347H Stainless Steel is the higher carbon (0.04 – 0.10) version of the alloy. It was developed for enhanced creep resistance and for higher strength at temperatures above 1000°F (537°C). In most instances, the carbon content of the pipe enables dual certification. 347H Stainless Steel Pipe is stabilized stainless steel plate which offers as its main advantage an excellent resistance to intergranular corrosion following exposure to temperatures in the chromium carbide precipitation range from 800 to 1500°F (427 to 816°C). Alloy 347 stainless steel plate is stabilized by the addition of columbium and tantalum. The steel has excellent forming and welding qualities and excellent toughness even at cryogenic temperatures.

Benefits of 347H Stainless Steel

● Higher creep stress and rupture properties when compared with 304

● Ideal for high temperature service

● Overcomes sensitization and intergranular corrosion concerns

● Can be used in elevated temperature applications for ASME Boiler and Pressure Vessel Code applications

● Due to stabilisation the material offers better overall corrosion resistance when compared to 304/304L

● Excellent mechanical properties

● A high carbon version (347H) is also available

Resistance to corrosion of 347H Stainless Steel

General corrosion Alloys 321 and 347 offer similar resistance to general, overall corrosion as the unstabilized chromium nickels Alloy 304. Heating for long periods of time in the chromium carbide precipitation range may affect the general resistance of Alloys 321 and 347 in severe corrosive media.

In most environments, both alloys will show similar corrosion resistance; however, Alloy 321 in the annealed condition is somewhat less resistant to general corrosion in strongly oxidizing environments than annealed Alloy 347. For this reason, Alloy 347 is preferable for aqueous and other low temperature environments. Exposure in the 8000F to 15000F (4270C to 8160C) temperature range lowers the overall corrosion resistance of Alloy 321 to a much greater extent than Alloy 347. Alloy 347 is used primarily in high temperature applications where high resistance to sensitization is essential, thereby preventing intergranular corrosion at lower temperatures.

Heat Treatment of 347H Stainless Steel

The annealing temperature range for Alloys 321 and 347 is 1800 to 20000F (928 to 10930C). While the primary purpose of annealing is to obtain softness and high ductility, these steels may also be stress relief annealed within the carbide precipitation range 800 to 15000F (427 to 8160C), without any danger of subsequent intergranular corrosion. Relieving strains by annealing for only a few hours in the 800 to 15000F (427 to 8160C) range will not cause any noticeable lowering in the general corrosion resistance, although prolonged heating within this range does tend to lower the general corrosion resistance to some extent. As emphasized, however, annealing in the 800 to 15000F (427 to 8160C) temperature range does not result in a susceptibility to intergranular attack.For maximum ductility, the higher annealing range of 1800 to 20000F (928 to 10930C) is recommended.