Cracks in Heater outlet elbow

[himesh]

We have a three pass heater which we online spall using BFW.  It has been in service for less than three years.  The first elbow out of each pass is 9 chrome base metal with stellite overlay.  One of these elbows was found to have multiple cracks with one through wall.  We suspect that the cause may be associated with the thermal swings that occur during spalling coupled with the stellite OL.  Has anyone else had similar problems?

[B P]

I’m not an exert, but I think a 4-way cross piece at each pass outlet would possibly be a better approach than an elbow.

[Claus Graf]

I have a few questions:
1. Is this cracked elbow any different than the other two installed?
2. Who manufactured this elbow ? Was is part of the heater supply scope? Any QA/QC records available?
3. You said that the elbow had multiple cracks. Where? Inside or outside?
4. Are there any attachments to the elbow such as a elbowlet/thermowell or perhaps a piping support?
5. How does the heater coil expand? Is it fixed on the outlet side and the crossover pipes grow towards the back of the heater ? Or is it the other way around?
 
Regards
 
CG

[Claus Graf]

Here is more info, page 15:
 
http://www.api.org/meetings/proceedings/upload/BUCHHEIM_Cladding_cracks.pdf
 
Regards
 
CG

[Sim Romero]

Good idea.  A tee is frequently used in a fluid coker to avoid erosion, which is common in delayed coker spalling.

[tim gaustad]

The cracks in the pictures are so similar to our elbow that I would be surprised if it was not our elbow (Buchheim did the analysis work for us). The elbow was specified to have a stellite overlay but I could find no specification outlining how. Analysis indicated that there was no butter pass which resulted in the cracking.

[Author]

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