ASTM A312 Stainless Steel Pipe Grades

ASTM A312 stainless steel pipe grades define the chemistry, mechanical properties, and manufacturing requirements for austenitic stainless steel pipes used in corrosive, high-temperature, and cryogenic service. The specification covers seamless, welded, and heavily cold-worked pipe in grades ranging from the standard 304 and 316 families to stabilized grades (321, 347) and high-temperature grades (310S). Selecting the correct A312 grade is fundamental to corrosion resistance, weldability, and long-term reliability in process piping systems.

Grade Comparison Table

Grade	UNS	Cr (%)	Ni (%)	Mo (%)	C (max %)	Stabilizer	Key Feature
TP304	S30400	18-20	8-11	-	0.08	-	Standard austenitic grade
TP304L	S30403	18-20	8-12	-	0.035	-	Low carbon for weld corrosion resistance
TP304H	S30409	18-20	8-11	-	0.04-0.10	-	High carbon for creep strength
TP316	S31600	16-18	10-14	2-3	0.08	-	Mo for pitting resistance
TP316L	S31603	16-18	10-14	2-3	0.035	-	Low carbon + Mo
TP321	S32100	17-19	9-12	-	0.08	Ti (5xC min)	Ti-stabilized against sensitization
TP321H	S32109	17-19	9-12	-	0.04-0.10	Ti	High carbon + Ti stabilized
TP347	S34700	17-19	9-13	-	0.08	Nb (10xC min)	Nb-stabilized against sensitization
TP310S	S31008	24-26	19-22	-	0.08	-	High-temperature oxidation resistance

Mechanical Properties by Grade

Grade	Yield Strength (min MPa)	Tensile Strength (min MPa)	Elongation (min %)	Hardness (max HBW)
TP304	205	515	35	183
TP304L	170	485	35	183
TP316	205	515	35	183
TP316L	170	485	35	183
TP321	205	515	35	183
TP347	205	515	35	183
TP310S	205	515	35	183

Grade Selection Guide

TP304/304L: The default choice for general corrosive service where chloride concentrations are low. TP304L is preferred when the pipe will be welded, as its low carbon content prevents intergranular corrosion in the heat-affected zone. Most mills supply dual-certified 304/304L pipe.

TP316/316L: Required when the service fluid contains chlorides (seawater, brine, brackish water) or when higher pitting resistance is needed. The 2-3% molybdenum content provides significantly better resistance to pitting and crevice corrosion than 304.

TP321/321H: Specified for continuous service at 425-815 degC where sensitization resistance is needed but low-carbon (“L”) grades lack sufficient creep strength. The titanium stabilizer binds carbon before it can precipitate as chromium carbides.

TP347: Similar to TP321 but uses niobium as the stabilizer. Preferred in some refinery applications and where the weld procedure specification calls for matching Nb-stabilized filler metal.

TP310S: Selected for high-temperature oxidation resistance up to 1,100 degC. Used in furnace tubes, reformer pigtails, and flare tips.

Manufacturing Methods per A312

Method	Description	Typical Application
Seamless	Hot worked and cold finished from solid billet	High-pressure, critical service
Straight-seam welded	TIG, plasma, or laser welded from strip	General process piping, cost-effective
Heavily cold-worked	Cold-reduced to final dimensions	Precision tubing, instrumentation

All welded pipes under A312 must have the weld area solution annealed (1040 degC minimum for 304/316) and pass a hydrostatic test or eddy current test.

Pro Tip

Dual-certified pipe (e.g., TP304/304L or TP316/316L) meets the chemistry and mechanical requirements of both the standard and low-carbon grades. This provides procurement flexibility because the same pipe can be used in both welded and unwelded applications. Verify dual certification on the mill test certificate before installation.

Read the full guide to stainless steel pipes