API 5L Gr. X70 as pressure vessel shell

[GonzaloMartinez]

Hello everyone, I know that this issue has been discussed before but I need further help please. The thing is that it came to me a 36" diameter pressure vessel whose shell is made of a API 5L Gr. X70 welded pipe. I want to know if this material can be recertified as a material accepted by the code under what it is stated in paragraph UG-10 a) 1), the owner of the equipment has provided the manufacturer's documentation that certifies the origin of the pipe.

Thank you.

 

[weldstan]

It may be possible depending on chemistry, mechanical properties, pressure testing and NDE of weld seam. I would suggest that the mill do the recertification, if it can. One problem may be the min wall requirements for the new certified ASME material, assuming the vessel was designed to ASME VIII, Div. 1.

 

[jte]

Gonzalo-

In general it would be good for you to state specifically which code you are working with. Based on your UG-10 reference I will presume that you are working to ASME VIII Div. 1.

Sounds as though the vessel has already been fabricated. It's a bit late to think about an ASME code stamp.

If the vessel was not yet out of the fabrication shop, you could compare the MTR to see whether the material meets some SA grade.

My understanding of API 5L is that it is quite a bit looser than ASME vessel materials. Just look at the huge range of tensile stresses:
Specified minimum yield could be as low as 25,400 psi or as high as 120,400 psi while specified minimum tensile values vary from 45,000 psi to 132,700 psi.

Needless to say, the chemistry and steelmaking practice for 5L has a wide variation.

Most of the steels used for Section VIII work have a yield : tensile ratio on the order of 70%. This allows for a bit of plastic action before hitting yield, effectively giving some forgiveness of local strain issues. On the other hand, your 5L X70 has a yield of 70.3 ksi with an ultimate of 82.7 ksi for a yield : tensile ratio of 85%. This is a substantial reduction.

The vessel is probably usable, but be careful of details which may be in the 1.5*S or 3*S range. But you probably cannot make it Section VIII compliant and put a U stamp on it.

 

[GonzaloMartinez]

Thank you weldstan and jte for your help. Sorry jte, I was in a hurry and I missed that important piece of information... yes, I am working with ASME BPVC Section VIII, Division 1. You are rigth, the pressure vessel was fabricated few years ago, it doesn't have any ASME stamp. The actual owner has very little documentation of it and wants to do a verification of the equipment in order to determine if it is safe or not to use it. We suggested to analyze if it meets ASME VII Div. 1 but early in the job we got to this material problem.

 

[weldstan]

You need to do a stress analysis to determine the applied stress versus yield strength. It is noted that X70 is often thermo-mechanically conditioned to produce the tensile values and the strength will be more temperature sensitive than SA-516 and higher strength low carbon alloy steel materials permitted under ASME VIII. Use B31.3 as a guide for max T.

 

[metengr]

You are rigth, the pressure vessel was fabricated few years ago, it doesn't have any ASME stamp. The actual owner has very little documentation of it and wants to do a verification of the equipment in order to determine if it is safe or not to use it. We suggested to analyze if it meets ASME VII Div. 1 but early in the job we got to this material problem.

You will not be able to stamp the vessel after the fact - meaning post fabrication. Your option is to petition for a state special (if applicable) or if there is no regulatory body, leave as is, unstamped or look at API 510. You cannot go back and stamp a vessel using the certification mark after it has been fabricated.