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

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

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:
❶ 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

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

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

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 C° W/m K	Spec. thermal capacity at 20 C° J/kg K	Spec. electrical resistivity at 20 °C Ω mm²/m
	20 C°	300 C°	400 C°	450 C°
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 finishing and testing

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

 

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

SLIP ON FLANGE

     

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 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

 .        

LAP JOINT FLANGE

Special types of flanges

NIPOFLANGE

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

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.

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

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

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).

The drawing of an ASME expanding flange.

Reducing flange (“reducer”)

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

Pipe fittings

BUTTWELD FITTINGS

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

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:

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

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.

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Manufacturing process of pipe elbow

 

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”.

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 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 Plug (Round, Squared, Hex)

Forged plugs are available with a round, squared or hexagonal head and are used to blind pipes.

Bushings

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

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).

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.

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.

Welding Boss

SOCKET WELD FITTINGS

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

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 (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.

 

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

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.
❶ 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.
❸ 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

• 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:

❺ 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.
❶ 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 ℃
❷ 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 ℃.

❸ 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 [email protected] Please notice that you might be interested in the other technical articles we’ve published:

• What is a flange
• What is a steel pipe
• What is pipe fitting