Difference Between Stainless Steel 321 and 347

ASTM A213 321 321H 347 347H Chemical Composition:

Grade	321	321H	347	347H
UNS Designation	S32100	S32109	S34700	S34709
Carbon (C) Max.	0.08	0.04–0.10	0.08	0.04-0.10
Manganese (Mn) Max.	2.00	2.00	2.00	2.00
Phosphorous (P) Max.	0.045	0.045	0.04	0.04
Sulphur (S) Max.	0.03	0.03	0.03	0.03
Silicon (Si) Max.	1.00	1.00	0.75	0.74
Chromium (Cr)	17.0–20.0	17.0–20.0	17.0–20.0	17.0–20.0
Nickel (Ni)	9.0–12.0	9.0–12.0	9.0–13.0	9.0–13.0
Molybdenum (Mo)	–	–	–	–
Nitrogen (N)	–	–	–	–
Iron (Fe)	Bal.	Bal.	Bal.	Bal.
Other Elements	Ti=5(C+N) to 0.70%	Ti=4(C+N) to 0.70%	Cb+Ta=10xC-1.0	Cb+Ta=10xC-1.0

A limitation with 321 is that titanium does not transfer well across a high temperature arc, so is not recommended as a welding consumable. In this case grade 347 is preferred – the niobium performs the same carbide stabilisation task but can be transferred across a welding arc. Grade 347 is therefore the standard consumable for welding 321. Grade 347 is only occasionally used as parent plate material.

Like other austenitic grades, 321 and 347 have excellent forming and welding characteristics, are readily brake or roll formed and have outstanding welding characteristics. Post-weld annealing is not required. They also have excellent toughness, even down to cryogenic temperatures. Grade 321 does not polish well, so is not recommended for decorative applications.

TP321 Stainless Steel Tubes

Features:

TP321 is a stabilized stainless steel that offers as its main advantage an excellent resistance to intergranular corrosion following exposure to temperature in the chromium carbide precipitation range from 800 °F to 1500°F (427°C to 816°C). Alloy 321 stainless steel tubing is stabilized against chromium carbide formation by the addition of titanium.

TP347H Stainless Steel Tube:

Features:
It is a stable austenitic heat-strength steel. It has good heat strength and resistance to intergranular corrosion, good welding performance, and good corrosion resistance in alkali, seawater and various acids.347H and 347HFG in higher elevated temperature allowable stresses for these stabilized alloys for ASME Boiler and Pressure Vessel Code applications.

Application:
Heat exchangers for large boiler superheater tubes, reheater tubes, steam lines and petrochemicals. The allowable oxidation temperature in boiler tubes is 750 °C.