Seal Welding and Strength Welding 1

[Merzi]

Can anyone please explain the difference between seal welding and strength welding of heat excahnger tube to tube sheet joints.

As far as i understand Strength weldg is determined by performing a mock up of the joint followed by push out test.

 

[metengr]

Yes. However, instead of me trying to paraphrase the words in ASME Boiler and Pressure Vessel Code, Section VIII, Div 1, Part UHX, I suggest you review it. Specifically, review UHX, section UHX-15 Tube-to-Tubesheet Welds.

 

[deanc]

Merzi:

Have you looked at UW-20?

 

[DG72]

A seal weld is provided for "additional leak tightness only". Often times for seal welds, the tube is welded to the tubesheet without the addition of filler metal (although, filler metal is sometimes used, especially for some metallurgies like 410 stn. stl.) The tube normally projects beyond the face of the tubesheet 1/8". So, when the tube is welded, it melts and fuses to the tubesheet. The tube hole in the tubesheet is not beveled for a seal weld.

A strength weld is provided "to carry longitudinal tube loads", and it also provides additional leak tightness. The procedure is essentially the same as a seal weld, except the tube hole in the tubesheet is beveled (ie. 45 deg bevel or j-groove) to allow filler metal to be deposited. Generally, this is a 2-pass weld.

 

[DG72]

Also, ASME Sect. VIII, Div. 1 doesn't specifically give rules for qualifying tube to tubesheet welds, so most people use Div. 2 for qualifying strength welds. Some would suggest that it must be qualified as a partial groove weld; however, most still follow Div. 2.