347/H Stainless Steel
Grade 347 | UNS S34700 | 1.4550
Type 347 stainless steel has slightly improved corrosion resistance over type 321 stainless steel in strongly oxidizing environments.
Type 347 is stabilized with columbium, it is preferable for aqueous and low temperature environments due to its good resistance to intergranular attack.
Both 347 and 321 offer good resistance to polythionic acid stress corrosion cracking, encountered in oil refineries.
The high temperature oxidation resistance of 347 is similar to that of 304 stainless steel. Useful to 1500°F.
Often in many product forms, the grain size and carbon content can meet both the 347S and 347H requirements.
Appropriate weld fillers are AWS ER347 bare wire and E347 covered electrodes.
•Good creep strength up to 1500°F
•Maintains good corrosion resistance in applications where the temperature is between 800°F and 1500°F.
•Good resistance to intergranular corrosion in the as welded condition.
As with most steel plate products a number of different designations are used for these steels. The most common are:
•Type 347 1.4550 (EN Steel Number) S34700 (UNS)
Typical industrial sectors:
•Fluid catalytic cracking units (FCC)
•Recuperator tube sheets, shell, supports
•Especially where temperatures exceed 550°F and resistance to sulfidation is needed
•Fired heater tubes
•Distributor trays and thermowells
•Equipment in and around reactors (good resistance to polythionic acid)