Re-Rate, Alteration, Applicable Rules 1

[skasliwal]

Guys,

I have referred a lot of literature on the issue but my problem remains to be unsolved.

I am rerating a few exchangers built back in 1955 to a higher shell and tube side design pressure. To my understanding I can use the code effective at that time along with the old stess values for this purpose. I have no record of what the caclulations were based on back in 1955.
so my question(s) is can i use the 98' Edition of the code ?? Does that mean that the tubesheet can be designed per TEMA (and not UHX)?? How about on the flanges, can we disregard the pass partition rib area, J factor and all the other good stuff that has recently became mandatory ?

Thanks in advance.
Skasliwal

 

[metengr]

skasliwal;
A rerate of this type is considered an “alteration” of the pressure retaining item. Since you did not state where the heat exchangers are located, there could be several options – use the National Board Inspection Code rules for alterations, or follow the Jurisdiction requirements, or if insured or self-insured you need to get a National Board commissioned Inspector involved with your alteration. If you are not using the National Board Inspection Code (NBIC), I would strongly recommend (it is an ANSI international standard) you obtain a copy for this project. The original code of construction as referenced in the NBIC would be used for design calculations to rerate the heat exchanger - original does NOT mean year and edition of the Code the item was built under only the code of construction (ASME B&PV Code or other, so the 1998 Edition of ASME B&PV Code can be used).

If you are required by the Regulatory body or Jurisdiction to follow the NBIC rules for alterations, the heat exchanger will need to be subjected to hydrostatic testing, Inspector review of the design calcs and the necessary NBIC form will need to be submitted to the Jurisdiction or Regulatory body.

 

[Montemayor]

skasliwal:

In 1955 I was still a Junior in High School, so I can’t be blamed for anything wrong with the subject heat exchanger. Levity aside, it has been my policy to re-rate pressure vessels under the strict understanding that the product vessel will be operating under existing, present laws and regulations and as such the vessel should be checked, modified (or re-built) in accordance with present and prevailing codes and regulations. It should not matter if the vessel is 5 years old or 50 years old; the existing present day rules and regulations are meant to protect people today – not yesterday. In the same light, the codes and regulations of yesterday were meant to protect people then – not today.

I presume this exchanger is within the USA and its codes.

I would be very interested if metengr could add some valued comments on the above. As usual, he has made some specific and detailed advisements that add value to this thread. Kudos go to him. Perhaps I am too much of a hardliner and haven’t interpreted the codes well.

 

[skasliwal]

Montemayor:

So you were in junior high school in 1955, so was my dad. Guess I couldn’t be blamed either.
Anyways, I do agree with you, that the equipment is being re-rated in the present time, so the present code must be applicable. But the thing is, since its a pre 1968 exchanger, I have to use the Old stress values. The tubesheet design comes out OK per TEMA but fails when designed per UHX. The question that I really want the answer to is whether it is OK to design the tubesheet per TEMA, since UHX had became mandatory just recently. looks like from metengr's post that its OK to use TEMA (Since UHX was not mandatory in 1998 edition of ASME sec VIII, Div. 1)

Also, I believe if it were an alteration, we’d require a R stamp nameplate and the inspector does not need to certify the designs. Any comments ???

Skasliwal

 

[metengr]

skasliwal;
What you are proposing is indeed an alteration, and the Jurisdiction or Regulatory body needs to approve the design calculations, per the NBIC requirements for an alteration (see RC-3022). You might be able to make a case for using TEMA versus UHX, but it will be up to the Jurisdiction or Regulatory agency.

Regarding allowable stress values, you cannot use higher allowable stress values based on a reduction in allowable stress from 4 to 3.5 in the later edition of the code of construction, if the item was constructed prior to the 1968 edition of the code of construction, as you stated.