Hello,

The FRA 1472 day inspection criteria allows for super heater flues to remain in place if they are in good condition.

My question is, has anyone observed stress cracking at the interface of the flue to the rear tube sheet as shown in the attached photograph ?

Thank you,

Dave Griner

Note: The photograph is not of a super heater flue.

Looks to me like the issue might stem from the tube being over-rolled creating a stress riser just inside the tube sheet. A troublesome tube that just won't seal up and an adamant boilermaker's apprentice can over-roll a tube fairly quickly.

This cracking, in this area, is common in most firetube boilers in industry. The typical Scotch Marine design that is now commonplace is used industry-wide, and I have seen this failure quite often. It is not necessarily a locomotive problem.

Greetings:
In my opinion, it would be difficult to over roll an 8 gauge, 5-1/2" flue.
We had a brand new 5-1/2" 8g flue that we had trouble getting tight and re-rolled it a couple of times. The last time we stalled a good IR vane type corner motor with a No.4 Morse hole. We ended up getting it tight with a beading tool and a No. 400 air hammer.
J.David

Wouldn't a tube that is overrolled be larger than the expanded taper at the end of the flue? This end appears to have a reduced diameter with a sharp shoulder at the inner point of rolling -- I'd almost be surprised NOT to see a stress raiser form in that zone (look at the silhouetted profile across the top of the sample)

The type of failure appears unusual to me for a flue, where the inside pressure is dramatically lower than atmospheric. What accounts for the apparent bell-mouthing of the crack area?

Prossering?

I think there must have been something beyond simply overrolling going on in this case, perhaps water chemistry or the batch of steel.

.

Looking closely at the pic. It appears to have a crack in the rolled area just to the right of the split. Steel defect?