Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


P9 / P91 in ASME BPV

P9 / P91 in ASME BPV

P9 / P91 in ASME BPV

Just a question out of curiosity of something I noticed today. Does have no effect for me personal as Im not using P91 grades for anything.
- ASTM A 335 P91 has UNS K91560
- in ASME BPV II-A 2017, ASME SA 335 P91 has UNS K91560
- in ASME BPV II-D 2017, ASME SA-335 P91 has UNS K90901.
The same seems to hold for other product forms of grade 91 (like flange, fitting, plate) as well. Is this a mistake in the code, or is there something Im missing?

Also, why is P9 called UNS S50400 in SA335 of II-A? Another mistake? This one is found both in the ASTM standard, as well as in II-A, but not in II-D.

RE: P9 / P91 in ASME BPV

I checked my files, and interestingly in A/SA 335-99 (2001 ASME Code edition), the UNS listed for Grade 91 was K90901. Even T91 tubing under A/SA-213 in the 2010 edition of Part A was listed as UNS K90901. However, A/SA 335 pipe specification, the UNS was revised to K91560.

Upon closer review, the chemistry was slightly modified from the original Grade 91 pipe based on below;
Grade P91 in 2010
N 0.030–0.070
Ni 0.40 max.
Al 0.02 max.
Cb 0.06–0.10
Ti 0.01 max.
Zr 0.01 max.

Grade P91 in 2001
N 0.030–0.070
Ni 0.40 max.
Al 0.04 max.
Cb 0.06–0.10
So, nothing needed other than to pay close attention to the A/SA edition when ordering Grade 91 pipe.
For tubing, there was no UNS assigned in 2004 edition of the code.

RE: P9 / P91 in ASME BPV

Regarding the P9 question;

The A/SA 335 specification in 2001 edition had the UNS listed as K90941
Later edition at 2010, the A/SA 335 revised P9 to UNS K50400

Lets look closer;
Note in 2010 edition
(Identical with ASTM Specification A 335/A 335M-06 except for the addition of hardness requirements for P23 and P911 in 9.3 and 14.2.1, and
the correction of the UNS numbers for P9 and P91.

RE: P9 / P91 in ASME BPV

hi metengr, not sure if Im getting where you're at. The issue I found was that there's no consistency in the UNS designation for A/SA 335 P91. Im not comparing it with other P91 product form specs.
let me put it simple;
- Say you were to purchase P91 pipe for a Code application. Would you specify K91560 (designation as per II-A) or K90901 (designation as per II-D)?
- The same holds for P9 tube per A/SA-335. If you're going to order this, would specify SA-335 P9 UNS S504000 as per II-A (2017 edt.), or SA-335 P9 UNS K90941 as per II-D (line 3 of the 2017 edt of table 1A, page 46)?

RE: P9 / P91 in ASME BPV

XL83NL, thanks for the follow-up. The material should be ordered to the latest edition of the SA specification. Section II should be notified of the discrepancy in Part D and this may be errata.

RE: P9 / P91 in ASME BPV

Thanks metengr, I'll do so.

RE: P9 / P91 in ASME BPV

One question whcih the Code committee probably cant or wont answer; why is the UNS for A/SA-335 P9 pipe called out as S50400 (indicating stainless), but for other product forms in grade 9 material, like A/SA-182 F9, A/SA-234 WP9 or A/SA-213 T9 called out K90941?

PS; whats the emailaddress where I can send the Code revision request to?

RE: P9 / P91 in ASME BPV

Colleen O'Brien, she is the BPV II Secretary.


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close