ASTM A213 TP347 & TP347H Seamless Tubes

SJZ Metalsin supplies ASTM A213 TP347 and TP347H seamless tubes for heat exchangers, boilers and superheaters. As a modified version of the classic 304 stainless steel, niobium is added to oppose chromium carbide precipitation, which means to stabilize the carbon in TP347 stainless steel. The niobium added has significant importance:

• Improved resistance to intergranular corrosion at elevated temperatures: Niobium can combine with carbon and nitrogen to form stable niobium carbides and nitrides, which act as pinning agents at grain boundaries, effectively impeding grain boundary movement and thereby reducing the occurrence of intergranular corrosion.
• Niobium is a strong carbide-forming element, exerting significant solid solution strengthening at high temperatures. Its addition can refine austenite grains and has a notable effect on the refinement of recrystallized structures. Niobium carbides and nitrides precipitate at grain boundaries and dislocations, hindering the movement of recrystallization and dislocations, suppressing grain growth, and playing a role in grain refinement.
• The addition of niobium not only enhances the high-temperature corrosion resistance of TP347 stainless steel but also significantly improves its creep and stress rupture properties at high temperatures. This is crucial for high-temperature applications, such as superheater tubes.

ASTM A213 TP347 seamless tubes, O.D.=31.75mm, W.T.=2.11mm, L=9510mm.

Similar to TP304H & TP316H, TP347H is the “H Grade” of austenitic stainless steel TP347. ASTM A213 TP347 typically contains a maximum of 0.08% carbon, while TP347H contains higher carbon content, typically ranging between 0.04% to 0.10%. The higher carbon content in TP347H contributes to improved creep resistance at elevated temperatures. Creep refers to the tendency of materials to deform slowly over time when subjected to sustained mechanical stress at high temperatures. The higher carbon content in TP347H enhances its creep resistance, allowing it to withstand higher loads and temperatures over extended periods without significant deformation. While higher carbon content can increase the risk of sensitization and intergranular corrosion, proper heat treatment and welding procedures can mitigate these issues. Post-weld heat treatment (PWHT) is often required for TP347H to minimize sensitization and restore corrosion resistance.

Chemical Composition Requirements

Mechanical Properties

ASTM A213 TP347H U-type seamless tubes for the fabrication of a superheater, supplied to Milan, Italy.

Solution Treatment Temperatures

Seamless tubes made of ASTM A213 TP347 and TP347H shall be furnished with the solution heat treatment, in which the austenitic stainless steel tubes are heated to a minimum temperature and held for a sufficient prolonged time to dissolve all the carbides in the microstructure. Then, these tubes are rapidly cooled in cold water. The minimum solutioning temperatures for ASTM A213 TP347, hot-rolled TP347H, and cold-drawn TP347H are 1900°F [1040°C], 1925°F [1050°C], and 2000°F [1100°C], respectively.