The Allowable Stress – Temperature Chart for ASTM A335 P91
P91 is one of the steel grades specified by ASTM A335, the standard specification for seamless ferritic alloy steel pipe for high-temperature service. The maximum allowable stress in different temperature ranges shall be determined by ASME B31.1 and ASME B31.3 respectively.
A 660MW combined-cycle power plant in which the A335 P91 seamless pipes were introduced by Metals-Piping.
1. ASME B31.1: Allowable Stress – Temperature of ASTM A335 P91
| *Temp. °F | -20-100 | 200 | 300 | 400 | 500 | 600 | 650 | 700 | 750 |
| *AS-I, ksi | 24.3 | 24.3 | 24.3 | 24.2 | 24.1 | 23.7 | 23.4 | 22.9 | 22.2 |
| *AS-II, ksi | 24.3 | 24.3 | 24.3 | 24.2 | 24.1 | 23.7 | 23.4 | 22.9 | 22.2 |
| *Temp. °F | 800 | 850 | 900 | 950 | 1000 | 1050 | 1100 | 1150 | 1200 |
| *AS-I, ksi | 21.3 | 20.3 | 19.1 | 17.8 | 16.3 | 14.0 | 10.3 | 7.0 | 4.3 |
| *AS-II, ksi | 21.3 | 20.3 | 19.1 | 17.8 | 16.3 | 12.9 | 9.6 | 7.0 | 4.3 |
*AS-I: the maximum allowable stress for thickness less than 3 inches.
*AS-II: the maximum allowable stress for thickness 3 inches or greater.
*The tabulated values are applicable to ASTM A335 P91 pipes used for power piping construction as per ASME B31.1.
2. ASME B31.3: Allowable Stress – Temperature of ASTM A335 P91
| *Temp. °F | -20~100 | 200 | 300 | 400 | 500 | 600 | 650 | 700 | 750 |
| *BS, ksi | 28.3 | 28.3 | 28.3 | 28.2 | 28.1 | 27.7 | 27.3 | 26.7 | 25.9 |
| *Temp. °F | 800 | 850 | 900 | 950 | 1000 | 1050 | 1100 | 1150 | 1200 |
| *BS, ksi | 24.9 | 23.7 | 22.3 | 20.7 | 18.0 | 14.0 | 10.3 | 7.0 | 4.3 |
*BS: the basic allowable stress for thickness no greater than 3 inches.
*The tabulated values are applicable to both A335 P91 & A691 P91 pipes used for process piping construction as per ASME B31.3.
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