PWHT of S&T HX Shell-to-Tubesheet Flange 4

[KernOily]

Hi guys. S&T exchanger, type BEM, in shop to repair the flange face on the shell flange (shell-to-tubesheet) for corrosion damage.

Shell: SA106B shell 24" sch 100 pipe x 324" long, 1.531" wall
Shell flange: SA105 shell flange 24" class 900.

The flange face is being repaired by weld overlay of CRA then machining back to spec. The WPS position of the weld repair to the flange face is flat, which means they will cut the flange off the shell, do the repair, then weld the flange back on to the shell.

Do I need to be concerned about the PWHT of the shell-to-flange weld pulling the flange face out of plumb? That would be Very Bad if it happened. I've seen vessel shell nozzles get pulled out of plumb, but those weren't as critical as this. The tubesheet gasket won't seat if that happens.

Thanks guys. Pete

 

[Dhurjati Sen]

Not as per ASME Sec VIII Div B.

But could be a service requirement, like sour service, etc.

DHURJATI SEN
Kolkata, India

 

[Christine74]

First I don't understand why a BEM exchanger would have a shell-to-tubesheet flange. This would create a gasketed joint between the tubesheet and the shell flange that you didn't have access to. Normally the tubesheets are just welded directly to the shell on BEM exchangers as shown in the figure below:

https://www.thermopedia.com/cn/content/1121/

Also I'm not sure I understand the question. Are you saying that the shell side of the exchanger was originally Post Weld Heat Treated?

PWHT or not, cutting off and rewelding the shell flange in place could certainly cause the flange to move out of plane, cause the shell to oval, cause the overall length of the shell to shrink, etc.


-Christine

 

[Krausen]

Yes I believe you do need to worry about this if PWHT is required on the shellside due to service environment. This is the reason I will typically specify a 3/16”-thk future machining allowance on all PWHT girth flange gasket surfaces. Allows you to simply machine down the surface in the future if needed without dealing with any WMBU (weld metal buildup) repair & required PWHT.

 

[r6155]

Try to avoid any welding. Check required flange thickness and machine accordingly.

Regards

 

[SnTMan]

You know, Christine74 is right about a shell flange not jiving with a BEM exchanger. This type would normally be a fixed tubesheet, non-removable bundle exchanger with both tubesheets welded to the shell. Tubesheets with extended rim for a bolting flange to attach the channels. Fig UHX 13.1 does show a configuration with tubesheets gasketed to the shell but that is very unusual. Some confusion here.

Ordinary practice in shell & tube exchanger fabrication is to finish machine channel flanges after welding and PWHT, if any. Finish machine of shell flanges after welding and PWHT, if any, is pretty uncommon as portable equipment is usually required. I can't prove the following statement, but it seems that Apx 2 flange designs with "ordinary" proportions provide enough flexibility in the hub that distortion from welding and PWHT is not transmitted to the ring portion of the flange. Can't prove it, but seen it over and over...

EDIT: not appreciably transmitted

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

It doesn't matter if it's BEM or whatever you want to call it.

Regards

 

[r6155]

See

https://www.enerpac.com/en-us/od-mo.../outside-mount-flange-facing-machines/MM300E.

 

[KernOily]

Hi guys. Sincere apologies, this exchanger is a type BEU.

The original fabrication was PWHT'd due to the thickness of the shell. I do not know if the manufacturer machined the flange face after PWHT was completed. I'm just trying to ensure the repaired flange face remains coaxial with the shell. Thanks!

 

[Christine74]

I think that re-welding the shell flange to the shell cylinder is more likely to result in the flange face moving out of plane than PWHT of the shell would, even if you're using a localized PWHT. Especially true given the size of the weld (1.531") and the required heat input to make that weld.


-Christine

 

[KernOily]

Christine - OK thanks. Let me work this with the repair shop. I will see if the shop can develop a new CRA weld overlay procedure that can be done in the vertical to repair the flange face. Thanks for your input - much appreciated!

 

[r6155]

Any photo?

Regards