Pipe Material Selection
Corrosion first, temperature second, pressure third, cost last — working through the four specifications that cover most steel process piping.
- A106
- Seamless carbon, high temperature
- A53
- General service carbon, welded or seamless
- A312
- Austenitic stainless
- A335
- Chrome-moly alloy, creep range
Short answer. Four specifications cover most steel process piping. A53 is general service carbon steel for utilities. A106 is seamless carbon steel for process and high temperature — the default for hydrocarbons and steam. A312 is austenitic stainless for corrosion resistance and for temperatures above what carbon steel tolerates. A335 is chrome-moly alloy for the creep range, roughly 800 °F and up.
The decision in order
Material selection runs corrosion first, then temperature, then pressure, then cost — in that order, because the first three are constraints and only the last is a preference.
| Question | If yes | Leads to |
|---|---|---|
| Is the fluid corrosive to carbon steel? | Chlorides, acids, oxygenated water, sour service | Stainless (A312), duplex (A790), or lined/clad carbon steel |
| Is the design temperature above 800 °F? | Carbon steel oxidises and can graphitise | Chrome-moly (A335 P11/P22/P91) or stainless (A312) |
| Is the design temperature below −20 °F? | Ordinary carbon steel is brittle | Impact-tested carbon (A333 Gr 6) or austenitic stainless |
| Is the service hydrocarbon, steam or process? | Needs a seamless, tested, high-temperature grade | A106 Gr B |
| Is it water, air, or a fire main? | General service is sufficient | A53 Gr B, galvanised where appropriate |
| Is product purity critical? | Contamination from iron oxide is unacceptable | A312 stainless, often 316L with a specified finish |
Constraints first. Cost only decides between options that have already satisfied corrosion, temperature and pressure.
The four specifications
| Specification | Full scope | Manufacture | Typical use |
|---|---|---|---|
| ASTM A53 | Pipe, black and hot-dipped zinc-coated, welded and seamless | Type S seamless, Type E ERW, Type F furnace butt welded | Water, air, low-pressure steam, fire protection, structural and sleeves |
| ASTM A106 | Seamless carbon steel pipe for high-temperature service | Seamless only | Process piping, steam, refinery and power generation — the carbon steel default in process plant |
| ASTM A312 | Seamless, welded and heavily cold worked austenitic stainless pipe | Seamless and welded grades, each separately designated | Corrosive service, high purity, cryogenic, and sustained high temperature |
| ASTM A335 | Seamless ferritic alloy steel pipe for high-temperature service | Seamless only | Creep range service: heaters, high-energy steam, hydroprocessing |
Grades and strengths
| Specification | Form | Tensile min | Yield min | Temperature range | Notes |
|---|---|---|---|---|---|
| ASTM A53 Gr B | Pipe | 60 ksi | 35 ksi | -20 to 750 °F | Seamless or ERW. Ordinary utility service — air, water, steam, gas. Not impact-tested. |
| ASTM A106 Gr B | Pipe | 60 ksi | 35 ksi | -20 to 800 °F | The workhorse seamless carbon steel pipe for high-temperature process service. |
| ASTM A106 Gr C | Pipe | 70 ksi | 40 ksi | -20 to 800 °F | Higher carbon than Gr B; more strength, harder to weld. |
| ASTM A333 Gr 6 | Pipe | 60 ksi | 35 ksi | -50 to 650 °F | Impact-tested carbon steel for low-temperature service. The standard cryo-adjacent carbon pipe. |
| ASTM A335 P11 | Pipe | 60 ksi | 30 ksi | up to 1100 °F | 1¼Cr-½Mo. Steam and hydrocarbon service in the creep range. |
| ASTM A335 P22 | Pipe | 60 ksi | 30 ksi | up to 1100 °F | 2¼Cr-1Mo. Refinery heater and high-temperature hydrogen service. |
| ASTM A335 P91 | Pipe | 85 ksi | 60 ksi | up to 1200 °F | 9Cr-1Mo-V. Modern high-energy steam. Requires strict PWHT control. |
| ASTM A312 TP304 | Pipe | 75 ksi | 30 ksi | -425 to 1500 °F | General-purpose austenitic stainless. Sensitises if welded and held at 800-1500 °F. |
| ASTM A312 TP316L | Pipe | 70 ksi | 25 ksi | -425 to 850 °F | Low-carbon 316. The default stainless for welded chemical process piping. |
| ASTM A790 S31803 | Pipe | 90 ksi | 65 ksi | -60 to 600 °F | 2205 duplex. Roughly twice the yield of 316L with far better chloride SCC resistance. |
Strengths are specified minimums in ksi. 1 ksi = 1000 psi = 6.895 MPa.
Temperature is the hardest constraint
Pressure can be answered with more wall. Temperature usually cannot, because the limits are metallurgical rather than structural.
| Temperature range | Material | Governing concern |
|---|---|---|
| Below −50 °F | A312 austenitic stainless | Austenitic stainless stays tough to −425 °F; ferritic steels do not. |
| −50 to −20 °F | A333 Gr 6 | Impact-tested carbon steel with a guaranteed Charpy value. |
| −20 to 750 °F | A53 or A106 | Ordinary carbon steel range. A53 stops around 750 °F, A106 around 800 °F. |
| 750 to 1000 °F | A335 P11 or P22 | Carbon steel graphitises and oxidises; chrome-moly resists both and has creep strength. |
| 1000 to 1200 °F | A335 P91, A312 TP304H/347H | Creep governs entirely. P91 needs strict PWHT control. |
| Above 1200 °F | Austenitic stainless and nickel alloys | Beyond the ferritic alloys; oxidation and creep both severe. |
Ranges are indicative. The design code's allowable stress tables and the owner's specification govern.
Corrosion allowance
Carbon steel in a corrosive service is normally given a corrosion allowance — typically 1/16 in (1.6 mm), sometimes 1/8 in for aggressive duty — added to the pressure design thickness. Stainless in clean service is usually given none, which is the reason thin-wall S-schedule stainless is viable while thin-wall carbon steel generally is not.
Watch the economics here. A corrosion allowance that pushes carbon steel up two schedules can cost more than specifying stainless with no allowance at all, particularly in small bore.
Things that catch people out
- Galvanised pipe cannot be welded without removing the zinc first — the fumes are toxic and the weld is poor. Galvanised systems are threaded or flanged.
- Stainless expands 40–50% more than carbon steel. Substituting materials invalidates the flexibility analysis.
- Austenitic stainless sensitises if held between 800 and 1500 °F, which welding does. Use L grades for welded assemblies.
- P91 is unforgiving. Its properties depend entirely on correct post-weld heat treatment; a mis-heat-treated P91 weld is weaker than the carbon steel it replaced.
- Dissimilar welds are galvanic couples. Stainless welded to carbon steel in a wet service will corrode the carbon steel preferentially.
See also: A106 vs A53 · carbon vs stainless · 304 vs 316 · full material grade tables.
Common questions
When should I use A106 instead of A53?
For process piping, steam and anything above roughly 400 °F. A106 is seamless, has controlled chemistry for elevated temperature, and is mechanically tested. A53 is a general service specification.
What pipe material is used above 800 °F?
Chrome-moly alloy to ASTM A335 — P11 or P22 through about 1100 °F and P91 to 1200 °F — or austenitic stainless to A312. Carbon steel is limited by oxidation and graphitisation rather than by its pressure rating.
What is the standard low-temperature pipe material?
ASTM A333 Grade 6 for carbon steel down to −50 °F, and austenitic stainless below that — 304 and 316 stay tough to −425 °F.
How much corrosion allowance should carbon steel pipe have?
1/16 in (1.6 mm) is the usual default, with 1/8 in for aggressive service. It is added to the pressure design thickness before mill tolerance is applied.
Can I substitute stainless for carbon steel pipe?
Not without rechecking the design. Stainless has a lower allowable stress at ambient, expands 40–50% more, and changes the flexibility analysis and support loads.