Strength weld between tube and tube sheet of HX

[starfarooq]

As per TEMA the grooves in the tube sheet holes are not required if tube is strength welded with the tube sheet. Can someone clarify the difference between strength weld and seal weld?

 

[SnTMan]

Easily, it is explained in UW-20

Regards,

Mike

 

[rmw]

In generic terms, a seal weld is just to seal the tube to tubesheet joint. The mechanical strength is in the roll. A strength weld does both - takes the mechanical loads and provides the sealing.

I've seen seal welds in high pressure (5000 psi) Hx's where the strength rolling was missed - a whole row of quite a few tubes in the case I am thinking of, and after ~20 years, other parts of the Hx were worn out, but the seal welded only row was still holding. Heck of a deal.

rmw

 

[starfarooq]

I have checked ASME UW-20 which gives some acceptable strength weld sketches. The two main configurations are :
1. where the tube protrudes out of tube sheet
2. where the tube end is slightly inside the tube sheet face

Which configuration is preferable with reference to future maintenance.

 

[chicopee]

A seal weld is to prevent leaking between tube and tube sheet. It has no penetration, just a surface weld. It is not to be considered a strength weld and is used when the joint between tube and tubesheet can no longer be made liquid tight after the tube end has been expanded from rolling operation.

 

[WBH]

Usually depends upon design not maintenance, sad to say. Today we try to create as much heat transfer possible in the smallest area possible. This often means tubes are spaced very close together. Having said that, the required leg size will determine the depth of the bevel, size of the fillet weld. The more common joint design is a combination of the two. This needs to be taken into account when selecting a joint design.

On a side note: strength welded tubes can have grooves and can be rolled AFTER welding. This provides two mechanical seals, normally used in lethal service or critical service as defined by the user.