At a Glance
All Grades
304/316/321/347 + H/L
Condition
Solution Annealed
Scope
ASTM A312 covers seamless, welded, and heavily cold worked austenitic stainless steel pipe for high-temperature and general corrosive service. Unlike the carbon steel pipe specs (A106, A53), A312 covers both seamless and welded construction under one specification — the manufacturing method is a line-item selection on the purchase order, not a separate spec.
All A312 pipe must be furnished in the solution-annealed condition — heated above 1900°F and rapidly quenched to dissolve carbides and restore corrosion resistance. This is a mandatory requirement, not optional.
Grade Families
Standard
TP304TP316
The workhorse grades. Specify these when general corrosion resistance is needed and welding is not a primary concern, or when post-weld solution anneal is possible.
Low Carbon (L)
TP304LTP316L
Low carbon variants. The 'L' stands for Low Carbon — NOT low temperature. Prevents sensitization in the HAZ during welding. The most common grades for welded fabrication.
High Carbon (H)
TP304HTP316H
High carbon variants for elevated-temperature service. Better creep strength above 900°F. Cannot be dual certified with L grades — H and L are mutually exclusive.
Stabilized
TP321TP347
Stabilized grades for high-temperature cycling service. Titanium (321) or Niobium (347) ties up carbon to prevent sensitization without relying on low carbon content.
Critical Points
"L" stands for Low Carbon — not Low Temperature. TP304L and TP316L are specified for welding, not cold service. The low carbon content (0.035% max vs 0.08% max) prevents sensitization in the heat-affected zone during welding. Austenitic stainless steel as a family is inherently excellent at low temperatures — any A312 grade works at cryogenic temperatures without a special designation.
H and L grades are mutually exclusive. You cannot dual certify TP304H and TP304L — their carbon ranges do not overlap. TP304H requires 0.04% minimum carbon; TP304L requires 0.035% maximum. When a drawing says "304H/304L," it is an error — clarify with the engineer before ordering.
304/304L dual certification is the commercial standard. Most 304 pipe in the market is ordered and stocked as dual-certified TP304/TP304L — the material meets both the chemistry and mechanical requirements of both grades simultaneously and is marked accordingly. Same applies to 316/316L.
Solution anneal is mandatory. All A312 pipe must be solution annealed before shipment. Pipe that has been welded without subsequent solution anneal is not A312-compliant. For field-welded systems where re-annealing is impractical, specify L grades to protect the HAZ without needing post-weld heat treatment.