Sulfreen Condenser Problems

[rustbuster]

Hi all, I have a Sulfreen Condenser that has failed after 10 months service. Failures are in the seal welds of the inlet tube to tube sheet welds. 660 psig BFW shell side, tail gas tube side with very little evidence of corrosion.
The gas side sees temperature cycles of 300of to 600of every 15 hours.

The failures appear to be due to the migration of porosity pockets to the surface of the weld. We believe it may be due to the cyclic operation but are also questioning the original design.

Wondering if anyone has seen similar problems or offer advice in getting to the root cause.

Thanks in advance.

 

[rmw]

Do you know if at the time of manufacture if the tubes were rolled and then welded, or welded and then rolled, and how were they rolled (expanded), and can you let us know what the metallurgy of the tube, and tube sheet or tube sheet overlay material is??

rmw

 

[rustbuster]

The tubes were welded then rolled, a double groove seat, expanded 2" into the tube sheet. Tubes SA-179 x 0.130", Tubesheet 3.75" SA516-70N, no overlay.

 

[metengr]

It sounds to me that the seal welds may be suffering from fatigue cracking that either initiates at the root of the seal weld or sub-surface from the face of the seal weld. Before getting into too much detail or a conclusion, what is the service temperature for this application?

I have never heard of porosity migration in service.

 

[rustbuster]

The inlet gas temperature cycles from 300F to 600F every 15 hours, the ramp rates are gradual.

There is no evidence of cracking, I have never seen or heard of porosity migration either but the failures appear to be linked to the presence of porosity which is opening up over time / cycles.

 

[metengr]

Have you ever inspected the seal welds using wet fluorescent MT or Liquid Penetrant? Are you developing pin hole leaks in the seal weld deposit? If so, I have seen where cracks that initiate at the root (sub-surface) in seal welds can propagate to the face of the weld and when they reach the surface the crack tip results in a pin hole or multiple pin holes in appearance.

To confirm if this is happening, when you have a leaking seal weld touch grind and determine if the pin hole turns into a distinct crack which increases in length as you grind into the seal weld. This would confirm that the cracks are starting at the root of the seal weld and propagating thru the throat of the seal weld deposit.