Material Reference
Stainless Steel Flanges & Fittings
Stainless steel earns its place wherever carbon corrodes too quickly, hygiene matters, or temperatures sit high enough that chromium oxide stability becomes a real design factor. The ASTM A182 family covers forged stainless flanges and fittings, with 304/304L and 316/316L as the everyday austenitic defaults and a deeper bench of grades for sensitization, elevated temperature, and chloride duty.
Austenitic Grades - The Workhorses
Roughly 70 percent of the stainless flanges and fittings in industrial service are austenitic 18-8 family material, and the bulk of that is 304 or 316. Three grade tiers cover the common service envelopes: L grades for welded service at standard temperature, standard grades for general use, and H gradesfor elevated temperature where creep strength and carbon stability matter.
Most A182 stainless is supplied dual-certified to both the standard and L grade (e.g. F304/F304L stamped to the same forging), which keeps procurement simple. H grades are a separate order with their own UNS number and their own carbon and grain-size requirements.
F304 / F304L (UNS S30400 / S30403)
The general purpose austenitic, typically supplied dual-certified F304/304L. The L variant caps carbon below 0.030 percent to protect against chromium carbide precipitation in weld heat-affected zones. Good corrosion resistance in mild atmospheric, fresh water, and most organic chemistry. Used in food and beverage process lines, pharmaceutical utility systems, low-pressure refinery and chemical service, and architectural piping. Limited in chloride-rich environments where pitting begins to appear.
F316 / F316L (UNS S31600 / S31603)
Typically supplied dual-certified F316/316L. The molybdenum addition (roughly 2 to 3 percent Mo) buys real chloride and pitting resistance. The default stainless in chemical processing, marine atmospheric exposure, brackish service, and seawater-adjacent piping that does not warrant the cost of duplex. 316L is the typical spec when welding is involved.
F304H / F316H (UNS S30409 / S31609)
H grades carry a carbon floor (0.04 to 0.10 percent) and a controlled grain size. ASME B31.3 and the relevant pressure-vessel codes require H grades for design temperatures above approximately 800F, where the additional carbon and grain-size control give predictable creep strength. Low-carbon L grades are explicitly disallowed above that threshold. Specify F304H or F316H for elevated-temperature steam, refinery hydrocarbon service, and FCC and reformer piping.
F321 / F321H (UNS S32100 / S32109) - Titanium Stabilized
Conventional 304 is vulnerable to sensitization when service temperature sits in the 800F to 1500F band. F321 adds titanium to tie up carbon and prevent chromium carbide formation, keeping grain-boundary corrosion in check at temperature. For elevated-temperature service above roughly 1000F where creep matters, F321H is the required variant - it carries the same carbon and grain-size controls as the other H grades. Common on high-temperature exhaust, expansion joints, and refining heater service.
F347 / F347H (UNS S34700 / S34709) - Niobium Stabilized
The niobium (columbium) stabilized counterpart to F321. Same sensitization protection mechanism, often preferred where weldability and post-weld heat treatment behavior favor niobium over titanium. F347H carries the elevated carbon and grain-size requirements for service above approximately 1000F. Used in refinery reformer service, high-temperature hydrogen, and elevated-temperature process piping where stabilized austenitic chemistry is specified.
F310 / F310S (UNS S31000 / S31008)
A 25Cr-20Ni austenitic with substantially higher chromium and nickel than 304 or 316. The higher chromium gives better scaling resistance at sustained high temperatures, pushing usable service up toward 2000F in oxidizing atmospheres. Used on furnace and heat-treatment fixtures, radiant tubes, and high-temperature exhaust components. F310S is the low-carbon variant for welding.
F317L (UNS S31703)
A higher-molybdenum (3 to 4 percent Mo) variant of 316L, used where 316L is marginal on chloride pitting but the jump to duplex or 6Mo is not warranted. Common on flue gas desulfurization, pulp bleaching, and chloride-bearing aqueous service.
Carbon and temperature note. Standard and L grades are not interchangeable with H grades above approximately 800F. ASME B31.3 and the pressure vessel codes specify minimum carbon for elevated service to provide creep strength. If a line list calls out service above 800F, confirm whether the spec requires F304H, F316H, F321H, or F347H rather than the standard or L variant.
Ferritic And Martensitic - The Other Side Of The Family
Ferritic grades (the 400-series like 430) and martensitic grades (410, 420) show up far less often in flange and fitting work than the austenitic 300-series. They are magnetic, generally lower in nickel, and have different welding and toughness profiles. Most flange specifications in process and pipeline service stay inside the A182 austenitic family for predictability and weldability.
Ferritic and martensitic grades are available when a project calls for them, but the design conversation usually starts with why a 300-series austenitic will not work. Texas Flange can run the tradeoffs on request.
ASTM A182 - The Spec Behind The Grades
ASTM A182 is the umbrella specification for forged or rolled alloy and stainless steel pipe flanges, forged fittings, and valves intended for high-temperature service. The F-prefix grades (F304, F316, F321, F11, F22, F91, and so on) all live under A182.
When a line list calls out "A182 F316L," it is specifying both the manufacturing route (forged or rolled to A182 chemistry, mechanical, and heat-treatment requirements) and the grade. Mill test reports trace back to that combined requirement.
When To Pick Stainless
Stainless earns its premium in four scenarios. First, corrosive chemistry where carbon would not survive the design life. Second, hygienic service in food, beverage, dairy, and pharmaceutical lines where contamination and cleanability matter as much as pressure containment. Third, elevated temperature where chromium oxide stability beats iron oxide. Fourth, architectural or appearance-driven installations.
See our work in food and beverage and chemical processing for typical project profiles.
The Honest Trade-Offs
Stainless is more expensive than carbon, usually by a factor of three to five on a per-flange basis. It also has lower allowable stresses than carbon at room temperature, which means heavier wall in some pressure-temperature combinations. And it is more sensitive to chloride stress cracking than many designers realize - even 316 has limits, which is why duplex exists.
For chloride service that pushes past 316, see our exotic alloys page, which covers duplex and the nickel-rich grades.
Need a Stainless Quote?
304, 316, 321, 347, 310, 317L, or H grades in any A182 form. Send the line list and the schedule to Texas Flange for pricing and availability.