Pipe Stress Allowable: American Standard B31.3 Tables
The allowable stress (S) is the maximum stress a pipe material can sustain at a given temperature per American Standard B31.3 (Process Piping). Allowable stress values are listed in American Standard B31.3, Table A-1 and are derived from the material’s tensile strength, yield strength, and creep properties.
How American Standard B31.3 Determines Allowable Stress
American Standard B31.3 defines the basic allowable stress as the lowest of:
- 1/3 of the tensile strength at room temperature or at temperature
- 2/3 of the yield strength at room temperature or at temperature
- 100% of the average stress for a creep rate of 0.01%/1000 hours
- 67% of the average stress to cause rupture in 100,000 hours
Below the creep range, tensile and yield criteria govern. Above approximately 370 deg C for carbon steel, creep controls the allowable stress.
Allowable Stress Table: Carbon Steel Pipes
| Temperature | A106 Gr. B / A53 Gr. B | A335 P11 (1-1/4Cr-1/2Mo) | A335 P22 (2-1/4Cr-1Mo) |
|---|---|---|---|
| 38 deg C (100 deg F) | 138 MPa (20,000 psi) | 138 MPa (20,000 psi) | 138 MPa (20,000 psi) |
| 100 deg C (212 deg F) | 138 MPa (20,000 psi) | 138 MPa (20,000 psi) | 138 MPa (20,000 psi) |
| 200 deg C (392 deg F) | 134 MPa (19,400 psi) | 138 MPa (20,000 psi) | 138 MPa (20,000 psi) |
| 300 deg C (572 deg F) | 121 MPa (17,500 psi) | 131 MPa (19,000 psi) | 131 MPa (19,000 psi) |
| 400 deg C (752 deg F) | 103 MPa (14,900 psi) | 117 MPa (17,000 psi) | 117 MPa (17,000 psi) |
| 450 deg C (842 deg F) | 72 MPa (10,500 psi) | 107 MPa (15,500 psi) | 107 MPa (15,500 psi) |
| 500 deg C (932 deg F) | Not recommended | 79 MPa (11,500 psi) | 86 MPa (12,500 psi) |
| 550 deg C (1022 deg F) | Not recommended | 46 MPa (6,700 psi) | 55 MPa (8,000 psi) |
Allowable Stress Table: Stainless Steel Pipes
| Temperature | A312 TP304/304L | A312 TP316/316L | A312 TP321 |
|---|---|---|---|
| 38 deg C (100 deg F) | 138 MPa (20,000 psi) | 138 MPa (20,000 psi) | 138 MPa (20,000 psi) |
| 200 deg C (392 deg F) | 110 MPa (15,900 psi) | 115 MPa (16,600 psi) | 113 MPa (16,300 psi) |
| 300 deg C (572 deg F) | 97 MPa (14,000 psi) | 103 MPa (14,900 psi) | 101 MPa (14,700 psi) |
| 400 deg C (752 deg F) | 88 MPa (12,800 psi) | 95 MPa (13,800 psi) | 93 MPa (13,500 psi) |
| 500 deg C (932 deg F) | 81 MPa (11,800 psi) | 88 MPa (12,800 psi) | 86 MPa (12,500 psi) |
| 600 deg C (1112 deg F) | 69 MPa (10,000 psi) | 76 MPa (11,000 psi) | 74 MPa (10,700 psi) |
| 700 deg C (1292 deg F) | 41 MPa (6,000 psi) | 46 MPa (6,700 psi) | 44 MPa (6,400 psi) |
Key Points
- Carbon steel (A106 Gr. B) loses strength rapidly above 400 deg C. Alloy steels (P11, P22) and stainless steels maintain higher allowable stresses at elevated temperatures.
- The weld joint factor (E) and weld strength reduction factor (W) are multiplied by the allowable stress in the wall thickness calculation. For seamless pipe, E = 1.0.
- For cryogenic service (below -29 deg C), impact testing per American Standard B31.3 Paragraph 323.2 must be satisfied.
- The values above are representative; always consult the latest edition of American Standard B31.3, Table A-1 for design.
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