ASTM A276 TP304/304L Stainless Steel Welded Pipes: Standards, Properties, Manufacturing, Applications and Quality Control

2.1 Scope of Application

• Pipes used in industrial pipelines for transporting corrosive media (such as acids, alkalis, salts, and organic solvents), high-temperature media (such as steam and hot oil), and food-grade media (such as drinking water, milk, and food additives);
• Pipes used in petrochemical, chemical, pharmaceutical, food processing, water treatment, marine engineering, and other industries;
• Welded pipes with outer diameter ranging from 10.3 mm (0.405 in.) to 1219.2 mm (48 in.) and wall thickness ranging from 0.89 mm (0.035 in.) to 25.4 mm (1.0 in.), which can be divided into seamless welded pipes and longitudinal welded pipes according to the welding method.

 

2.2 Core Technical Requirements of the Standard

2.2.1 Chemical Composition Requirements

2.2.2 Dimensional Accuracy Requirements

2.2.3 Surface and Internal Quality Requirements

2.3 Relationship with Other Relevant Standards

• ASTM A312 Standard: This standard applies to stainless steel seamless and welded pipes for high-temperature and high-pressure pipelines, which is more stringent than ASTM A276 in terms of pressure-bearing capacity and high-temperature performance. TP304/304L pipes meeting ASTM A312 standard can be used in boiler, pressure vessel, and other high-temperature and high-pressure applications.
• ASTM A249 Standard: This standard applies to austenitic stainless steel welded pipes for boiler and heat exchanger, which focuses on the high-temperature oxidation resistance and creep performance of the pipes. It is mainly used in heat exchanger tubes and boiler tubes.
• GB/T 12771 Standard: This is a Chinese national standard for stainless steel welded pipes for fluid transport, which is equivalent to ASTM A276 in scope of application and technical requirements. The 06Cr19Ni10 (TP304) and 022Cr19Ni10 (TP304L) pipes in GB/T 12771 can be used interchangeably with ASTM A276 TP304/304L pipes in general applications.
• ASME SA-276 Standard: This standard is the boiler and pressure vessel standard adopted by the American Society of Mechanical Engineers (ASME), which is equivalent to ASTM A276 but more stringent in quality control. TP304/304L pipes used in boiler and pressure vessel applications must comply with ASME SA-276 standard.

3. Chemical Composition and Mechanical Properties of ASTM A276 TP304/304L Stainless Steel Welded Pipes

3.1 Analysis of Chemical Composition Differences

3.2 Mechanical Properties

3.2.1 Analysis of Mechanical Property Differences

3.2.2 Mechanical Property Test Methods

• Tensile Test and Yield Strength Test: These tests are carried out using a universal testing machine. The test sample is a standard round bar sample cut from the welded pipe, and the gauge length of the sample is 50 mm (2 in.). The test speed is controlled at 2-5 mm/min to ensure the accuracy of the test results. During the test, the tensile force and elongation of the sample are measured, and the tensile strength and yield strength are calculated according to the test data.
• Brinell Hardness Test: This test is carried out using a Brinell hardness tester, with a test load of 3000 kgf and a steel ball diameter of 10 mm. The test point is selected on the cross-section of the pipe, and at least three test points are taken for each sample to calculate the average value, which is taken as the hardness value of the pipe. It should be noted that the test point should avoid the welding seam to prevent the welding seam from affecting the test results.
• Impact Toughness Test: This test is carried out using an Izod impact tester. The test sample is a standard V-notch sample cut from the welded pipe, and the test temperature is 23℃ (room temperature). During the test, the impact energy absorbed by the sample when it is broken is measured, which is the impact toughness value of the pipe.

4. Welding Process of ASTM A276 TP304/304L Stainless Steel Welded Pipes

4.1 Common Welding Methods

4.1.1 Key Welding Method: GTAW (TIG) Welding

• Shielding Gas Selection: Argon (Ar) is usually used as the shielding gas, with a purity of not less than 99.99%. Argon has good shielding effect, which can prevent the welding pool and weld seam from being oxidized by air, and avoid the formation of defects such as pores and oxides. For pipes with larger wall thickness, a small amount of helium (He) can be added to the shielding gas to increase the welding temperature and improve the weld penetration.
• Welding Wire Selection: The welding wire should be consistent with the chemical composition of the base metal. For TP304 pipes, ER308 welding wire is used; for TP304L pipes, ER308L welding wire is used. The diameter of the welding wire is usually 1.0-2.0 mm, which is selected according to the wall thickness of the pipe. The welding wire should be cleaned before use to remove oil, rust, and other impurities on the surface.
• Welding Parameter Control: The key welding parameters include welding current, welding voltage, welding speed, and shielding gas flow. For TP304/304L pipes with wall thickness of 2-6 mm, the welding current is controlled at 50-120 A, the welding voltage is 8-12 V, the welding speed is 5-10 cm/min, and the shielding gas flow is 8-15 L/min. Too high welding current will lead to excessive heat input, large heat-affected zone, and easy formation of cracks; too low welding current will lead to insufficient weld penetration and incomplete fusion.
• Welding Operation: The welder should hold the welding torch at an angle of 70-80° with the base metal, and the distance between the welding torch and the base metal is 3-5 mm. The welding wire should be fed into the welding pool evenly to ensure that the weld seam is full and uniform. During the welding process, the welding torch should move stably to avoid fluctuations in welding speed and current.

4.2 Welding Process Control

4.2.1 Pre-Welding Preparation

• Base Metal Cleaning: Before welding, the surface of the base metal (especially the groove and its surrounding area within 20 mm) must be cleaned to remove oil, rust, oxide scale, and other impurities. Oil can be removed by degreasing agents (such as acetone and ethanol); rust and oxide scale can be removed by grinding, pickling, and other methods. The purpose of cleaning is to prevent impurities from entering the weld pool during welding, which may cause defects such as porosity, inclusions, and incomplete fusion. In practical operation, after cleaning, the surface of the base metal should be inspected visually to ensure that there are no visible impurities, and the cleaned surface should be welded within 4 hours to avoid secondary pollution.
• Groove Processing: The groove form of TP304/304L stainless steel welded pipes is mainly determined by the wall thickness of the pipe. For thin-walled pipes (wall thickness ≤6 mm), a V-shaped groove with an angle of 60-70° is usually adopted, and the root gap is 2-3 mm, which is conducive to full weld penetration and uniform weld formation. For medium-thick wall pipes (6-15 mm), an X-shaped groove or U-shaped groove can be adopted to reduce the amount of welding filler metal, reduce heat input, and avoid excessive deformation of the pipe. The groove processing can be carried out by grinding, cutting, or planing, and the surface of the groove should be smooth, free of burrs, cracks, and other defects. The roughness of the groove surface should not exceed 6.3 μm (Ra) to ensure good contact between the welding wire and the base metal.
• Assembly: During the assembly of the pipes, the coaxiality of the two pipes should be ensured, and the deviation of the pipe axis should not exceed 0.5 mm per meter. The root gap and misalignment should be strictly controlled according to the groove design requirements. The misalignment of the pipe wall should not exceed 10% of the wall thickness, and the maximum misalignment should not exceed 2 mm. If the misalignment is too large, it will lead to uneven stress distribution in the weld seam, increase the risk of cracks, and affect the mechanical properties of the pipe. After assembly, the pipes should be fixed with clamps to prevent displacement during welding.

4.2.2 Welding Parameter Control

4.2.3 Post-Welding Treatment

• Post-Welding Cleaning: After welding, the surface of the weld seam and the heat-affected zone will have welding spatter, slag, and oxide scale, which need to be cleaned in time. Welding spatter can be removed by chiseling, grinding, or sandblasting; slag can be removed by wire brushing or grinding. The cleaning should be thorough to avoid residual slag and spatter affecting the subsequent heat treatment and pickling passivation effect. In addition, the weld seam should be inspected visually after cleaning to check whether there are visible defects such as cracks, pores, and incomplete fusion.
• Post-Welding Heat Treatment: The post-welding heat treatment of TP304/304L stainless steel welded pipes mainly adopts solution heat treatment, which is the key to restoring the corrosion resistance and mechanical properties of the pipe. Solution heat treatment is carried out in a heat treatment furnace, and the specific process parameters are as follows: heating temperature 1050-1100℃, holding time 30-60 minutes (depending on the wall thickness of the pipe), and then rapid cooling (water cooling or air cooling). The purpose of solution heat treatment is to dissolve the chromium carbide (Cr₂₃C₆) precipitated at the grain boundaries during welding, restore the uniform austenitic structure, and form a dense chromium oxide passive film on the surface of the pipe, thereby improving the intergranular corrosion resistance and mechanical properties of the pipe. It should be noted that the heating rate and cooling rate should be strictly controlled during solution heat treatment. The heating rate should not exceed 200℃/h to avoid thermal stress and cracks; the cooling rate should be fast enough to prevent the re-precipitation of chromium carbide.
• Pickling and Passivation: After welding and heat treatment, the surface of the pipe and the weld seam area will still be covered with oxide scale, discoloration, and residual contaminants, which will damage the passive film and reduce the corrosion resistance of the pipe. Therefore, pickling and passivation treatment is required to restore and enhance the corrosion resistance of the pipe.

5. Manufacturing Technology of ASTM A276 TP304/304L Stainless Steel Welded Pipes

5.1 Raw Material Selection

5.2 Plate Cutting

• Shearing: This method is suitable for cutting thin-walled stainless steel plates (thickness ≤6 mm). It has the advantages of high cutting efficiency, low cost, and smooth cutting surface. The shearing equipment mainly includes hydraulic shears and mechanical shears. When shearing, the cutting edge should be sharp, and the clearance between the upper and lower cutting edges should be adjusted according to the thickness of the plate (usually 5%-10% of the plate thickness) to avoid burrs and deformation of the cutting surface.
• Plasma Cutting: This method is suitable for cutting medium-thick wall stainless steel plates (thickness 6-25 mm). It has the advantages of fast cutting speed, high cutting accuracy, and strong adaptability. The plasma cutting uses high-temperature plasma arc to melt the stainless steel plate, and then blows off the molten metal with high-pressure gas to complete the cutting. When plasma cutting, the cutting parameters (such as plasma arc current, voltage, and cutting speed) should be strictly controlled to ensure the cutting quality. The cutting surface should be smooth, free of burrs, and the cutting deviation should not exceed ±0.5 mm.
• Laser Cutting: This method is suitable for cutting high-precision stainless steel plates of various thicknesses. It has the advantages of high cutting accuracy, smooth cutting surface, and small cutting deformation. The laser cutting uses high-energy laser beam to melt and vaporize the stainless steel plate, and the cutting accuracy can reach ±0.1 mm. However, the laser cutting equipment is expensive, and the cutting cost is high, which is mainly used for cutting high-precision, small-batch pipes.

5.3 Forming

5.3.1 Roll Forming

5.3.2 Press Forming

5.4 Welding, Post-Welding Treatment and Finished Product Inspection

• Dimensional Inspection: The dimensional inspection includes the inspection of outer diameter, wall thickness, length, straightness, and roundness. The inspection methods are in accordance with Table 2. The inspection should be carried out randomly, and the sampling ratio should not be less than 5% of the total number of pipes. If unqualified products are found, the sampling ratio should be increased, and all unqualified products should be repaired or scrapped.
• Surface Quality Inspection: The surface quality inspection is mainly carried out by visual inspection and magnifying glass inspection. The inner and outer surfaces of the pipe should be smooth, free of cracks, inclusions, scratches, pits, folds, and other defects. The surface roughness should meet the requirements (hot-finished pipes ≤6.3 μm Ra, cold-finished pipes ≤1.6 μm Ra). For pipes used in food-grade and pharmaceutical applications, the surface should be inspected more strictly to ensure that there are no dead corners and easy cleaning.
• Internal Quality Inspection: The internal quality inspection mainly adopts non-destructive testing methods, including ultrasonic testing (UT), radiographic testing (RT), and magnetic particle testing (MT). For thick-walled pipes (wall thickness >15 mm), ultrasonic testing and radiographic testing must be carried out to check internal defects such as cracks, pores, and incomplete fusion. The testing results should comply with the requirements of ASTM A276 standard. For pipes used in important applications, 100% non-destructive testing should be carried out.
• Chemical Composition Inspection: The chemical composition inspection is to take samples from the finished pipes and test their chemical composition by optical emission spectroscopy (OES) or X-ray fluorescence (XRF). The test results should be within the range specified in Table 1. The sampling ratio should not be less than 3% of the total number of pipes.
• Mechanical Property Inspection: The mechanical property inspection includes tensile test, yield strength test, elongation test, hardness test, and impact toughness test. The test methods and requirements are in accordance with Table 3. The test samples should be taken from the finished pipes, and the sampling ratio should not be less than 2% of the total number of pipes. The test results must meet the minimum requirements of ASTM A276 standard.

4.2.3 Post-Welding Treatment

• Post-Welding Cleaning: After welding, the surface of the weld seam and the heat-affected zone will have welding spatter, slag, and oxide scale, which need to be cleaned in time. Welding spatter can be removed by chiseling, grinding, or sandblasting; slag can be removed by wire brushing or grinding. The cleaning should be thorough to avoid residual slag and spatter affecting the subsequent heat treatment and pickling passivation effect. In addition, the weld seam should be inspected visually after cleaning to check whether there are visible defects such as cracks, pores, and incomplete fusion.
• Post-Welding Heat Treatment: The post-welding heat treatment of TP304/304L stainless steel welded pipes mainly adopts solution heat treatment, which is the key to restoring the corrosion resistance and mechanical properties of the pipe. Solution heat treatment is carried out in a heat treatment furnace, and the specific process parameters are as follows: heating temperature 1050-1100℃, holding time 30-60 minutes (depending on the wall thickness of the pipe), and then rapid cooling (water cooling or air cooling). The purpose of solution heat treatment is to dissolve the chromium carbide (Cr₂₃C₆) precipitated at the grain boundaries during welding, restore the uniform austenitic structure, and form a dense chromium oxide passive film on the surface of the pipe, thereby improving the intergranular corrosion resistance and mechanical properties of the pipe. It should be noted that the heating rate and cooling rate should be strictly controlled during solution heat treatment. The heating rate should not exceed 200℃/h to avoid thermal stress and cracks; the cooling rate should be fast enough to prevent the re-precipitation of chromium carbide.
• Pickling and Passivation: After welding and heat treatment, the surface of the pipe and the weld seam area will still be covered with oxide scale, discoloration, and residual contaminants, which will damage the passive film and reduce the corrosion resistance of the pipe. Therefore, pickling and passivation treatment is required to restore and enhance the corrosion resistance of the pipe.

5. Manufacturing Technology of ASTM A276 TP304/304L Stainless Steel Welded Pipes

5.1 Raw Material Selection

5.2 Plate Cutting

• Shearing: This method is suitable for cutting thin-walled stainless steel plates (thickness ≤6 mm). It has the advantages of high cutting efficiency, low cost, and smooth cutting surface. The shearing equipment mainly includes hydraulic shears and mechanical shears. When shearing, the cutting edge should be sharp, and the clearance between the upper and lower cutting edges should be adjusted according to the thickness of the plate (usually 5%-10% of the plate thickness) to avoid burrs and deformation of the cutting surface.
• Plasma Cutting: This method is suitable for cutting medium-thick wall stainless steel plates (thickness 6-25 mm). It has the advantages of fast cutting speed, high cutting accuracy, and strong adaptability. The plasma cutting uses high-temperature plasma arc to melt the stainless steel plate, and then blows off the molten metal with high-pressure gas to complete the cutting. When plasma cutting, the cutting parameters (such as plasma arc current, voltage, and cutting speed) should be strictly controlled to ensure the cutting quality. The cutting surface should be smooth, free of burrs, and the cutting deviation should not exceed ±0.5 mm.
• Laser Cutting: This method is suitable for cutting high-precision stainless steel plates of various thicknesses. It has the advantages of high cutting accuracy, smooth cutting surface, and small cutting deformation. The laser cutting uses high-energy laser beam to melt and vaporize the stainless steel plate, and the cutting accuracy can reach ±0.1 mm. However, the laser cutting equipment is expensive, and the cutting cost is high, which is mainly used for cutting high-precision, small-batch pipes.

5.3 Forming

5.3.1 Roll Forming

5.3.2 Press Forming

5.4 Welding, Post-Welding Treatment and Finished Product Inspection

• Dimensional Inspection: The dimensional inspection includes the inspection of outer diameter, wall thickness, length, straightness, and roundness. The inspection methods are in accordance with Table 2. The inspection should be carried out randomly, and the sampling ratio should not be less than 5% of the total number of pipes. If unqualified products are found, the sampling ratio should be increased, and all unqualified products should be repaired or scrapped.
• Surface Quality Inspection: The surface quality inspection is mainly carried out by visual inspection and magnifying glass inspection. The inner and outer surfaces of the pipe should be smooth, free of cracks, inclusions, scratches, pits, folds, and other defects. The surface roughness should meet the requirements (hot-finished pipes ≤6.3 μm Ra, cold-finished pipes ≤1.6 μm Ra). For pipes used in food-grade and pharmaceutical applications, the surface should be inspected more strictly to ensure that there are no dead corners and easy cleaning.
• Internal Quality Inspection: The internal quality inspection mainly adopts non-destructive testing methods, including ultrasonic testing (UT), radiographic testing (RT), and magnetic particle testing (MT). For thick-walled pipes (wall thickness >15 mm), ultrasonic testing and radiographic testing must be carried out to check internal defects such as cracks, pores, and incomplete fusion. The testing results should comply with the requirements of ASTM A276 standard. For pipes used in important applications, 100% non-destructive testing should be carried out.
• Chemical Composition Inspection: The chemical composition inspection is to take samples from the finished pipes and test their chemical composition by optical emission spectroscopy (OES) or X-ray fluorescence (XRF). The test results should be within the range specified in Table 1. The sampling ratio should not be less than 3% of the total number of pipes.
• Mechanical Property Inspection: The mechanical property inspection includes tensile test, yield strength test, elongation test, hardness test, and impact toughness test. The test methods and requirements are in accordance with Table 3. The test samples should be taken from the finished pipes, and the sampling ratio should not be less than 2% of the total number of pipes. The test results must meet the minimum requirements of ASTM A276 standard.

6. Industrial Applications of ASTM A276 TP304/304L Stainless Steel Welded Pipes

6.1 Petrochemical Industry

6.2 Food Processing Industry

6.3 Pharmaceutical Industry

6.4 Water Treatment Industry

6.5 Other Industrial Fields

• Marine Engineering: In marine engineering, TP304L stainless steel welded pipes are used in ship pipelines, offshore platforms, and coastal facilities. The pipes have good corrosion resistance to seawater and marine atmospheric environment, which can avoid corrosion and damage caused by seawater and salt fog. For example, the cooling water pipeline and fuel pipeline of ships usually adopt TP304L stainless steel welded pipes.
• Chemical Industry: In the chemical industry, TP304/304L stainless steel welded pipes are used to transport various chemical media (such as acids, alkalis, salts, and organic solvents). The pipes have good corrosion resistance to most chemical media and can ensure the safe operation of the chemical production process.
• Metallurgical Industry: In the metallurgical industry, TP304 stainless steel welded pipes are used in the cooling water pipeline, steam pipeline, and flue gas pipeline of metallurgical furnaces. The pipes have high temperature resistance and corrosion resistance, which can withstand the high-temperature and corrosive environment in the metallurgical production process.
• Building Water Supply and Drainage: In modern buildings, TP304/304L stainless steel welded pipes are used in the water supply pipeline, hot water pipeline, and drainage pipeline of residential buildings, commercial buildings, and public facilities. The pipes have good hygiene performance, corrosion resistance, and beautiful appearance, which are gradually replacing traditional carbon steel pipes and plastic pipes.

7. Quality Control and Common Defects of ASTM A276 TP304/304L Stainless Steel Welded Pipes

7.1 Quality Control System

7.1.1 Raw Material Quality Control

7.1.2 Process Quality Control

• Plate Cutting Process Control: Control the cutting accuracy and surface quality of the strips. The cutting deviation of the strip width should not exceed ±0.3 mm, and the cutting surface should be smooth, free of burrs and cracks. After cutting, the strips should be inspected, and the unqualified strips should be scrapped or repaired.
• Forming Process Control: Adjust the forming machine parameters (such as roll distance, forming angle, and forming speed) to ensure the dimensional accuracy and roundness of the formed pipe. The outer diameter and wall thickness of the formed pipe should meet the requirements of ASTM A276 standard, and the roundness error should not exceed 0.5% of the nominal outer diameter. After forming, the pipe should be inspected, and the unqualified pipe should be corrected or scrapped.
• Welding Process Control: Strictly implement the welding process regulations, select reasonable welding methods and welding parameters. The welder must hold the corresponding welding qualification certificate to carry out the welding operation. During welding, the welding process parameters (such as welding current, voltage, and welding speed) should be kept stable, and the interpass temperature should be controlled below 150℃. After each layer of welding, the weld seam should be inspected to check whether there are visible defects. The unqualified weld seam should be repaired in time.
• Post-Welding Treatment Process Control: Control the post-welding cleaning, heat treatment, and pickling passivation process parameters. The post-welding cleaning should be thorough to remove welding spatter and slag; the solution heat treatment temperature and holding time should meet the requirements to ensure that the chromium carbide is fully dissolved; the pickling passivation solution concentration, temperature, and time should be controlled to avoid over-corrosion or insufficient passivation. After post-welding treatment, the pipe surface should be inspected to ensure that the surface is smooth and free of oxide scale and discoloration.

7.1.3 Finished Product Quality Control