A335-P11 - allowable stress -1960s ? 2

MJCronin;
I would suggest you contact MPC ( because they have a comprehensive database on Cr-Mo materials. MPC has access to a number of sister organizations like PVRC and the WRC that could locate this specific information (this is not a commercial plug).

I do remember a paper that was published in the 1980's (shortly after the Mohave steam line failure) that mentioned the revision (lowering) to the ASME B&PV code allowable stress values for 1.25% Cr - 1/2% Mo alloy steel -and reasons for this revision.

If I can find this paper, I will provide the date and author.

I also have the report mentioned by metengr. I’ll bet he finds his before I can find mine.

Some Info on P11
Look at the bottom of the page.

BR#1586

There was a brief, well written technical article by Brown & Root Power titled, "P11 Piping Allowable design stress revisited". It was published by Mr Joe Gephart in a magazine called The Power Chronicle. I don't have an actual date because I have a copy of only the article that was given to me. However reference was made to a recent code revision in 1991 for P11.

Anyway, to summarize;

A chart was provided with the article that shows the allowable stress reductions starting from 1951 to 1955 to 1967 and to 1991 within the elevated temperature ranges of 950 deg F to 1050 deg F. A major change in allowable stresses was noted in 1967 - the allowable stresses were reduced by up to 25% in elevated temperature ranges.

Another 15% reduction in allowable stresses was reported in 1991 for P11.

Apparently creep crack propagation tests were conducted to show the affects of changes in allowable stress. The information provided in the article compared creep crack growth rates at 1005 deg F using the 1991 (recent code revision at that time) allowable stress value to the allowable stress values in 1967 and 1955. The results were dramatic;

- using a 1991 allowable stress at 1005 deg F base line crack growth rate established
- using a 1967 allowable stress, at 1005 deg F a 6% increase in crack growth rate was observed

- using a 1955 allowable stress, at 1005 deg F a 60% increase in crack growth rate was established.

The article posted by metengr may be available at:


I seen mention of an ASTM Standard WK 658 for AE testing of steam lines that is supposed to be out anytime.

Sure glad we only had 650 psig @ 750?F steam. We were also fortunate in the man that oversaw the design, construction, and running the Powerhouse didn't skimp on materials.

Many thanks to "unclesyd" and "metengr" for thier informative posts...

The website references are very helpful....

I also found allowable stresses in an old 1960's vintage(?) book by "Brownell and Young".

The allowable stress levels matched exactly with those stated in the B&W plants Services Buletin PSB-1

After reading up on this topic, I am beginning to wonder,..... Is there anyone out there still using P11/T11 materials ? Havent the more fatigue resistant, higher chrome-molly materials become the standard ?

MJCronin

P11 is still in use albeit far less than in the past. The newer alloys such as P91 are all the rage, but my own personal opinion is that the weld/fab difficulties associated with this alloy may its application problematic especially if the the fab shop is selected soley on price!

P91 has fantastic properties but its very difficult to achieve these properties in welded construction.

Regards,
XHPIPE

ANSI A335-P1 is a good material within (as all materials) its limitations. The Committee applied "lessons learned" when creep-fatigue interaction failures were reported (especially at branch connections). The current limitations on 335-P11 as specified in the B31 Pressure Piping Appendices "A" are appropriate.

I would like to say that A335-P1(C-0.5Mo) is no longer preferred/ used. Most users have barred carbon-molybdenum steels for all new constructions.

Thank you to all who have contributed

MJC