Pipe Stress Allowable: ASME B31.3 Tables
The allowable stress (S) is the maximum stress a pipe material can sustain at a given temperature per ASME B31.3 (Process Piping). Allowable stress values are listed in ASME B31.3, Table A-1 and are derived from the material’s tensile strength, yield strength, and creep properties.
How ASME B31.3 Determines Allowable Stress
ASME 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 ASME B31.3 Paragraph 323.2 must be satisfied.
- The values above are representative; always consult the latest edition of ASME B31.3, Table A-1 for design.
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