Allowable stress for API 5L materials in ASME VIII calculations. 5

[gbratis]

Hi folks
You noted once that I shouldn't use API 5L piping for an ASME VIII div.1 vessel. Even though I dont seem to understand why, since you can use an A 106 Gr.B PIPE!, now I'm in the position of no turning back where I've used an API 5L X 65 pipe to lower the calculated thickness of the vessel. The crucial thing is to obtain the allowable stress value for this material.There is no ASME II part D material index for this pipe so I'll have to estimate one.Since all the allowable stresses of the ASME VIII code utilize the 28,5 % of the tensile strength of the material, is it permissible to do the same for the non ASME classified material? Is it ok to use 75.000 psi (API 5L X65 tensile strength) x 0.285 = 21375 psi as the allowable strength? Your mature reply will be highly appreciated

 

[metengr]

gbratis;
Is this pipe for new construction of a pressure vessel or to repair/alter an existing pressure vessel??

 

[deanc]

Suggest you get a MTR for this stick of pipe. API 5L covers about 10~15 different types,some may be OK,some not.

Sometimes this pipe is dual marked such as API 5L/SA-106B ASME or API 5L/SA-53EB ASME,it could be a type F,or not marked for ASME at all. The Grade and Type of a stick of API pipe may be ASME acceptable and maybe not.

You must always be very careful. Read the "Forward" of any Code section for guidence. Cross reference the material specs. in Sec II A. Do your homework----if in doubt do not use it.

 

[jte]

I guess I'm a bit confused:

...I've used an API 5L X 65 pipe to lower the calculated thickness of the vessel.

followed by

The crucial thing is to obtain the allowable stress value for this material.There is no ASME II part D material index for this pipe so I'll have to estimate one.

seems to be contradictory. How can you already have lowered the calculated thickness of the vessel if you haven't yet figured out the allowable tensile stress?

I presume you are at least talking about a vessel whose design temperature is ambient and that the "or 2/3 yield" part of the allowable stress basis doesn't apply and that compressive stresses do not govern. Further, you have no intention to code stamp this vessel - you are only using ASME VIII as a guideline. If so, then using the specified minimum UTS divided by 3.5 is not an unreasonable approach to developing a tensile design stress. I'd stay away from using MTR values for a couple of reasons: Your calc's may be used later by someone else who presumes that the MTR value for your vessel is equal to or lower than the MTR UTS for their vessel. Second, how do you deal with it when the time comes to repair the vessel and the original material isn't available. The savings for going with MTR values instead of specified minimum values can't be that great.

jt

 

[deanc]

jte: Good point!

 

[VeryPicky]

It is not advisable to use material that not listed in section II of ASME BPV Code. If you insist to do that, approach it with extreme caution. Review UG-10(a) that seems to be the most applicable to your case and ensure you can use the material on the vessel at all. If it can be used it needs to be recertified.
All this was written under assumption that you are building an ASME VIII vessel for a regulated jurisdiction. If there is a local variance approved for API material, just go for it.

Putting Human Factor Back in Engineering

 

[gbratis]

Thanks everybody,
Jte to clarify things up I'm adding some remarks on your original post :
I presume you are at least talking about a vessel whose design temperature is ambient (No) and that the "or 2/3 yield" part of the allowable stress basis doesn't apply (We are not performing test at known condition so as to compare information with similar materials) and that compressive stresses do not govern ( I cant understand the meaning of the term "compressive stresses"). Further, you have no intention to code stamp this vessel (No) - you are only using ASME VIII as a guideline (Correct). If so, then using the specified minimum UTS divided by 3.5 is not an unreasonable approach to developing a tensile (no tensile-max allowable) design stress. I'd stay away from using MTR (Sorry I dont know what MTR stands for) values for a couple of reasons: Your calc's may be used later by someone else who presumes that the MTR value for your vessel is equal to or lower than the MTR UTS for their vessel. Second, how do you deal with it when the time comes to repair the vessel and the original material isn't available (It is a circumstance, unlikely to happen). The savings for going with MTR values instead of specified minimum values can't be that great.

As for Very Picky I believe that the ASME VIII vessel is not intended for o regulated juristiction.Even though I dont seem to understand the term "local variance" I believe that I can proceed with my estimation. If local variance has to do with the third party inspector sanction of my approch then I assume that everything is ok. I'm I right?

 

[stanweld]

MTR is the Materials Test Report defining the actual tensile properties obtained from coupons taken from the heat of material per the API 5L Specification. In terms of using ASME VIII, Div. 1 as a guide for design, the appropriate tensile strength to use is the Specified Minimum Tensile Strength per API 5LX-65, not the value shown on the MTR.

 

[jte]

I presume you are at least talking about a vessel whose design temperature is ambient (No)

If your design temperature is not ambient - which is the temperature at which either the MTR (see above post by Stan) is obtained or the SMUTS (specified minimum ultimate tensile stress) or SMYS (… yield stress) is specified - then how do you plan to develop allowable stresses which correspond to your design temperature?

and that the "or 2/3 yield" part of the allowable stress basis doesn't apply (We are not performing test at known condition so as to compare information with similar materials)

Ummm… see above comments… You better be confident here. Allowable stresses of commonly used ASME SA carbon steels are governed by the "or 2/3 yield" criteria at temperatures as low as 600 deg F.

and that compressive stresses do not govern ( I cant understand the meaning of the term "compressive stresses").

I really hope this is a language / translation issue and not an engineering knowledge issue. By compressive stress I mean a stress which tends to force the material together. If a tensile (pulling apart) stress has a positive sign then a compressive stress is negative.

Further, you have no intention to code stamp this vessel (No) - you are only using ASME VIII as a guideline (Correct).

Good.

If so, then using the specified minimum UTS divided by 3.5 is not an unreasonable approach to developing a tensile (no tensile-max allowable) design stress.

If you don't recognise that there are several "max allowable" stresses in any ASME VIII vessel then I'd question your ability to safely design one. See second quote above for one example.

I'd stay away from using MTR (Sorry I dont know what MTR stands for)

See Stan's explaination in the above post.

Second, how do you deal with it when the time comes to repair the vessel and the original material isn't available (It is a circumstance, unlikely to happen).

By original material, I mean the exact twin of the material from which the vessel was fabricated - same mill run / heat. Unless this vessel will be thrown out when it wears out it will need some repair someday. That repair may use another API 5L pipe or weld build up which has lower MTR values thus invalidating your design if you based your design on your current MTR values instead of specified minimum values. Only by then the paperwork will be lost and nobody will know that the repair does not meet the original design. (I'm such a pessimist! Can't claim to be "born in the trenches" but I've been in 'em.)

As for Very Picky I believe that the ASME VIII vessel is not intended for o regulated juristiction.Even though I dont seem to understand the term "local variance" I believe that I can proceed with my estimation. If local variance has to do with the third party inspector sanction of my approch then I assume that everything is ok. I'm I right?

What Mr. (or Ms.?) Picky is referring to is that you need to check with the local authorities to see what they require for pressure vessel design and construction. In the USA some states require that vessels be built to ASME VIII or another "equivalent" code (to allow for foreign code use) while some states have no requirements and leave it to the individual owner/user/designer/fabricator to decide how to design and build a vessel. Basically, Mr. Picky is pointing out that you'd better check your approach with the folks who can put you out of business or in jail before you proceed.

jt

 

[GenB]

very hard topic,
i would lower 25% of that of the a106/a53 Smls or a53E pipe
as as the api pipe form of construction,
why: api pipe locks an NDE test and that makes it unfit for ASME Construction.
it can not be used in ASME Construction and be careful of asking around:
The National Bd or the Jurisdiction can recall your vessel...
it is that serious...
genb

 

[VeryPicky]

gbratis
variance is a deviation from a code granted by local authority as a blanket or for a specific purpose. It can be issued for any code requirement: insppection, test, design, material etc.
In regions regulated by jurisdictions those jurisdictions specify design, fabrication and testing codes-criteria and also, specify any deviations from them - hence "variance".

Putting Human Factor Back in Engineering

 

[GenB]

caution:
the use of non ASME materials is a Code violation,
and can be NB investigatd depending on the seriousness of he case,
The AI who inspected and signed will be in a lot of trouble too...
The jurisdiction can asses the problem and give-in in an existing vessel/job
but they can penalize you as well.
genb

 

[jte]

Folks-

Keep in mind that gbratis has stated that the vessel will not be code stamped. This vessel will most likely not be installed in the USA and if it is it will be in a non-code state. So... no AI involvement required and no NB issues.

jt

 

[stanweld]

gbratis,
In terms of why ASME VIII, Div. 1 permits A-106 but not X-65, the following is provided. A-106 B has a long term history of use within the allowable design parameters of the Code; the elevated temperature mechanical properties have been well defined. X-65 is often thermo-mechanically processed and highly micro-alloyed to provide its higher minimum room temperature tensile properties. These processing variations can greatly affect elevated temperature strength of the X-65 relative to that of A-106.