Boiler up riser water tube failure

[mpeck1982]

Is it common for boiler water tubes to fail? I have an O type water tube boiler (1 steam drum 1 mud drum) that produces 400psig at 650 deg F superheated steam in the plant. This failed water tube was an up riser tube closest to the burner end. We capped it off and welded it. It no longer connects to the steam drum. Is this common in boiler plants? It is 25 years into its 30 yr ops expectancy.

 

[metengr]

Yes, tube failures can happen on this type of boiler. Most times a flow disturbance in the waterwall tube circuit results in reduced flow and failure from stress rupture. There could also be another possibility, under deposit corrosion. For tube failures you should have them removed and analyzed.

 

[chicopee]

What type of failure was it on that tube?

 

[mpeck1982]

Here is a picture of it. I don't know the source of failure.

 

[metengr]

Sorry, but the picture does not help me and shows some type of weld repair that was attempted based on the temper colors nearby. Next time, if you can, remove the failed tube for analysis. This is the only way to get it right.

 

[chicopee]

It is hard to tell because it appears that the weakness in the tube may have been compromised by someone prodding on that surface, however, it appears that there is a welded connection at that failure area, and if there is a welded joint than the weld had a pin hole leak probably due to poor welding.
The tube surface appears badly corroded and I would not be surprised if adjacent have the same degree of corossion. May want to chip the adjacent tube surfaces inseveral sections and smooth out those tubes surface for tube thickness check.

 

[metengr]

I wouldn't be surprised if the tube was rolled into a drum or manifold, and the leak started at a tube roll joint. It still appears as though someone tried to add weld metal on the OD surface and blew through the tube wall. Just speculation based only on the picture.

 

[rmw]

It is common for 25-30 year old boilers to have tube failures, yet it is. Actually it would be fairly uncommon for a boiler that age that had been run consistently during that time not to be experiencing failures at this point of its life.

I'd recommend that your next turnaround or outage that you do some thickness testing on adjacent tubes and go in your drums and look up and/or down each tube as far as you can see to check for scale build up. Use a borescope to look at the tubes past the bends that limit your sight line.

If this tube blew, you might be sitting on a tickng time bomb.

rmw