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# ASTM A335 P91 - High Pressure Piping Design, B31.3, Chapter IX

## ASTM A335 P91 - High Pressure Piping Design, B31.3, Chapter IX

(OP)
I'm trying to determine the wall thickness of a pipe that has a design pressure of 15,000 psi at 700 F.
The specified material is ASTM A335 P91. I have to use ASME B31.3 chapter IX (defined by the owner). The problem is that ASTM A 335 P91 is listed only in Appendix A. Can I use the allowable stress from Table A-1 in the equations to calculate the required wall thickness in paragraph K304.1.2 (chapter IX)?

### RE: ASTM A335 P91 - High Pressure Piping Design, B31.3, Chapter IX

See K302.2.2(b) "Piping components that do not have allowable stresses or P-T ratings shall be qualified for pressure design as required by K304.7.2"

----------------------------------
Not making a decision is a decision in itself

### RE: ASTM A335 P91 - High Pressure Piping Design, B31.3, Chapter IX

Short: no. For chapter IX, you need to use allowable stresses from table K-1.

Huub
- You never get what you expect, you only get what you inspect.

### RE: ASTM A335 P91 - High Pressure Piping Design, B31.3, Chapter IX

(OP)
Thank you all very much for your answers. Therefore, as a conclusion, if I use ASTM A335 P91, I´ll have to calculate the allowable stress values at design temperature not exceed the lower of two-thirds of SY and two thirds of Syt. But I think there is a reason for ASME not to use ASTM A335 P91 in table K-1. Does anyone know why?

### RE: ASTM A335 P91 - High Pressure Piping Design, B31.3, Chapter IX

The reason why P91 may not be in table K-1; we don't know. At least I don't. Code committee consists of volunteers that together try to improve the code. Sometimes, they forget something, and sometimes, people don't ask for certain materials to become a code listed materials. What ever the reason, one may guess.

As for the 2/3 on yield; table K-1 has its own way to dervie the allowable stresses listed in table K-1; review K302.3.2.

Huub
- You never get what you expect, you only get what you inspect.

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