My response is based on the assumption that ASME Section I is the governing code. You will need to verify this with the Jurisdictional authority where the installation is located.

ASME Section I design requires that the stress tables in ASME Section IID be used as the basis for determining the allowable wall thickness of materials (based on the MAWP at the maximum temperature).

You provided either operational parameters or design parameters. For the sake of this response, I'll assume they are design: MAWP 256psi , Max temperature 842F. If they are actually operating parameters, the results listed below are not valid (the actual results will be more restrictive).

Table 1A of Section IID (2001 edition, 2003 addenda) allows the use of SA106B, in Section I applications, at temperatures up to 1000F. Furthermore, at a temperature of 850F, the stress value allowed for calculating wall thickness is 8,700psi. It certainly appears that the material is suitable for the existing conditions.

There are some notes that may or may not apply to your situation. The best advice is to ask an engineer familiar with ASME codes to look into your specific situation.

Good luck.

Charles Hall

I did some more research after my initial posting and have the following additional information to offer.

ASME B31.1, Power Piping imposes more limiting restrictions on the use of carbon steel materials for piping. In short, for steam piping applications (not including discharge piping from relief valves), carbon steel material may not be used at temperatures exceeding 800F (general note [e] of Table A-1).

I have to admit it's the first time I have looked this closely at B31.1. In the past I have relied almost exclusively on Section IID for design information.

Charles Hall