance, %
+
1/8-2 1 /2 20.0 12.5
3~18, t/D≤ 5% 22.5 12.5
3~18, t/D> 5% 15.0 12.5
≥ 20, welded 17.5 12.5
≥ 20, seamless, t/D≤ 5% 22.5 12.5
≥ 20, seamless, t/D> 5% 15.0 12.5

Pipe finishing and testing

Polishing Manufacturers can polish any stainless steel pipe item to a #4 polish, #6 Polish, #7 polish or a #8 mirror finish.
Cuttings Stainless steel pipes can be produced in standard lengths or cut to size (standard lengths are 20′ and 40′ depending on the nominal pipe size).
Beveling Manufacturers can bevel the edges of stainless steel pipes to prepare them for welding.
Threading Stainless steel pipes can be supplied, besides plain and beveled ends, also with threaded ends (generally for NPS below 2 inches)
Pipe Honing & Turning Manufacturers can hone SS pipe and tube, using precision abrasion tools and obtain any desired finish or dimensional tolerance.
Heat treating & Annealing Most stainless steel pipes grades can be heat treated to modify their mechanical properties.
Positive Material Identification (PMI) Manufacturers can perform PMI testing to ascertain the actual content of Nickel, Chrome, and Moly in the pipe.
UT Testing In some cases, UT testing of the stainless steel plates may be required.

Flanges

The type of flange to be used for a piping application depends, mainly, on the required strength for the flanged joint. Flanges are used, alternatively to welded connections, to facilitate maintenance operations (a flanged joint can be dismantled quickly and conveniently).

Let’s now dive in, showing the key types of flanges with pictures.

WELDING NECK FLANGE

stainless steel weld neck flange 300x244 - Pipe, flange, pipe fitting, gasket .    weld neck flange - Pipe, flange, pipe fitting, gasket

A welding neck flange (“WN”)features a long tapered hub that can be welded with a pipe.

This flange type is used, normally, in high-pressure and high/low temperatures applications that require an unrestricted flow of the fluid conveyed by the piping system (the bore of the flange matches with the bore of the pipe).

The absence of pressure drops prevents negative effects as turbulence and erosion/corrosion of the metals in the proximity of the flanged joints.

The tapered hub allows a smooth distribution of the mechanical stress between the pipe and the weld neck flange and facilitates the execution of radiographic inspections to detect possible leakages and welding defects.

The dimension of the flange (NPS and the pipe schedule) shall match the dimension of the connecting pipe.

A welding neck flange is connected to a pipe by a single full penetration V-shaped butt weld.

LONG WELDING NECK

long weld neck flange - Pipe, flange, pipe fitting, gasket

Long weld neck flanges (“LWN”) are similar to weld neck flanges, with the exception that the neck (tapered hub) is extended and acts like a boring extension.

Long weld neck flanges are generally used on vessels, columns or barrels. These flange types are available also in the heavy barrel (HB) and equal barrel (E) types.

SLIP ON FLANGE

slip on flange - Pipe, flange, pipe fitting, gasket     slip on flange - Pipe, flange, pipe fitting, gasket

A slip-on flange is connected to the pipe or the fittings by two fillet welds, one executed inside and one outside the cavity of the flange.

The bore size of a slip-on flange is larger than the outside diameter of the connecting pipe, as the pipe has to slide inside the flange to be connected by the execution of a fillet weld.

Slip-on flanges are also defined “Hubbed Flanges” and they are easy to recognize due to their slim and compact shape.

Weld neck vs slip on flange

Flanged joints made with slip-on flanges are, in the long run, a bit more fragile than connections made with welding neck flanges (in similar service conditions). This seems due to the following facts:

  • a welding neck flange features a tapered hub, absent in a socket weld flange, which distributes the mechanical stress between the pipe and the flange more evenly
  • a welding neck joint as only one welding area instead of two (socket weld flange).

Another advantage of the welding neck flange is that it can be connected either to pipes and fittings, whereas socket weld flanges suit pipes only.

THREADED FLANGE

threaded flange - Pipe, flange, pipe fitting, gasket      threaded flange - Pipe, flange, pipe fitting, gasket

Threaded flanges are joined to pipes by screwing the pipe (which has a male thread, generally NPT per ASME B1.20.1) onto the flange, without seam welds (in certain cases, though, small welds are applied to increase the strength of the connection).

Threaded flanges are available in sizes up to 4 inches and multiple pressure ratings, however, they are used, mostly, small size piping in low pressure and low-temperature applications, like water and air utility services.

Threaded flanges are also a mandatory requirement in explosive areas, such as gas stations and plants, as the execution of welded connections in such environments would be dangerous.

SOCKET WELD FLANGE

socket weld flange - Pipe, flange, pipe fitting, gasket .        socket weld flange - Pipe, flange, pipe fitting, gasket

Socket weld flanges are connected to pipes using a single fillet weld executed on the outer side of the flange (different from the slip-on flange type that requires two welds).

According to ASME B31.1, to execute a flanged connection using a socket weld flange, the pipe shall be at first inserted in the socket of the flange until it reaches the bottom of the flange, then it should be lifted by 1.6 mm and finally welded.

This gap shall be left to allow proper positioning of the pipe inside the flange socket after the solidification of the weld.

Socket Weld Flanges are used for small-size and high-pressure piping that do not transfer highly corrosive fluids.

This due to the fact that these flange types are subject to corrosion in the gap area between the end of the pipe and the shoulder of the socket.

Their static strength of socket weld flanges is similar to slip-on flanges, but their fatigue strength is higher due to the presence of a single, instead of double, fillet weld.

LAP JOINT FLANGE

laop joint flange - Pipe, flange, pipe fitting, gasket lapjoint and stub end - Pipe, flange, pipe fitting, gasket

Lap joint flanges feature a flat face and are always used in conjunction with a stub end.

Lap joint flanges resemble, in shape, slip-on flanges except for the radius at the crossing of the flange face and the bore to accommodate the flanged portion of the stub end.

A lap joint flange slips over the pipe and seats on the back of the stub end and the two are kept together by the pressure of the bolts.

The use of lap joint flanges in combination with stub ends is a cost-effective solution for stainless steel or nickel alloy pipelines, as the material of the lap joint flange can be of a lower grade (generally carbon steel) than the material of the stub end (which has to match the pipe grade, as in contact with the conveyed fluid).

This arrangement, therefore, has these two advantages:

  1. Reduces the overall cost of the pipeline’s flanged joints, as the use of higher grade materials is minimized;
  2. Bolting operations are simplified, as the lap joint flange can be rotated around the pipe to help with bolts alignment.

BLIND FLANGE

blind flange - Pipe, flange, pipe fitting, gasket

Contrary to all the flange types seen above, blind flanges do not have a center hole, and are used to blind or seal a pipeline, a valve/pressure vessel and block the flow of the fluid.
Blind flanges have to withstand remarkable mechanical stress due to the system pressure and the required bolting forces.
Blind flanges allow easy access to the pipeline, as they can be easily unbolted to let the operator execute activities inside the terminal end of the pipe (this is also the reason why the blind flange type is used as manhole for pressure vessels, at times).
It is maybe interesting to observe that, while this flanges type is easier to manufacture, they are sold at a premium average cost per kilogram compared to the other flange types.

Special types of flanges

NIPOFLANGE

Nipoflange1 - Pipe, flange, pipe fitting, gasket

Nipoflange

A Nipoflange is used for branch pipelines at 90 degrees and is a product manufactured by combining a welding neck flange with a forged Nipolet.

However, a Nipoflange is a solid single piece of forged steel and not two different products welded together.

To install a Nipoflange, the piping staff has to weld the Nipolet part of the device on the run pipe and bolt the flanged part on the flange of the branched pipe.

Nipoflanges are available in different materials, such as carbon steel ASTM A105 (high-temperature service), ASTM A350 (low-temperature carbon steel), ASTM A182 (stainless steel grades, including duplex and super duplex) and nickel alloys (Inconel, Incoloy, Hastelloy, etc).

Nipoflanges are also manufactured in the reinforced variant, which has additional mechanical strength compared to a standard Nipoflange.

WELDOFLANGE

weldoflange2 - Pipe, flange, pipe fitting, gasket

Weldoflange

A Weldoflange is conceptually similar to a Nipoflange, as that they are a combination of a weld neck flange and a branch fitting connection (a Weldolet in this case). Weldoflanges are made out of a single piece of solid forged steel, not by welding separate parts together.

ELBOFLANGE AND LATROFLANGE

Other less common types of flange Olets is the so-called Elboflange (a combination of a flange and an Elbolet) and “Latroflange” (combination of a flange with a Latrolet). Elboflanges are used to branch a pipeline at 45 degrees.

elbowflange - Pipe, flange, pipe fitting, gasket

Elboflange

SWIVEL FLANGE

Swivel ring flanges facilitate the alignment of the bolt holes between the two mating flanges, a feature that is helpful in many circumstances, such as the installation of large diameter pipelines, subsea and offshore pipelines, pipe works in shallow waters and similar environments.Swivel flanges suit oil, gas, hydrocarbons, water, chemical and other demanding fluids in petrochemical and water management applications.

In the case of a large diameter pipeline, for instance, the pipe is fitted, at one end, with a standard welding neck flange, and with a swivel flange at the other end: by simply rotating the swivel flange on the pipe, the operators can achieve a perfect alignment of the bolt holes in a way easier and faster way.

The major standards for swivel ring flanges are ASME/ANSI, DIN, BS, EN, ISO, etc. The most common standard for petrochemical application is the ANSI/ASME B16.5 or ASME B16.47.

Swivel flange - Pipe, flange, pipe fitting, gasket

Swivel flange

Swivel flanges are available in all the standard shapes of common flanges, i.e. weld-neck, slip-on, lap-joint, socket weld etc, in all material grades and in a wide dimensional range (sizes can vary from 3/8” to 60” and pressure ratingfrom 150 to 2500).

Swivel flanges can be manufactured in carbon steel (ASTM A105), alloy steel (ASTM A182 F1, A182 F5, A182 F9, A182 F91), and, stainless steel (ASTM A182 F304, A182 F304L, A182 F316, A182 F316L).

EXPANDING FLANGE (“EXPANDER”)

expander flange - Pipe, flange, pipe fitting, gasket

Expander flange

Expanding flanges, or “expander flanges”, are used to increase the bore of the pipeline from a specific point to another or to connect pipes to other mechanical devices such as pumps, compressors, and valves that have different inlets sizes.

The expanding flange represented in the picture is a welding neck flange with a larger bore on the non-flanged end.

Expanding flanges can be used to increase the run pipe bore only by one or maximum two sizes and not more (example: from 2 to 3 or maximum 4 inches).

Expander flanges are a cheaper (and lighter) solution compared to the combination of a buttweld reducer and a standard flange (which is the standard solution for pipe bore increases above 2 sizes).

The most common materials for expanding flanges are A105 (high-temp. carbon steel), A350 (LTCS) and ASTM A182 (stainless steel and above).
Pressure ratings and dimensions of expanding flanges are in accordance with the ANSI/ASME B16.5 specification and are available with raised or flat face (RF, FF).

expanding flange - Pipe, flange, pipe fitting, gasket
The drawing of an ASME expanding flange.

Reducing flange (“reducer”)

reducer flange - Pipe, flange, pipe fitting, gasket

Reducer flange

Reducing flanges, otherwise called reducer flanges, have an opposite function than expander flanges seen above, i.e. they are used to decrease the bore of a pipeline.

The bore of the run pipe can be safely reduced by only 1 or 2 sizes (otherwise a solution based on the combination of a butt weld reducer and a standard flange has to be used).

Reducing flanges are available in most sizes and material grades, and are not generally available from stock.

Reducing flanges follow the same considerations in terms of specifications, sizes and material grades as expander flanges.

Types of flange face

The ASME B16.5 and ASME B16.47 norms mention a few different types of flange faces:

  • Flat face flange (FF)
  • Raised face flange (RF)
  • Ring joint flange (RTJ)
  • Lap joint flange
  • Male and female flange (M&F)
  • Large and small tongue-and-groove flange (T&G)

flange face - Pipe, flange, pipe fitting, gasket
Let’s take a closer look at the different types of flange faces, RF, FF, lap joint, ring joint, grooved:

Raised face flange (RF)

    RF flange finish - Pipe, flange, pipe fitting, gasket

A raised face flange (RF) is easy to recognize as the gasket surface area is positioned above the bolting line of the flange.

A raised face flange is compatible with a wide range of flange gaskets, ranging from flat to semi-metallic and metallic types (as, for example, jacketed gaskets and spiral wound gaskets), either ring or full face.

The main scope of a raised face flange design is to concentrate the pressure of the two mating flanges on a small surface and increase the strength of the seal.

The height of the raised face depends on the flange pressure rating as defined by the ASME B16.5 specification (for pressure classes 150 and 300, the height is 1.6 mm or 1/16 inch, for classes from 400 to 2500, the raised face height is approximately 6.4 mm, or 1/4 inch).

The most common flange finish for ASME B16.5 RF flanges is 125 to 250 micron Ra (3 to 6 micron Ra). The raised face is, according to ASME B16.5, the default flange face finish for manufacturers (this means that buyer shall specify in the order if another flange face is required, as flat face or ring joint).

Raised face flanges are the most sold type of flange, at least for petrochemical applications.

raised face flange - Pipe, flange, pipe fitting, gasket

Flat face flange (FF)

     Flate face flange - Pipe, flange, pipe fitting, gasket

Flat face flanges (FF) have a contact surface having the same height as the bolting line of the flange. Full face gaskets, generally of the soft type, are used between two flat face flanges.

According to ASME B31.3, a flat face flange should never be mated with a raised face flange as the resulting flanged joint would definitely leak.

     Ring joint flange - Pipe, flange, pipe fitting, gasket

A ring joint flanges (RTJ) is used when a metal-to-metal seal between the mating flanges is required (which is a condition for high-pressure and high-temperature applications, i.e. above 700/800 C°).

A ring joint flange features a circular groove to accommodate a ring joint gasket (oval, or rectangular).

As the two ring joint flanges are bolted together and then tightened, the applied bolting force deforms the gaskets inside the flange groove creating a very tight metal-to-metal seal. To make this happen, the material of the ring joint gasket has to be softer (more ductile) than the material of the flange.

RTJ flanges can be sealed by RTJ gaskets of different styles (R, RX, BX) and profiles (example: octagonal/oval for the R style).

The most common RTJ gasket is the R style with an octagonal section, as it ensures a very strong seal (the oval section is an older type). A “flat groove” design, however, accepts both RTJ gaskets having an octagonal or oval section.

Ring Joint flange - Pipe, flange, pipe fitting, gasket

LAP JOINT FLANGE

A lap joint flange has a flat face, which is not used to seal the flanged joint but simply hosts the back of a stub end. The sealing surface is actually on the stub end itself and may be either flat face or raised face.

lap joint and stub ends - Pipe, flange, pipe fitting, gasket

Tongue and groove flange (T and G)

     Tongue and groove flange - Pipe, flange, pipe fitting, gasket

Two tongue and groove flanges (T&G face) perfectly fit one into the other: one flange has a raised ring, the other a groove and they can be mated easily (the tongue enters the groove and seals the joint).

Tongue and groove flanges are standardized in both large and small types.

Male and female flange (M and F)

Male and female flange face finish - Pipe, flange, pipe fitting, gasket

Similarly to tongue and groove flanges, male and female flanges (M&F face type) match one to the other as well.

One flange has an area extended beyond its face area, the male flange, the other flange has a matching depression machined on the facing surface, the female flange.

The female face is 3/16” deep, while the male face is 1/4″ high, and both of them are smooth finished.

The outer diameter of the female face retains the gasket.

Flange face finish

To ensure that a flange mates with the gasket and the companion flange perfectly, some roughness is required on the flange surface area (RF and FF flange finish only). The type of roughness on the flange face surface defines the type of “flange face finish”.

Common types are stock, concentric serrated, spiral serrated and smooth flange finish.

Steel flanges are available with four basic face finish, however, the common objective of any type of flange face finish is to create the desired roughness on the face of a flange to ensure a strong match between the flange, the gasket, and the mating flange and thus provide a high-quality seal.

flange face finish - Pipe, flange, pipe fitting, gasket

Source: Officine Orsi, Italy

Let’s now dive into the most common flange face finish types:

Stock finish

The stock finish is the most widespread type of finish as it suits the large majority of applications. The pressure embeds the soft face of the gasket into the flange finish and results in the formation of a good seal due to the friction existing between the contacting parts.

As the mating flanges are bolted together, gaskets get “squeezed” into the flange face surface and create a very tight seal.

A stock finish face is manufactured using a phonographic spiral groove featuring a 1.6mm radius round-nose tool with a depth of 0.15mm and a feed-rate of 0.8mm per revolution. The resulting “Ra” value (AARH) for the surface ranges from 125µinch to 500 µinch (125 µm to 12.5 µm).

Spiral serrated

Spiral serrated finish is a phonographic spiral groove type that differs from the stock finish as the groove is crafted by a 90 degrees tool (instead of a round nosed one) that creates a “V” geometry with a 45-degree serration angle.

A serrated finish, concentric or spiral, has from 30 to 55 grooves per inch and roughness between 125 to 250 µinch.

Concentric serrated

The concentric serrated flange finish features concentric grooves instead of spirals.

The grooves are crafted by the same 90-degree tool used for the spiral serrated finish, but the serrations have an even design on the face of the flange. To have concentric grooves, the tool has a feed rate of 0.039mm per revolution and a depth of 0.079mm.

Smooth finish or face

Flanges with a smooth finish do not show visible tool markings at naked eye.

This type of flange finish is used with metal-facing gaskets such as the jacketed type.

As per the stock finish, this is achieved by having the contact surface machined with a continuous spiral groove generated by a 0.8mm radius round-nosed tool at a feed rate of 0.3mm per revolution with a depth of 0.05mm (that creates a roughness between Ra 3.2 and 6.3 micrometers, i.e. 125 – 250 microinches).

Coldwater finish

The cold water finishes appear shiny to the naked eye and very smooth. The AARH value for these surfaces ranges between 85 µinch to 100 µinch. They are used with metal to metal seals (no gasket).

flange face finish - Pipe, flange, pipe fitting, gasket

What is AARH?

The term AARH (“arithmetic average roughness height”) refers to the flange face smoothness/roughness. The average arithmetic roughness height values are very important during the selection of flanges and gasket materials. Higher the “Ra” values depict a more rough surface, while lower values represent the smoother surface.

Every material possesses a surface roughness and sometimes surfaces are finished deliberately to have a specific roughness (small or bigger).

The “Arithmetic Average Roughness Height” (AARH) is the common indicator to measure the roughness of a surface, and it is the average height of the irregularities on the metal surface, from the mean line as shown in the following figure.

The symbol Y1 to Y8 represent the peak heights which are measured from the mean line.

Arithmetic Average Roughness Height is usually measured in micro-inches and denoted by symbol “Ra”.

There are various standards for the roughness of surfaces, set according to their type of application. The equipment used to measure the surface roughness is the so-called “profilometer” (which are available in the contact and non-contact types).

In contact type profilometer the roughness is measured by moving the material under the profilometer stylus. However, modern equipment features non-contact measurements, leveraging the optical and ultrasonic technologies.

Flange AARH

ASME/ANSI defined specific roughness standards for the flanges, as the flange face finish plays a pivotal role in gasket’s reliability and service life.
According to the ASME/ANSI specifications, the serrated, spiral serrated, and concentric flange face finish should have an average roughness of 125 µinch to 250 µinch (3.2 µm to 6.3 µm).

The tool used to imprint a rough finish on the flange should have a radius of 0.06 inch (1.5mm) or larger. The groove density on the flange face should be from 45 grooves per inch to 55 grooves per inch (1.8 grooves/ mm. to 2.2 grooves/ mm.).

These are the standards for semi-metallic and nonmetallic gaskets. If the average roughness of flange face is not according to the described standards, the contacting surfaces would not properly seal and the flanged joint may wear after some time working under pressure (resulting in loss of bolt joint tightness and a possible leakage).

The soft nonmetallic materials such as PTFE may be used for more comfortable facing and better creep resistance.

Allowed AARH imperfections

The sealing performance of the flanges’ gaskets depends on the AARH, the flange dimensions and the pressure of the stud bolts. According to ASME, the adjacent imperfections should be separated by a distance of at least 4 times the maximum radial projection.

The radial projection can be evaluated by subtracting the inner radius from the outer radius.

The serrations shall be at the same level, and the protrusion above them is not permitted. It can cause the adjacent serrations to lose hold of the gasket material and may result in wears and leakages.

Pipe fittings

BUTTWELD FITTINGS

20200304001859 75682 - Pipe, flange, pipe fitting, gasket

Buttweld fittings are available in multiple shapes (elbows, tees, reducers, crosses, caps, stub ends), material grades(carbon, high-yield carbon, low-alloy, stainless, duplex, and nickel alloys), and dimensions (2 to 24 inches in seamless execution, and welded for larger pipe sizes).

The key specifications for buttweld fittings are the ASME B16.9 (carbon and alloy fittings) and the MSS SP 43 (that integrates ASME B16.9 for stainless steel, duplex, and nickel alloy BW fittings).

Butt welding fittings have the following benefits

  • Allow strong, and leak-proof, piping connections
  • Minimize pressure drops and the turbulence inside the pipeline
  • Have a long service life
  • Are rather cheap to purchase and deploy

shapes of butt weld fittings - Pipe, flange, pipe fitting, gasket

For piping systems below 2 inches in diameter, socket weld and threaded (forged) fittings are generally used (ASME B16.11).

BUTTWELD ELBOW 45/90/180 DEG.

ASME B16.9 buttweld elbows are manufactured in a wide range of dimensions (combinations of outside diameter and wall thickness) to fit ASME B36.10 and ASME B36.19 carbon, alloy and stainless steel pipes of any size between 2 and 48 inches (and above).

Buttweld elbows below 24 inches in diameter are produced by cutting, heating and bending seamless steel pipes; pipe elbows of larger sizes are manufactured, instead, from welded pipes or steel plates. 

The three most common types of elbows in piping are the 45, 90, and 180 degrees (or return elbow), as shown in the image:

elbows - Pipe, flange, pipe fitting, gasket
Some special types of pipe elbows are:

  • reducing elbow: a pipe connector with an inlet and an outlet in two different bore sizes is used instead of the combination of a standard elbow and concentric reducer.
  • mitered elbow: large size elbow assembled by joining steel plates

reducing elbow - Pipe, flange, pipe fitting, gasket

SHORT VS LONG RADIUS ELBOW

The center to face distance of a long radius pipe elbow is always 1.5 times the nominal pipe size, whereas, for a short radius pipe elbow, the center to face distance is equal to the nominal pipe size.

Example:

  • For a 4 inches long radius (LR) butt weld elbow, the center to face distance is 4 x 25.4 x 1.5 = 152.4 mm;
  • For a short radius butt weld elbow, the center to face distance is instead 4 x 25.4 x 1 = 101.6 mm. Short radius pipe elbows are available only for the 90 and 180-degree configuration (and not for the 45 degrees); instead, long radius elbows are available for all degrees.

long radius elbows - Pipe, flange, pipe fitting, gasket .       SR elbows - Pipe, flange, pipe fitting, gasket

Manufacturing process of pipe elbow

Buttweld elbows 45 and 90 degrees can be manufactured in different ways, the main ones are the “mandrel process” and the “cold forming” (other methods are the elliptical forming and the double-seam welding method).

Mandrel Process

elbow manufacturing - Pipe, flange, pipe fitting, gasket

Cold forming

elbow cold forming - Pipe, flange, pipe fitting, gasket

Source: TK Bend

PIPE BENDS

A pipe bend is a generic term to indicate a fittings that changes the direction of the piping system (technically, elbows are pipe bends too but of a standardized type in terms of angle degree and direction). The term “pipe bend” refers to a fitting that offsets the direction of the pipe works, without specifying the actual degree and direction.

Pipe bends are manufacturing by twisting a pipe or a tube using a bending machine, with an hot or a cold forming process. Pipe bends are economical ways of making pipe works layouts decreasing the number of other pipe fittings used.

pipe bends 300x243 - Pipe, flange, pipe fitting, gasket

BUTTWELD TEE

EQUAL TEE

An equal tee, otherwise called straight tee, is a buttweld fitting used to branch a pipeline, or any other pipework, at 90 degrees.

 

Equal tee asme b36.19 - Pipe, flange, pipe fitting, gasket

A pipe tee is defined “equal” when the bore size at the run and branch sides have the same diameter. An equal tee is, therefore, used to connect two pipes of the same nominal diameter.

Equal tees are available in sizes from half an inch to 48 inches (or larger) and in seamless and welded execution (seamless up to 24 inches, welded for tee sizes above 24 inches).

Buttweld tees are manufactured according to ASME B16.9 (carbon and alloy) and MSS SP 43 (stainless steel and nickel alloy).

REDUCING TEE

A reducing tee features a smaller bore size at the branched pipe side (generally 2/3 sizes smaller).

In case a larger bore size reduction is necessary, then a reinforced branch connection (such as a Weldolet) shall be preferred to prevent turbulence and have a smoother flow reduction.

reducing tee asme b36.19 - Pipe, flange, pipe fitting, gasket

The standard dimensions and tolerances of equal and reducing pipe tees are covered by the ASME B16.19 specification (carbon and alloy steel) and by the MSS SP 43 spec (for stainless steel and nickel alloys tees).

BARRED TEE

A barred tee is a special type of (equal) tee used for pigging operations (reducing barred tees do not exist, as the pig would not pass through the reduced area anyway).

A barred tee features a welded restriction on the branch pipe side that prevents the pig from flowing from the run pipe into the branched pipe.
Such barred restriction is welded on the internal side of the fitting and looks like a steel cage.

barred tee - Pipe, flange, pipe fitting, gasket

Manufacturing process of pipe tee

Cold forming is the most used manufacturing process for seamless buttweld tees, as illustrated below. Other methods are the single or double seam welding process.

bw tee manufacturing process cold forming - Pipe, flange, pipe fitting, gasket

Source: TK Bend

BUTTWELD CROSS

A Butt weld cross fitting is used when a double branch at 90 degrees is required, which is a rather rare need.

ASME B16.9 and MSS SP43 define the pipe cross dimensions and tolerance. There are no specific limitations in terms of available sizes and schedules for butt weld crosses.

cross fitting asme b36.19 - Pipe, flange, pipe fitting, gasket

 

BUTTWELD REDUCERS

CONCENTRIC REDUCER

The open ends of a concentric reducer are aligned and centered one to the other. Generally, this type of pipe reducer is used to modify the bore size of the pipeline by two (maximum three) measures, to avoid an excessive pressure drop in the pipeline.

If a larger reduction is needed, then a sequence of reducers shall be used to have a smooth and gradual adjustment of the pipeline bore size (vs. a drastic change).

For small bore size reductions, reducing flanges may be an alternative to buttweld reducers.

concentric reducer - Pipe, flange, pipe fitting, gasket

ECCENTRIC REDUCER

The open ends of an eccentric reducer are in an “offset” position one to the other.

Eccentric reducers are used, generally, for pipelines installed in a horizontal position (whereas concentric reducers are used for pipelines installed vertically or for the inlets of suction pumps, as top flat eccentric reducers).

eccentric reducer - Pipe, flange, pipe fitting, gasket

Top and bottom flat eccentric reducer

Eccentric reducers can be top flat (“TF”) or bottom flat (“BF”).
The bottom flat eccentric reducer type is used for pipe-racks (the bottom of the reducer is flat and at the same level of the bigger sized run pipe), while the top flat pipe reducer type is used at the inlet of piping suction pumps as shown in the image below (this setup prevents the formation of vapor traps in the pipeline):
top flat and bottom flat reducers - Pipe, flange, pipe fitting, gasket

Concentric vs eccentric reducer

The key difference between concentric vs eccentric reducer is the centricity of the inlet vs. the outlet of the fitting, which is perfect for a concentric reducer and offset of an eccentric reducer.

Manufacturing process of bw reducer

Cold forming is the most common manufacturing process for seamless eccentric/concentric reducers (welded reducers are produced with the single or double seam weld process):

buttweld reducer manufacturing process - Pipe, flange, pipe fitting, gasket

Source: TK Bend

PIPE CAP

A buttweld pipe cap is used to blind or isolate the pipeline, permanently or temporarily (for example during the execution of maintenance and reparation works).

Buttweld pipe caps are manufactured using steel plates for most sizes and materials. The shape of a pipe cap is ellipsoidal and conforms to the requirements set by the «ASME Boiler and Pressure Vessel» code.

pipe cap asme b36.19 - Pipe, flange, pipe fitting, gasket

Manufacturing process of pipe cap

The manufacturing process of caps starts from steel plates that are cut and shaped with a cold forming procedure:

buttweld cap manufacturing process - Pipe, flange, pipe fitting, gasket

Source: TK Bend

Seamless vs welded bw fittings

Butt weld fittings are available in seamless and welded execution (seamless for bore sizes below 24 inches, welded for sizes above 24 inches).

Seamless buttweld fittings have no seam welds and are therefore considered superior to welded BW fittings (a weld is always a weak point on the metal, prone to corrosion).

Seamless BW fittings are manufactured by cutting, heating and shaping seamless pipes into desired forms. Welded buttweld fittings have one, two or more welds, depending on the dimension, the type of fitting and the manufacturing process adopted by the mill.

Forged Fittings

Socket weld and threaded fittings are available in multiple shapes (elbows, tees, caps, adapters, couplings, etc), sizes (bore sizes between 1/8 and 4 inches, and ratings as 2000#, 3000#, 6000#, 9000#) and material grades (the most common are ASTM A105, ASTM A350 LF1/2/3/6 for low-temperatures, ASTM 182 for corrosive, high-temperature applications). The class of the fitting represents the maximum allowed pressure that the device can withstand.

Class 3000 fittings are used for pipes in schedule 80/XS; Class 6000 for pipes Sch. 160; Class 9000 fittings for pipes with larger wall thickness (XXS).

Forged Elbow 45/90 Degrees

Forged elbows are used to change the direction of the piping system by 45 or 90 degrees. Forged elbows are manufactured according to ASME B16.11 in various material grades, either with socket weld or threaded pipe connections. A special type is the so-called “street elbow”.

street elbow e1528289224652 - Pipe, flange, pipe fitting, gasket
Forged elbows 45 and 90 degrees, street elbow.

Forged Tee (Equal/Reducing)

Forged tees are used to branch a pipe at 90 degrees. Tees can be straight (equal) or reducing.

Forged tees ASME B16.11 are available with socket weld or threaded connections (NPT or BSP). The dimensions of forged tees are covered by the MSS SP 75 and the ASME B16.11 specifications.

 

forged tee - Pipe, flange, pipe fitting, gasket

Forged Lateral

Forged laterals feature a Y shape and are used to branch a pipe at 30-degrees (or different angles, according to the piping specifications).

forged lateral - Pipe, flange, pipe fitting, gasket

Forged Plug (Round, Squared, Hex)

Forged plugs are available with a round, squared or hexagonal head and are used to blind pipes.
forged plug - Pipe, flange, pipe fitting, gasket

Bushings

Hexagonal bushings are manufactured in accordance with ASME B16.11 and are used to join two threaded items of a different size.

hexagonal plug - Pipe, flange, pipe fitting, gasket

Couplings (Half, Full)

Couplings are forged fittings manufactured in accordance with ASME B16.11 and are used to join pipes.

They are available in half or full size and with socket weld or threaded connections (or a combination of the two for special piping applications).

half and full coupling - Pipe, flange, pipe fitting, gasket

Reducers and Reducer Inserts

Reducers are available in two main types, called 1 and 2. They are used to connect pipes and reduce the bore size.

reducers - Pipe, flange, pipe fitting, gasket

Union

Unions are available in the male to female, female to female types, lug nut, and rockwood design. Unions comply with the MSS SP 83 standard.

forged union - Pipe, flange, pipe fitting, gasket

Welding Boss

welding boss e1528288666730 150x150 - Pipe, flange, pipe fitting, gasket

SOCKET WELD FITTINGS

Socket weld fittings are connected to pipes by fillet welds, whereas threaded fittings are screwed onto the pipe (or vice-versa).
A socket weld fitting (left side) and a threaded fitting (right side).

types of forged fittings4 - Pipe, flange, pipe fitting, gasket

Socket weld fittings are used for applications where strong and long-lasting connections are required.  Socket weld fittings are very reliable but are time-consuming to install in a piping system (due to the heavy workload caused by welding operations on small parts).

Socket weld fittings are available in sizes from 1/8 to 4 inches and in classes between 2000# and 9000#.

The typical applications for socket weld fittings are:

  • Steam
  • Explosive fluids and gases
  • Acids and toxic fluids
  • Long service / durable installations

1505911891 2969 cketweld buttweldconnections 300x160 - Pipe, flange, pipe fitting, gasket

Fillet weld vs. Butt Weld: a butt welding connection fills the gaps between two devices, that are beveled at 30 degrees.

THREADED FITTINGS

Threaded fittings are used for less-critical piping systems, such as water distribution, fire protection, and cooling, or for low-pressure installations not subject to vibration, elongation and bending forces. Threaded pipe fittings are not suited for fluids with constantly changing temperatures, as sudden changes may crack the connection.

The two major types of threads are the BSP and NPT, which are not compatible one with the other:

BSP Fittings

BSP means “British Standard Pipe” and can be further divided into the BSPT (tapered) and BSPP (parallel) variations. The threads have a 55° angle in this case. BSP threaded fittings are less common than NPT threaded fittings in the oil and gas industry.

NPT Fittings

NPT stands for “National Pipe Tapered” and is the dominant standard for threaded forged fittings in the oil and gas industry. NPT threading is covered by the ASME B1.20.1 specification and is based on 60° thread flank angles (vs. 55° of the BSP type).

bsp npt - Pipe, flange, pipe fitting, gasket

BSP (BSPP/BSPT) vs NPT: thread angle 55 vs 60 Deg.

BRANCH FITTINGS

Pipe branch fittings are used to create integrally reinforced connections from a run pipe (header pipe) to an outlet pipe, at 45 or 90 degrees, alternatively to connections made with buttweld tees, reinforcing pads and saddles. This type of forged fittings are otherwise called “branch connections”, or “branch fittings”, or “pipe branch outlet fittings” or, simply, “Olets”.

Outlet fittings are forged products with high strength and clear cost advantages over conventional pipe branching techniques.

How are they installed? Quite easily: on one side, the fittings (example a Weldolet) is fixed onto the run pipe with a full penetration groove weld and, on the other side, welded (or screwed) on the branch pipe. Of course, the header pipe shall be properly cut in the proximity of the area where the pipe needs to be branched.

branch fittings - Pipe, flange, pipe fitting, gasket

 

The use of branch fittings instead of conventional fittings (buttweld tee, reinforcing pads and saddles) has the following advantages (example Weldolet):

  • Just 2 welds are needed, instead of 3 (less work and weld inspections)
  • Accelerated installation time
  • Less space is required, making the piping system design more flexible
  • The flow is fully unrestricted, due to the funnel design

Reinforced branch connections are manufactured in a wide range of sizes (to accommodate most size on size or reducing connections), types/designs, connection types (buttweld, socket weld, threaded), and in a wide range of forged steel materials:

  • carbon steel (ASTM A105 for high-temperature, A350 LF2/LF3 for low-temperature)
  • alloy steel (ASTM A182 Grades F5, F9, F11, F22)
  • stainless steel (ASTM A182 F304, F316, and other SS grades)
  • nickel alloys (Inconel, Monel, Incoloy, etc).

The MSS-SP 97 specification covers the dimensions, the finishing, the tolerances, the testing methods and procedures, the marking, the material grades, and the minimum tensile strength requirements for 90-degrees integrally reinforced forged branch outlet fittings (welded and threaded). The connection resulting from using branch fittings complies to ASME B31.1 and ASME B31.3 power and process piping codes.

The types of ends of an outlet fitting shall comply to ASME B16.25 (buttweld ends), or ASME B16.11 (socket weld and threaded ends).

BRANCH FITTINGS

WELDOLET

Weldolets are the most popular type of branch fittings, belong to the buttweld fittings family, and are available in a wide range of dimensions.

A Weldolet has beveled ends at both ends and is, therefore, welded onto the run pipe on one side and onto the branch pipe on the other side. Weldolets are used to create a 90-degrees (reinforced) pipe branch. The shape of the Weldolet ensures little stress concentration on the branched pipe, providing an integral reinforcement.

On the branch pipe side, Weldolets may have the same schedule of the run pipe or a higher schedule.

installed weldolet - Pipe, flange, pipe fitting, gasket

How to install a Weldolet: Bonney Forge

SOCKOLET

Sockolet - Pipe, flange, pipe fitting, gasket

A Sockolet is similar to a Weldolet, with the difference that the branch pipe is connected to the run pipe, via the fitting, with a socket weld connection as per ASME B16.11. Likewise Weldolets, Sockolets are used to make a 90-degree pipe branch. Sockolets may be “size on size” or “reducing”.

Fillet welds are used to connect the branch pipe to the branch side of the Sockolet. On the pipe run side, a Sockolet requires a welded connection.

What is the difference between a Sockolet and a Weldolet?

sockolet vs weldolet e1548078425224 - Pipe, flange, pipe fitting, gasket

Sockolets belong to the “socket fittings” family and are available in classes 3000#, 6000# and 9000#, whereas Weldolets are buttweld fittings. Sockolets are used for lower pressure applications, and smaller pipe diameters, than Weldolets.

THREDOLET

Threadolet MSS Sp97 - Pipe, flange, pipe fitting, gasket

Thredolets are used for low-pressure 90-degree pipe branches. The branch pipe is screwed on the Thredolet, which is welded on the run pipe. The threading is generally of the NPT type and conforms to the ASME B1.20.1 specification.

Thredolets belong to the “threaded fittings” family and are available in classes 3000# and 6000#. Threadolets are used for smaller pipe sizes and low-pressure applications.

LATROLET

Latrolet branch connection - Pipe, flange, pipe fitting, gasket

Latrolets branch a pipe at 45 degrees. They are available with butt weld connections to meet demanding reinforcement requirements or with socket weld/threaded connections in classes 3000# or 6000#.

ELBOLET

Elbolet fitting - Pipe, flange, pipe fitting, gasket

Elbolets are used with 90 or 180 degrees long radius and short radius (more rarely) elbows for thermowell and instrumentation connections or as a drain connection when there is too little space for using a Weldolet.

Elbolets are available with butt weld connections or with socket weld/threaded connections in classes 3000# or 6000#.

NIPOLET

Nipolet - Pipe, flange, pipe fitting, gasket

Nipolets are used for valve take off, drains and vents and are manufactured in lengths between 3 1/2 to 6 1/2 inches and for XS and XXS schedules. A Nipolet is welded onto the run pipe and is manufactured with socket weld or threaded outlets on the branch pipe side.

SWEEPOLET

Sweepolet - Pipe, flange, pipe fitting, gasket
Sweepolets are contoured, integrally reinforced, buttweld branch fittings used for low stress and long fatigue service. The welded connection on the run pipe side can be easily inspected with radiographic examination (RX or RT), ultrasounds (UT) and other non-destructive tests.

How to order branch fittings

Suppliers of Weldolets, Thredolets, Sockolets, and other branch fittings need the following information to identify the needed product:

  • Header run pipe size (which is generally expressed as a range of possible sizes, example 36-22)
  • Branch pipe size (the NPS of the connecting pipe to the run pipe, example 6 inches)
  • Branch pipe schedule (which can be STD, XS, 160, XXS) for buttweld types of connections (rating shall be provided for socket weld and NPT threaded Olets)
  • Style of branch fitting (Weldolet, Thredolet, Nipolet, Sockolet, etc)
  • Material Grade (example A105, A350 LF2, A182 F304)

Flange gasket

Leakage is the main failure mode of pipe flange, which is related to many factors such as sealing structure type, rigidity of connected parts, performance of sealing parts, operation and installation.
Gasket is the main seal of flange connection, so the correct selection of gasket is also the key to ensure that the flange connection does not leak.
There are many kinds of flange gasket selected according to the corrosiveness, temperature, pressure and the form of flange sealing surface of the medium transported by the pipeline. Pipe flange gasket has non-metallic gasket, semi-metallic gasket and metal gasket.
Rubber asbestos pad
Rubber asbestos gasket is the most widely used gasket for flange connection, which can be applied to many media, such as steam, gas, air, salt water, acid and alkali, etc. The thickness of rubber asbestos pad is not uniform in all disciplines, usually 3mm thick. For flange with nominal diameter less than 100mm, the gasket thickness shall not exceed 2.5mm.
Gasket pressure: not more than 2.5MPa when used for smooth sealing surface flange connection.
There are two types of rubber asbestos pads commonly used in the refining industry:
One is oil-resistant rubber asbestos pad, which is suitable for transportation of general oil, liquefied hydrocarbon, propane, acetone and other media with temperature below 200 ℃ and nominal pressure below 2.5MPa. The high temperature oil resistant rubber asbestos pad can be used at 350-380 ℃.
The other is medium pressure rubber asbestos pad, which can be used in steam, condensate, water, air and other media under 200 ℃, PN2.5MPa. Since asbestos has been proved to be carcinogenic, asbestos containing gaskets are now largely out of use.
Rubber mat
Rubber gasket is a gasket made of rubber plate, which has certain corrosion resistance. It is commonly used for the flange connection of pipes conveying low-pressure water, acid and alkali with temperature below 60 ℃ and pressure no more than 1.0MPa.
The gasket is characterized by the use of rubber elasticity to achieve better sealing effect, so it is also commonly used in the installation of cast iron flange valves.
Spiral wound gasket
Spiral wound gasket is short for spiral wound gasket, which is wound by metal steel strip and non-metal filler strip.
Advantages: the gasket has the advantages of simple manufacture, low price, full utilization of materials and good sealing performance, and is widely used in petrochemical process pipeline.
Applicable parameters: the applicable nominal pressure is less than 4.0Mpa, and the applicable temperature range is as follows: the temperature of 08 steel can reach 450 ℃, and the winding pad made of 0Cr13 steel strip can reach 540 ℃. The thickness of gasket is generally 4.5mm. When the diameter is greater than 1000mm, the thickness of gasket is 6-7mm. The thickness of the locating ring is about 3mm.
This kind of gasket is mostly used for smooth flange connection, and its sealing surface does not need water line. Some spiral wound gaskets also have locating rings to prevent the gasket from deviating from the flange center.
The material of metal belt includes 08 steel, 0Cr13 steel, 1Cr18Ni9Ti steel, etc.; the material of non-metal belt includes characteristic asbestos, flexible graphite, polytetrafluoroethylene, etc.
Toothed cushion
The toothed pad is made of various metals, including ordinary carbon steel, low alloy steel and stainless acid resistant steel, with a thickness of 3-5mm.
It makes use of the tooth pattern of concentric circle to contact with the flange sealing surface to form a multi-channel seal. Therefore, it has good sealing performance and is commonly used for the connection of the concave convex sealing surface flange.
Applicable parameters: the maximum nominal pressure can be up to 16.0mpa, which is suitable for the parts with high working temperature, such as 0Cr13 tooth shaped gasket, whose applicable temperature can be up to 530 ℃.

Types of spiral wound gasket

A few different types of spiral wound gaskets exist, depending on:

  • the number of rings (outer and inner)
  • the materials of the inner and the outer ring of the gasket

spiral wound gaskets types - Pipe, flange, pipe fitting, gasket

  • Type 00: Spiral Wound Gasket without rings: they are used for tongue and groove, male and female flanges.
  • Type 01: Spiral Wound Gasket with inner ring: they are used for male and female or special flange types.
  • Type 10: Spiral Wound Gasket with outer ring: they are used for raised face flanges.
  • Type 101: Spiral Wound Gasket with inner and outer rings: they are used for raised face flanges.
  • Special Section: Spiral Wound Gasket with special rings: they are used for special flanges and special usage.

Each manufacturer, of course, has specific codes to designate the different spiral wound gasket types, but the typical designs are recurring regardless of the producer.

The image shows how the different spiral wound gasket types used for flanged joints in piping applications:

profiles of spiral wound gaskets - Pipe, flange, pipe fitting, gasket

Metal washer
There are many kinds of metal washers. According to their shapes, they are divided into metal flat washers, oval, octagonal metal washers and lens washers. According to the manufacturing materials, there are low carbon steel, stainless acid resistant steel, copper, aluminum and lead.
Metal flat washer, mostly used for smooth surface flat welding flange, with low temperature and pressure.
Elliptical and octagonal metal washers are mostly used for butt welding flange with trapezoid groove, and the nominal pressure range is 6.4-22.0mpa. Although this kind of gasket has good sealing performance, its manufacture is complex and requires high precision.
There is a principle in the use of metal gasket, that is, the hardness of gasket surface must be lower than that of flange sealing surface.
The selection of gasket shall be determined according to the temperature, pressure, corrosiveness of the medium transported by the pipeline and the sealing form of the connecting flange. Professional gasket, such as lens gasket, is suitable for high pressure flange connection.

Bolts for flange

There are two kinds of bolts for connecting flange, single head bolt and stud bolt. The thread is generally triangular metric coarse thread.
Single head bolt
Single head bolt is also called hexagon head bolt. Single head bolts are divided into two types: semi refined and refined. In the medium and low pressure process pipeline, the most commonly used is semi refined single head bolts.
The commonly used materials for manufacturing single head bolts are Q235A, 35 steel, 25Cr2MoVA, etc. It is commonly used for flange connection with nominal pressure less than 2.5MPa.
The applicable temperature depends on the bolt material. For example, the applicable temperature of bolts made of 35 steel can reach 350 ℃; the applicable temperature of bolts made of 25Cr2MoVA steel can reach 570 ℃
Studs
Most of the studs used in the process pipeline are made of equal length studs. Suitable for flange connection with high temperature and pressure.
It is made of 35 steel, 30crmoa, 35CrMoA, 25Cr2MoVA, 0Cr19Ni9, 0cr15ni25ti2moalvb and 37simn2mova, with nominal pressure range of 1.6-32.0mpa and applicable temperature of 700 ℃.

 Nuts

Nuts, collectively referred to as hex nuts. It is divided into semi refining and refining. According to the structure of the nut, it can be divided into a type and B type.
Semi refined single head bolts are mostly A-type nuts, while refined stud bolts are mostly B-type nuts. Nuts and bolts shall be used together, but the hardness of nut manufacturing material shall not exceed that of bolt material.

Semi refined single head bolts are mostly A-type nuts, while refined stud bolts are mostly B-type nuts. Nuts and bolts shall be used together, but the hardness of nut manufacturing material shall not exceed that of bolt material.

Source: China Pipe Fittings Manufacturer – Yaang Pipe Industry (www.epowermetals.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@epowermetals.com Please notice that you might be interested in the other technical articles we’ve published:

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pipe flange pipe fitting gasket - Pipe, flange, pipe fitting, gasket
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Pipe, flange, pipe fitting, gasket
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www.epowermetals.com has 3 warehouses in Wenzhou, Wuxi and Hebei. As one of the piping solution suppliers, Epower Metals has been committed to providing one-stop solutions for projects in the fields of oil and gas, water, renewable energy and infrastructure​.
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