Repair of Tubesheet with severe thickness loss

[shaafishaikh]

Hello all,

My question is regarding a shell and tube U-tube heat exchanger designed to ASME Sec VIII Div.1 1992 and TEMA 7th Ed 1988 Class R.

The exchanger's tube sheet is 54 mm thk A105 Carbon Steel cladded with 8 mm SS216L.
The carbon steel is suffering from severe metal loss after coming in contact with concentrated acetic acid. More than 75% thickness has been lost over 20% of the tubesheet area. The rest of the tubesheet is fine. The cladding is okay too.
What options are available for tubesheet repair (other than replacement) from the Code perspective?

Weld build-up of the carbon steel comes to mind, however given the thickness I would like some Code references.
Codes I have been through include API 510 and ASME PCC-2.
There is nothing specific to tubesheets in API 510, and ASME PCC-2 does not give many options either.

Shaafi

 

[metengr]

The other in-service repair code which would apply is the NBIC. Here, Part 3 can be used to provide guidance for weld build-up of a wasted tubesheet using guidance in Figure 3.3.4.3 (a).

 

[chicopee]

With over 50% of the wasted tubesheet thickness, you should first ask the authorized inspector if weld buildup per NBIC recommendation is acceptable and such inspector may also ask for additional NDE.

 

[EdStainless]

I am sorry but I see repair of this as a fools game, one with no winners.
You will be replacing all of the tubes, you will be re-drilling all of the holes, and you will have an old tube sheet.
Get some serious bids on replacement.

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Plymouth Tube

 

[metengr]

Sometimes one does not have the luxury of simply replacing when $$$ are lost per day. Flush path repairs or weld overlays are performed on tubesheets with good success.

 

[shaafishaikh]

Thank you all for your valuable inputs.

EdStainless, while replacement is definitely the ideal scenario, metengr's point is a valid one.
Further, I dont think any tube replacement is necessary. Why is that you feel all tubes will need to be replaced?

Thank you metengr for the reference to the NBIC. I was not aware of this code before. I am still going through it.
Are the repairs only acceptable after consulatation with an authorized inspector?

 

[chicopee]

You should consult with an AI before the repairs.

 

[EdStainless]

Well if you don't replace the tubes you will shorten them by the thickness of the tube sheet.
If you do weld buildup on the tubesheet you will have to remove the tubes, right?

Which face of the tubesheet are we talking about?
After all if it is the back face then you will need to remove the tubesheet to repair it, and once you do that replacing it is easier and faster since the replacement would be on site already.
If it is the front face then with the amount of surface prep required (grinding and/or blasting) you would destroy tube ends, and that is before you start to weld.

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Plymouth Tube

 

[StoneCold]

I have to believe that there is a good second hand un-used heat exchanger out there that could be used to replace this one with much better results.

Regards
Stonecold

 

[Guest102023]

I have to go with EdS on this one.
Of course anything is possible, but recovery of 50% loss is a massive undertaking fraught with technical difficulty.
Probably I would opt for the minimum amount of welding to make it shipshape, and in the meanwhile I would order a replacement.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[shaafishaikh]

Thank you for all your replies.
Currently we are looking to replace the damaged exchanger with a different exchanger from a defunct part of the plant.
Meanwhile we are weighing the options of repair of tubesheet by weld build up, replacement of tubesheet, and replacement of entire tube bundle.
Once the exchanger is out of service we should be able to get a better look at the damage and hopefully I can post pictures as well.

 

[chicopee]

Are you applying for a "R" stamp once repair is completely and HX hydrotested?

 

[Duwe6]

Done this repair before: Cut the tubes loose from the tubesheet. Have a new tubesheet made [can be machined ahead of the shutdown]. Install the existing tubes into the new tubesheet. Yes, you will loose about 6-inches of tube length = bundle length loss; you will not be able to measure the slight loss in heat transfer efficiency.

Even if your Inspector is comfortable with that huge weld buildup on a tubesheet, the above method is quicker, thus cheaper - less lost production time. Repair costs are similar on both methods.