Minimum thickness on a 30 year old pressure vessel

[MechDesign105]

Hi,

We own about 900 pressure vessels dating to about 1980. How do I calculate the minimum thickness required for these pressure vessels? I am under the impression that I need to use the ASME B&PV but I am curious as to what edition I need to use. It seems to me using the last edition (2010) is not correct since this original pressure vessel was not constructed following the 2010 edition but the 1981 or prior editions.

Which edition should I use? Does the NBIC prescribe minimum thickness calculations while inspecting (after Xray or ultrasounds)?

Thanks!!!

 

[MechDesign105]

Hey Guys!

I've found a thread that pretty much answers my question.

It states the following :

INTERPRETATION 95-19
Subject: RC-1000 General Requirements
1995 Edition
Question: When the NBIC references "the original code of construction," is it
required to use the edition and addenda of that code as used for
construction?
Reply: No. The term "original code of construction" refers to the document itself,
not the edition/addenda of the document. Repairs and alterations may be
performed to the edition/addenda used for the original construction or a
later edition/addenda most applicable to the work.

When it says : «most applicable to the work», what exactly does it mean? Does anyone have an example of a situation where the old code NEEDS to be used?

Also, do the new allowable stress values need to be used even though the original code uses older values?

Thanks!

 

[stanweld]

The NBIC controls repairs and alteration to existing vessels. Your vessels would have been designed to the 4:1 safety factor at that time. the vessels could be rerated using the 3.5:1 Safety factors of today if youi so choose. You will need to verify remaining thickness and should use API 510 as a guide for inspections for fitness for service, repair, derating or rerating.

 

[Duwe6]

API-510 gives you the proper calculations, including estimating End-of-Useful-Life, and the scheduling of the mandatroy inspections. You probably should hire a 510-certified Inspector, or put in the training time to become one yourself. 900 vessels is more than one Inspector can keep up with, most likely.

Also see: thread 794-248585 on rerating using the 'New" post-1999 allowable stresses. Add Indiana to the "No-No" list, along with California, etc.

 

[MechDesign105]

The 3.5:1 safety factor of today is in the Division I of the B&PV right?

As I understood it the Division II is more application based than Division I. Are the safety factors the same?

Should I use API even if my pressure vessels are not petroleum related (solely dry air)?

 

[stanweld]

The 3.5:1 safety factor is in today's Section VIII, Div. 1.

Section VIII Div II is primarily used for heavy wall pressure vessels due to its lower safety factors. You may not upgrade from Div. 1 to Div. II.

Your Jurisdiction will provide whether API 510 can be used. If the Jurisdiction is a Code State which required the vessels to be registered with the National Board, use NBIC for rerating, if that is what you intend. Use the original Code design allowables for determining present min wall requirements at pressure/temperature.

 

[MechDesign105]

Hey stanweld,

Thanks for your reply. There has already been a calculation done using the Section VIII Div I of 2010, which from what was said in this thread has smaller SF than the one from 1980. The minimum wall thickness calculated was bigger thant the one measured, which is not good!

However, the funny thing about it is that the original design min thickness is also smaller than the thickness calculated!

I have had so much trouble talking to my Jurisdiction (i'm in Quebec, Canada). However I assume that this finding means the original code used was NOT ASME. However there is a Jurisdiction ID number on the pressure vessel (here it's a CRN #) and that means the original design was accepted by the jurisdiction. Therefore they have all the design information and calculations on-hand.

I'm currently trying to contact them again.

 

[stanweld]

While unaware of the Canadian Standards, British PV Standards and some oher European PV Standards at that time had higher design allowables than ASME VIII, Div.1. That was one of the primary reasons for the Div. 1 changes.

 

[MechDesign105]

Well if that is the case they need to be removed from service. Our law states ASME and NBIC as requirements but I think that our Jurisdiction can accept pressure vessels made with other standards if they are judged equivalent. This particular vessel is a Voest-Alpine from Germany.

I have a further question : is the thickness written on the plate found on the pressure vessel the thickness with the corrosion allowance or the minimum thickness calculated without the corrosion allowance.

 

[rustbuster]

The name plate should indicate the nominal thickness, subtract the corrosion allowance and you will have a value to use.

The calculated minumum thickness should be from the original code of construction. As others have said, API-510,NBIC and CSA B51 should be referenced.

 

[stanweld]

To my knowledge, the Div. 1 nameplate did not require stamping the thickness there on in 1980; at least, it has not as of the 1998 Edition.

The vessel may well have been designed and constructed to the AD Merkblatter Code. You should have some evidence as to which Code the vessel(s) were made.

 

[fegenbush]

The Division 1 nameplates *still* do not require the stamping of the thicknesses on the nameplate as of the 2010 edition. I would use API 510 or API 579 (ASME FFS-1).

 

[Millar]

Canadian Standards adopt ASME for design and construction of pressure vessels as a general rule. While it is possible for the jurisdiction to have allowed design and construction to a different standard, in my experience these are special one of a kind cases (mind you I have not had any experience in Quebec). Is there a U stamped on the upper left side of the nameplate? If so, then this vessel is still ASME code even though it is fabricated in Germany.

As far as fitness for service, you need to check with the jurisdiction to ensure that they will accept what you are doing. Canadian provinces retain jurisdiction over pressure vessels. The Quebec Boiler and Pressure Vessel Regulations will apply, then CSA standard B51 and then you may apply good engineering practice like using API 579 (provided the jurisdiction accepts your approach).