Different Grade between Pipe/Flange/Elbow

[if7005]

Hi all pipeliner,
Can we use fitting A234 for Pipe X42 ( use B31.8code ) with same schedule 12.7 mm ?
As we know , design factor(F) shall be considered in Thickness calculation of B31.8 for pipe.
But no rules to calculate Fitting thickness with including design factor in this code.

 

[BigInch]

No. A234 is not equal to X42, so a different wall thickness must be used for the fitting. For equal design pressures in each, fitting walls must equal at least that of the pipe wall and, if it is the same wall thickness, then it must also be certified to at least the same yield strength.


Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[if7005]

BigInch,
I agree with u, since this is common rule to equal grade and thickness.

But if we see 31.8 : t=PD/(2FES), which include design factor F=0.4 in this case, only used for PIPE not for other component (fitting, flange,etc).

Why shall be same in grade and thickness ?

Regards,

 

[BigInch]

The design pressure is?

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[Zapster]

So this begs the question of what A234 is equivalent to in B31.8. I know that if7005 asked specifically about B31.8; however, some B31.3 data makes me wonder. I know that SMYS are NOT interchangeable between the two codes; however, B31.3 list the tensile strength for both at 60ksi, the yield strength for both at 42ksi, and SMYS at 20ksi for both A234 and API 5L X42.

If I look at CFR 192 it states that "Each steel butt-welding fitting must have pressure and temperature ratings based on stresses for pipe of the same or equivalent material."

If one goes off the mil certs, then could they use A234 fittings for X42 pipe?? If they can't use the mil certs, them I am back asking what standard can you use to determine what welded fittings go with API 5L pipe?

I took a look at ASME Section 2, sub D and did not see API 5L (I am not surprised). So if you cannot use mil certs, then what published data is appropriate to make the determination that would have both API 5LX42 and ASTM A234?

 

[BigInch]

You just have to look at the code.
Allowed yield stress is by grade ordered and certified.
B31.8 Appendix D - Specified minimum yield strength for steel pipe commonly used in piping systems.
API 5L A25 is 25ksi
API 5L A is 30ksi
API 5L B is 35ksi
API 5L X42 is 42ksi
The pipe was apparently certified to one of the above, and the fittings are certified one of the ASTM A234 grade strengths, but so far the grade of A234 has not been given; B is most common.

In any case, with equal wall thicknesses, and no change in design pressure, in this case the design pressure could not be higher than that allowed for the lower grade material.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[SJones]

Just follow what it says in B31.8 - look at MSS SP-75 or ASME B16.9. There it defines how to pressure rate fittings. So far, we have no design pressure or grade of fitting defined, so how long is a piece of string?

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[BigInch]

Or diameter(s)

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[if7005]

Thanks for all response,
Here I just ordered to verified existing fabricated spool which consist of pipe API-X42 connected to A105(Flange #300) and A234-WPB(fitting).

This spool will be operated at following condition :
Design code: B31.8
Design Pressure/Temperature = 50 bar / 66 C
OD : 16 inch
Thickness : all 12.7 mm
Location design factor : 0.3 (local government regulation)=>applied only for pipe

Will this spool be within the allowed stress and accepted by code?

According to 31.8 :
Thickness requirement is 12.7 mm with 42000 psi of yield-s.
As we know it specify only for pipe ( no rule of b31.8 to calculate fitting thickness or specifiy the fitting material, so the guy selected A234-WPB and A105 with same thickness ).

 

[BigInch]

NOOOOOOOOOOOOOOOOOO!

BTW that's absolutely no.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[BigInch]

BTW it would seem that you are in the temperature derating range too.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso

 

[if7005]

BigInch,
Thanks for advice, but please give your reason base on code requirement. Really confused to decide.

SJones,
B16.9 say only about thickness, not grade to rate the fittings.

 

[BigInch]

Without intending to be insulting I have to say that you need to get some experience before you get yourself and your company in a heap of trouble. At least read the design code. This type of question defies the most basic engineering logic and IMO would not even have to be addressed directly by a design code, but the code apparently has anticipated your attempt to use it. Basically, if you can't decide what you need to do in this kind of a situation, you do not have enough engineering knowledge or design experience to go any further.

fittings .... shall have pressure and temperature ratings based on stresses for pipe of the same or equivalent material.

I'll let you do the doc search yourself. At least I'll know you read a few words of it.

Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso