ASTM A249 TP304/304L Welded Tubes

ASTM A249 TP304/304L welded tubes are austenitic stainless steel tubes that meet the specifications of the ASTM A249 standard. These tubes are designed for high-temperature and high-corrosion applications such as in boilers, superheaters, heat exchangers, and condensers. TP304 and TP304L are the primary grades used accounting for more than 80% of the austenitic stainless steel production. ASTM A249 TP304 has the UNS designation of S30400 while TP304L has the UNS designation of S30403. TP304 is a chromium-nickel stainless steel (18Cr-8Ni) with good corrosion resistance and mechanical properties. TP304L is a low-carbon version of TP304, which enhances its weldability and reduces the risk of carbide precipitation during welding. Based on their specific use, these tubes are also classified as: TP304/304L welded boiler tubes, TP304/304L welded heat exchanger tubes, TP304/304L superheater tubes, TP304/304L condenser tubes.

ASTM A249 Gr.TP304L welded tubes for a heat exchanger, (OD)15.88mm x (W.T)0.6mm x (L)3780mm, supplied to Georgetown, Guyana.

The ASTM A249 TP304/304L welded tubes are usually furnished with small outside diameter and light wall thickness. Despite the broader range of diameters and wall thicknesses required by the standard, the outside diameter in use is usually no greater than 3″ [76.2 mm] and the nominal wall thickness is usually no thicker than 0.12″ [3.05 mm] in engineering practice. The application of small-diameter, thin-walled stainless steel welded tubes in heat exchangers, superheaters, and boilers primarily improves heat transfer efficiency, reduces weight and cost, and provides greater design flexibility. These tubes offer a high surface area-to-volume ratio, enhancing heat transfer, and are lighter, minimizing the need for support structures and lowering installation and transportation costs. They are also cheaper to manufacture due to lower material consumption and easier processing. Their flexibility in bending and shaping meets various design needs. Additionally, thin-walled tubes provide sufficient strength for many applications without needing to withstand very high internal pressures, aligning with energy-saving and environmental goals.

Chemical Composition Requirements

The chemical composition requirements for ASTM A249 TP304 welded tubes are as follows:

• Carbon (C): Max 0.08%
• Manganese (Mn): Max 2.00%
• Phosphorus (P): Max 0.045%
• Sulfur (S): Max 0.030%
• Silicon (Si): Max 1.00%
• Chromium (Cr): 18.00-20.00%
• Nickel (Ni): 8.00-11.00%
• Iron (Fe): Balance

PMI test by using a handheld spectrometer to determine the chemical composition of ASTM A249 TP304 welded tubes.

The chemical composition requirements for ASTM A249 TP304L welded tubes are as follows::

• Carbon (C): Max 0.030%
• Manganese (Mn): Max 2.00%
• Phosphorus (P): Max 0.045%
• Sulfur (S): Max 0.030%
• Silicon (Si): Max 1.00%
• Chromium (Cr): 18.00-20.00%
• Nickel (Ni): 8.00-12.00%
• Iron (Fe): Balance

Mechanical Properties

The mechanical properties for ASTM A249 TP304 welded tubes shall be as follows:

• Tensile Strength: minimum 515 MPa (75,000 psi)
• Yield Strength (0.2% offset): minimum 205 MPa (30,000 psi)
• Elongation: minimum 35% in 2 inches (50.8 mm)
• Hardness: maximum B90 in Rockwell hardness

ASTM A249 TP304 welded tubes, (OD)38.1mm x (WT)1.2mm x (L)1820mm, bright annealed, supplied to Dubai, UAE.

The mechanical properties for ASTM A249 TP304L welded tubes shall be as follows:

• Tensile Strength: Minimum 485 MPa (70,000 psi)
• Yield Strength (0.2% offset): Minimum 170 MPa (25,000 psi)
• Elongation: Minimum 35% in 2 inches (50.8 mm)
• Hardness: maximum B90 in Rockwell hardness

Production Process

The stainless steel strips are fed to the production line for the fabrication of ASTM A249 welded tubes.

According to ASTM A249, stainless steel welded tubes shall be made from flat-rolled steel by an automatic welding process with no addition of filler metal. The specific production process for ASTM A249 TP304 and TP304L stainless steel welded tubes is as follows: (1) Select stainless steel coils that meet the ASTM A249 standard, decoil and slit them into appropriate widths. (2) Gradually bend the steel strip into a round tube shape through a series of forming rolls. This process is continuous to ensure uniform shape along the entire length of the tube. (3) Heat the edges of the tube using automatic welding processes such as Electric Resistance Welding (ERW), Tungsten Inert Gas (TIG) welding, Plasma Arc Welding (PAW), or laser welding, and apply pressure to fuse them together, forming the weld seam without adding filler metal. (4) Prior to final heat treatment, the tubes shall be subjected to a cold-drawn process. Pass the welded tubes through a series of sizing rolls to accurately adjust the outer diameter and wall thickness, ensuring the tubes meet the required dimensions.

Fabrication line for stainless steel welded tubes, involving TIG welding process.

(5) Cut the continuous lengths of the tubes into specified lengths using automatic cutting equipment. (6) Both interior and exterior surfaces of the welded tubes shall be rinsed, dried and polished prior to final heat treatment. (7) The welded tubes shall undergo solution annealing heat treatment. The tubes are heated to a specific temperature (1080°C typically for ASTM A249 Grade TP304 and TP304L) and then rapidly cooled to relieve internal stresses, enhance mechanical properties, and improve corrosion resistance. (8) Subject the tubes to rigorous inspection and testing, including chemical composition analysis, tensile testing, hardness testing, X-ray inspection, flattening test, flange test, reverse-bend test, intergranular corrosion test, visual examination, dimensional inspection. (9) Marking, packaging and shipping.