Manufacturing technology points and quality control of UNS N10276 seamless heat exchanger tube

Introduces Ф19.05 * 2.65mm UNS N10276 seamless heat exchanger tube manufacturing key manufacturing process and fine quality control, thereby improving its product quality to meet or exceed foreign quality brands, reduce imports, shorten the delivery cycle, reduce the cost of equipment to meet the equipment with high-quality products for a long period of operation.

In the power plant desulfurization and denitrification, fine chemicals, PTA, and other corrosive environment device project, the widespread use of Hastelloy UNS N10276 condenser equipment and Hastelloy C-276 seamless heat exchanger tube is an extremely important part of the equipment. A fine chemical plant 1 Hastelloy C-276 alloy condenser heat exchanger equipment, designed and manufactured in 2007, put into use in 2008, running to 2014 heat exchanger tube leakage. The reason is due to the corrosive gas medium flow rate is very fast, fluid impact and scrub shell process inlet heat exchanger tube, so that the vibration of the bending deformation; the original seamed heat exchanger tube weld corrosion, wall thinning perforated leakage, did not reach the original design of the condenser equipment service life. Solution: Redesign and manufacture the equipment and replace it during overhaul. Improve the original seamless heat exchanger tube for the seamless heat exchanger tube while improving the structure and arrangement of the components, such as the impact plate, increase the media circulation area, and slow down the flow rate. Hastelloy C-276 heat exchanger tube from the manufacturing quality considerations, in the past, mainly purchased from imports of heat exchanger tube, the quality is good. Still, the delivery period is long and expensive. In the production device overhaul and transformation period, the construction period is short, and with less investment, heat exchanger localization of refined manufacturing becomes very necessary.

1. Parameters of UNS N10276 seamless heat exchanger tube

Standard ASME SB-622, UNS N10276 seamless heat exchanger tube specifications: Ф19.05 * 2.65mm, length L = 5407mm, quantity 1662.

2. Manufacturing process of UNS N10276 seamless heat exchanger tube

2.1 Carefully organize the preparation of manufacturing technology programs

The technical department of the steel pipe manufacturing plant should be carefully organized with rich experience in the preparation of engineers through the technical expert’s group meeting review and approval of the company’s chief engineer. Preparation of the basis for compliance with ASME SB622 “seamless nickel and nickel-cobalt alloy nominal pipe and tube,” ASME SB829 “nickel and nickel alloy seamless nominal pipe and tube General Requirements,” the steel pipe manufacturing plant’s “Hot Extrusion Process Operating Procedures,” “Cold Processing Process Operating Procedures” and so on as the basis of the technical program including hot extrusion, cold rolling, heat treatment, pickling, and other process technologies. Technical program to be issued to the production team and the team manufacturing workers for technical briefing.
Heat exchanger pipe purchasers, but also to organize the purchaser’s technical expert group meeting review, the main content is to monitor which important processes, which tolerances need to focus on quality control, and the preparation of quality supervision and control procedures to guide the quality inspection engineers to inspect and witness inspections.

2.2 Manufacturing process flow of UNS N10276 seamless heat exchanger tube

The manufacturing process guides the production of the outline in the production preparation stage posted in the production workshop workstation on the board. The seamless heat exchanger manufacturing process flow is shown in Figure 1.

Figure.1 Seamless heat exchanger manufacturing process flow

2.3 Round bar billets into the factory acceptance

The incoming quality of raw materials is the source of subsequent processing and manufacturing quality. Round steel billet using electric furnace smelting heating furnace refining process to produce products, surface processing into a smooth state. The ingot head and tail must be fully removed, and the weight percentage must be recorded in the material certificate. Iron and steel mills must provide the original quality certificate of billet; recorded data must be clear, complete, and correct, while the billet physical markings should also be clear and accurate, consistent with the original warranty.
Raw material round steel billet also by the provisions of ASTM A751 method of chemical composition analysis test, each furnace arbitrarily takes a sample of round steel, the results must meet the requirements of the standard ASTM B880 elemental content; low times the organization of the test, the test method by the provisions of GB 226: size and surface quality inspection by root.

2.4 Hot extrusion

The purpose is to the large size of the round steel billet through the hot extrusion process to reach the small size of the cold rolled pipe hot extrusion process technology by the steel pipe manufacturing plant “Extrusion Process Operating Procedures.” Purchasers must send inspectors to supervise and witness the internal surface with endoscopic inspection. Extruded billet surface shall not have cracks, folding, scars, inclusions, lugs, or other defects, such as these defects must be repaired and ground cleanly, the diameter of the repaired grinding place does not exceed the permissible negative deviation, and smooth transition.

2.5 Cold rolling technology

Determine the cold rolled process route, determining the size of the cold rolling process, and the number of cold rolled is the key to the manufacture of heat exchanger tube. The process route is as follows: the first specification pipe cold rolled to the second specification pipe, and then cold rolled to the third specification pipe, and then cold rolled to the fourth specification pipe, and then cold rolled to the fifth specification pipe, and then cold rolled to the final specification Φ19.05 * 2.65mm.
Cold rolling, cold rolling mill selected holes, top head, and other molds shall not have any abrasion, surface hardness HRC ≥ 58-60 °. Before starting the cold rolling mill, the mill’s hydraulic system, process lubrication system, equipment lubrication system, transmission system, electronic control system, and other related parts of the inspection the normal before driving. Pipe rolling, the inner surface should be coated with lubricant.
The first tube rolled out; we must check the surface quality and size deviation; when the rolled-out tube does not meet the process requirements, we must adjust the outer diameter or wall thickness of the rolled steel pipe by adjusting the mandrel seat of the front and back movement and adjust the hole type oblique wedge screw to achieve the up and down movement of the roll to adjust the outer diameter and size of the rolled-out steel pipe. Roll out the appearance of steel pipe rolling injuries, rolling hair phenomenon or poor quality of the appearance, to stop to check the quality of incoming materials or grinding holes, grinding holes, not allowed to focus on one grinding, circumference and longitudinal must be polished at the same time, so that the smooth transition of the sanding place, do not allow the existence of craters. Rolling in the hard to see, hard to measure, hard to check rolled steel pipe size tolerance and the quality of the external surface and the surface of the head.

2.6 Pickling, degreasing

Operation process: pickling, degreasing → cleaning → rinsing → hot water washing. Pickling with HF + HNO₃ + H2O mixture, the ratio is as follows: HF: 3% -5%; HNO₃: 10% -15%; the rest: H₂O; temperature: 40-60 ℃. Degreasing using HNO₃ + H₂O mixture, the ratio is as follows: HNO₃: 8% -15%; the rest: H₂O; temperature: 30-40 ℃. Pickling, degreasing operation, gently hold and put, to prevent abrasions and bruises, steel pipe under the cylinder before the solution is stirred, and then the head low tail high tilt into the cylinder, lifting must be head high tail low lifting out of the pipe so that the water and residual acid outflow, and with water promptly to flush away the surface of the residual floating oil and so on. Degreasing and pickling of the steel pipe must do five no: no over-acid, no under-acid, no oil, no lime, and no acid residue.

2.7 Heat treatment process of UNS N10276 seamless heat exchanger tube

Heat treatment in the roller bottom-type natural gas continuous furnace, pipe traveling at a constant speed, the atmosphere of the furnace chamber is a weak oxidizing atmosphere, the intermediate solution heat treatment temperature (1140 ± 15) ℃, the finished product heat treatment temperature (1120 ± 10) ℃, the speed according to the specific product wall thickness to determine.

3. Quality control of UNS N10276 seamless heat exchanger tube

3.1 Preparation of quality inspection program (ITP), divided into key inspection processes, set up to stop the inspection point.

Pipe production plant quality department to organize the preparation of a “quality inspection plan” (ITP), technical quality experts review, approval of the chief engineer, and the buyer’s quality department review. The program specifies the content of each manufacturing process inspection, the implementation of standards and methods, inspection records or report forms, set the type of checkpoints. Divide the key processes in Table 2.
3.2 Purchasers to send professional quality control engineers for all process quality inspection and monitoring, supervision, and witness the quality of each process in the production process, the quality of the original records separate and carefully recorded.
Table.2 Production process and inspection set point type

Item	Production process	Set point type
1	Prerequisite check	Stop Hold Point
2	Raw material acceptance	Witness point
3	Blank preparation	Witness point
4	Hot extrusion (to the first specification mm)	Witness point
5	Inspection of extruded tube blanks	Stop Hold Point
6	Cold rolled (2nd specification mm)	Stop Hold Point
7	Intermediate heat treatment	Stop Hold Point
8	Cold rolled (3rd specification mm)	Witness point
9	Intermediate heat treatment	Witness point
10	Cold rolled (4th specification mm)	Witness point
11	Intermediate heat treatment	Witness point
12	Cold rolling (5th specification mm)	Witness point
13	Intermediate heat treatment	Witness point
14	Cold rolling (sixth specification mm)	Witness point
15	Intermediate heat treatment	Witness point
16	Finished cold rolling (19.05×2.65mm)	Stop Hold Point
17	Finished product heat treatment	Stop Hold Point
18	Ultrasonic inspection	Stop Hold Point
19	Hydrostatic test	Stop Hold Point
20	Eddy current inspection	Stop Hold Point
21	Chemical composition analysis of finished products	Written Witness Point
22	Room temperature Tensile testing	Written Witness Point
23	Flaring test	Written Witness Point
24	Intergranular corrosion test	Written Witness Point
25	Size/surface/identification/packaging inspection	Witness point

4. Inspection methods of UNS N10276 seamless heat exchanger tubes

• (1) Chemical composition analysis. Any 1 per furnace, according to the provisions of ASTM A751, chemical analysis of the composition of deviations should meet the requirements of ASTM B880.
• (2) Mechanical properties test. For each batch of any 1 branch according to the provisions of the ASTM A370 test, the results comply with tensile strength (R_m/MPa) ≥ 690; yield strength (R_p0.2/MPa) ≥ 283; elongation (A/%) ≥ 40.
• (3) Flaring test. Each batch of 1 branch of steel pipe is according to the requirements of the ASTM B829 flare test. The top core taper of 60 degrees, and the outer diameter flaring rate of 30%. After the flaring test, the specimen shall not appear to penetrate the wall thickness of the crack.
• (4) Intergranular corrosion test. Each batch of any 2 (different branches of steel pipe) steel pipe by ASTM G28A method of intergranular corrosion test, the test cycle of 24 h. After the test with the bending method of specimen evaluation, the bending surface does not crack on behalf of the specimen is qualified.
• (5) Hydraulic test. Steel pipe root by root hydraulic test, hydraulic test pressure of 7.0MPa. In the test pressure, the stabilization time is at least 5s; the steel pipe should not leakage phenomenon.
• (6) Ultrasonic test. Pipe according to the provisions of ASTM B829 and ASTM E213 root-by-root full-length ultrasonic flaw detection inspection of longitudinal defects. Ultrasonic flaw detection test comparison sample tube groove depth of 0.2mm.
• (7) Eddy’s current inspection. Pipe according to the provisions of ASTM B829 and ASTM E571 root-by-root full-length eddy current flaw inspection. Eddy’s current flaw inspection and comparison of sample pipe drilling diameter of not more than 0.8mm.
• (8) Size inspection. Finished steel pipe test size, allow deviation of the outer diameter of plus or minus 0.19mm, wall thickness of plus or minus 10%.
• (9) Surface quality inspection. Finished pipe pickling passivation treatment, if the surface has defects to be machined or grinding, after processing, the local wall thickness is equal to the minimum required wall thickness. The inner and outer surfaces of the tube are free of cracks, folds, roll marks, delamination and scars, oxidized skin, staining, grease, and paint. Finished product inspection stand after wiping, no stains on the surface; the operator should wear new white gloves to contact the surface of the pipe, prohibit empty-handed contact with the surface of the tube, the tube before the transfer of all needs to be wrapped in plastic, the transfer process is light, light, the entire inspection, packaging process is strictly prohibited secondary pollution and damage.

5. Packaging of UNS N10276 seamless heat exchanger tubes

Pipe packaging, marking, and quality certification align with the purchaser’s provisions and standards. The mark on the surface of the pipe contains the manufacturer, material name, standard, furnace number, and specifications.

6. Conclusion

To produce high-quality heat exchange tubes, it is not only necessary for the operators to refine the operation of each process but also for the procurement party and professional quality inspection engineers of the manufacturing factory to do a good job in fine quality monitoring and inspection.

• 1) Operators control the dimensional deviation of each process to reduce the scrap rate;
• 2) After each cold rolling process, it is necessary to degrease, heat treat, straighten, pickle, and inspect before proceeding with the next cold rolling process. The first and last cold rolling processes are very important, and professional inspectors need to be sent to inspect the inner surface with an endoscope to check if any impurities have entered the surface or if there are defects on the surface that have not been treated;
• 3) The quality of acid pickling and oil removal is directly related to the surface quality of steel pipes, the normal and effective cold working process. Also, it affects the intergranular corrosion resistance of pipes. Therefore, it is important to focus on the quality of the two processes of acid pickling and oil removal;
• 4) Finished products should be subjected to ultrasound, water pressure, and eddy current, and no one should be omitted.

Author: Zhang Chao