Was A 335 P 11 material allowable stress In 1992 ASME/ANSI B 31.1 & 1994 ASME/ASNI B 31.3 higher from as it is today in B 31.1 & B 31.3 in creep range (ie above 750 F) ?

I don't think that such a situation is possible.
If it is true, for any piping designed with the relevant B 31.3 code in 1994, will be inadequate in thickness, if recalculated with today's edition of B 31.3, if required for to recertify for any modification to be made today ?

Library data as reprinted below show that allowable stress has been raised, not lowered with time from 1994 in ASME B 31.3 in creep range.

1995,1998,2001 B 31.1 Allowable stress

700 750 800 850 900 950 1000 F
15 14.8 14.4 14 13.6 9.3 6.3 ksi

1999,2002 B 31.3 Allowable stress

700 750 800 850 900 950 1000 F
15.6 15.2 15 14.5 12.8 9.3 6.3 ksi

1994 B 31.3 Allowable stress
(as noted from Page 8-173 of Intl 1987 9th Ed
of Marks Handbook of Mech Engineers)

600 800 1000 F
16.8 12.8 5.8 ksi (B31.3:1994)
16.7 15 6.3 ksi (B31.3:2002)

Can any veteran forum member remember the reason for any such changes in allowable stress of A 335 P 11 ?

regards,

sam

Hello Sam,

You understand the methodology that B31 Codes use to determine the maximum allowable stress limits that are found in Appendix "A" (these methodologies are described in B31.3, paragraph 302.3). ASTM-335, P11 was an anomaly. The original allowable stresses for this material were determined using the normal procedure. However, experience from operating systems through the years demonstrated that there was a problem with creep-fatigue interaction with this material, especially at branch connections. The Committee's response to this new information was to lower the allowable stresses for ASTM A-335, P11 to the magnitudes that are now in the Codes.

When we reexamine (using NDE and new analyses) existing operating systems for their "fitness for continued service" we look again (with a little extra rigor) at the branch connections and we use the current allowable stresses.

Regards, John.

A335 P11 Allowable stress in tension
700 750 800 850 900 950 1000 F
15.6 15.2 15 14.5 12.8 9.3 6.3 ksi (latest B 31.3)
15.6 15.2 15 14.5 12.8 11 7.8 ksi (1990 B31.3)
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To John Breen,

Thank You, Sir for your reply.

From your response, it is understood that the allowable stress for A 335 P 11 had been lowered in creep range & for any recertification of existing operating systems designed with earlier higher allowable stress, the practise is to use the current allowable stress & extra care at branch connection "fitness checking for continued service".

With the above approach, stress analysis may qualify for new analyses, if we had kept some factor of safety hidden in our earlier designed system. But, what about thickness calculation as per B 31.3 Part-2 clause 304.1.1 eq (2) & 3 (a)?
Will it be fulfilled with lowered latest allowable stress ?

regards,

sam

Hello Sam,

Yes, to comply with the Code we must use the current allowable stress limit (Sh) for the pressure equations. While fatigue might not be a deciding issue in steady state pressure design, it is certainly working in concert with other loadings. The Code considers all the primary and secondary stresses when determining the appropriate magnitude for the various allowable stresses and stress ranges.

Regards, John.

A335 P11 Allowable stress in tension
700 750 800 850 900 950 1000 F
15.6 15.2 15 14.5 12.8 9.3 6.3 ksi (2002 EdB 31.3)
15.6 15.2 15 14.5 12.8 11 7.8 ksi (1990 B31.3)
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For the above example of welded pipes (i.e. not seamless) P11 material application in 1000F (above 950 F, in the creep range), if we want to check straight pipe thickness for internal pressure as per para 304.1.2 of 2004 Ed of ASME B 31.3, will we require to multiply SE with W - weld joint strength reduction factor = 0.9545 at 1000 F (linearly interpllated between 950F to 1500 F with values at 1.0 & 0.5 )& require even a higher thickness than that was required in B 31.3 :2002 edition ?

Will it not create complication in modification of any existing piping with new piping in the creep range, requiring higher thickness due to lowering of the effective hot allowable stress SEW for thickness calculation, pressure rating determination as per para 302.2.2 & sustained allowable stress comparison as per para 302.3.5 c ?

For seamless pipes, at longitudinal welds, sustained allowable stress comparison as per para 302.3.5 c will not require consideration of W - Is it right ?

What could be the alternatives available for welded pipes - to ask for better W values from piping vendors with typical creep testing of welded joints or use API-570 as post construction code for any repair or go for seamless pipes only in creep range?

regards,

sam