Replacement of Heat Exchanger channel to higher grade material - Repair/Alteration/New Equipment 1

[inammanj123]

Hi,

I have a BEU type exchanger on old asme sec div.1 edition. job is to upgrade exchanger by replace channel bonnet to new 1.25Cr material. This is done because service is hydrogen temperature is high, so chance of HTHA is there. Shell side, tubesheet and tube will remain same. Client is ARAMCO. In this regard i have following question:

1- keeping in view that process conditions will be same, calculations need to be performed as per latest asme edition, so to make sure girth flange dimensions, nozzle project mates with existing dimensions, will it be alteration job or repairing job and will channel have r-stamp or simply U-part?

2- If client ask to check tubesheet and tube in accordance with latest TEMA AND API 660, what are few major condition i need to look for to propose a change in tube sheet.

3- For new channel design, I think i will limit MAWP and hydro-test pressure?

Thx

 

[Dhurjati Sen]

How old is the exchanger?

Did HTHA really take place, or was it always presumed that it would take place some day?

Ask ARAMCO what stamp would satisfy them and then go for it.

If such recommendations are being really made, then God save ARAMCO !

DHURJATI SEN
Kolkata, India

 

[Christine74]

1) Generally replacing a channel on a heat exchanger would require an NBIC Alteration (R-2), because the vendor is likely to change the head/girth flange/nozzle thicknesses. However, it might be possible for a replacement channel with new metallurgy to be considered to be an NBIC Repair, provided that the component thicknesses all match the existing design AND the materials all have an allowable stress that is at least as high as that of the original component. Confirm with your AI but in general if you have to run code calculations for modifying the equipment it will require an R-2 Report of Alteration.

The new channel could be documented on a R-1/R-2 form, but most likely it would be documented on a U-2 Manufacturer's Partial Data Report form. If the existing heat exchanger is sent to the R stamp holder's facility, they could prepare and sign both the R-2 and the U-2. Otherwise the field contractor who installs the new channel onto the existing shell should take responsibility for signing the R-2. Again, check with your AI.

2) I don't know when this exchanger was built but the tubesheet may have originally been designed per ASME UHX rules. If so there's a small chance that it may not meet TEMA rules.

API 660 does not have any rules for tubesheet calculations as far as I know.

3) If the new channel MAWP is higher than it was in the original design, the existing nameplate won't have the correct information on it, which could cause issues in the field and could potentially trigger a re-rate. Again this is something you would need to discuss with your AI.


-Christine