Is PWHT required for Saddles / Supports of a Vessel along with Main Vessel

[DK44]

A Shell of a Shell & Tube Heat Exchanger is constructed of CS or LAS MOC requiring PWHT as per Code. Saddles / Supports constructed of CS structural weldable quality are attached by welding to it.
Shell MOC : CS or LAS
Saddle wrapper pate MOC same as Shell.
Saddle ribs etc MOC : CS structural weldable quality.

1. Is PWHT of such saddles / supports required along with the main vessel. Some times the PWHT temperature for CS saddles may be high due to main Vessel requirement.

2. Can the saddle wrapper plate be welded to Shell and PWHT along with Shell and then CS Ribs etc of saddle / Supports are welded without further PWHT.

3. However,if such above PWHT for Supports / Saddles is not necessary but done, is it detrimental to CS materials of the Saddles / Supports.

 

[SnTMan]

DK44, 1. Saddles are not within Code scope. PWHT would not normally be required although if constructed of unusually thick material and full penetration welded or welded with large fillet welds it might be advisable. Note saddles are normally fillet welded with rather small fillets, say 1/2" or less. Some structural Codes or welding Codes may further specify.

2. Yes

3. Normally not for CS

Regards,

Mike



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

 

[DK44]

Thank you SnTMan for your response.

1. There is a caution that no welding shall be done on the vessel after PWHT.
Does it attract the welding between saddle ribs to wrapper plate, the wrapper plate having undergone PWHT along with the shell, of-course such welding is not a direct welding on to the post weld heat treated pressure part Shell.

2. Also that the saddles provide good support of the Heat Exchanger shell in the furnace during PWHT, it is preferred by the vendors to put the Shell + Saddles inside the furnace and do PWHT together. Is this detrimental to the CS saddle especially when LAS shell is PWHT at 690 C, the CS saddle also sees that temperature.

 

[SnTMan]

DK44, 1, this caution is commonly intended to apply to the pressure boundary only.

2, I doubt it is detrimental, this construction is common, but you may want to check with a metallurgist concerning your exact materials.

Regards,

Mike

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

 

[mk3223]

Agreed that the vessel can be preferred to be PWHT together with saddle supports if the furnace is big enough.
The temperature of the PWHT is normally below the steel phase transformation temperature of the specific composition. And, the treatment is only to release the residual stress formed in the HAZ area.

 

[r6155]

Also you can PWHT the channel, this is a good engineering practice.

Regards

 

[DK44]

Thank you SnTMan, mk3223, r6155 for your responses.