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Internal cracks on Boiler Steam Drum

Friday, January 28, 2011   By: Gerardo Chiapetta [1106] 1 Stars
We have a Mellor Goodwin Boiler currently in major outage. We are replacing almost all the internal tubing, insulation, repairing gas and intake air paths, etc.
During Drum inspection, several cracks have been found, and some of them already repaired. But theres particularly one indication found obtained through UT test that show a circumferential internal not superficial crack? Its located near the union welding of head to shell. Im attaching our reports and some photographs of the findings. The drum is 100 mm thick and the indication is 25 mm below internal surface.
Some say it has been there since the drum was built 1968 others say it could be an internal crack that could get worse in the future.
Now we are in the repairing dilemma. Should be left like that in order to avoid additional damage to the drum or should it be repaired?

Has anyone had some experience or event similar in your boilers?


Click on picture for full size view or to view PDF!

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Friday, January 28, 2011   By: Gerardo Chiapetta [1106] 1 Stars
Sorry, but the files are in Spanish hope you can help!


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Monday, January 31, 2011   By: Murphy [21] 4 Stars
I would like to add that a discontinuity that you found linear or round that you reject must be removed for the benefit of all. As a level-II UT NDT non-destructive testing Technician your judgment is the most important.

I agree with Ross that using radiography is very useful if it is available in country.

But if it is not, then asking for a second Ultrasound Level-II or Level-III will prove your first set of results. Certainly those in the power plant will not be convienced.

The risk of leaving the rejected discontinuity in the drum at the circumfrential joint is very-very high.

I would have the areas of interest excavated and arrange for heat treatment for the repair weld procedures .

I would guess that the boiler repair firm holds an ASME code S stamp.

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Friday, January 28, 2011   By: Ross [390] 5 Stars
I would have thought that an internal weld problem suggest it was there a long time but that does not make it okay to leave. I am thinking how we would handle it.

I am not a weld inspector but my experience is that could be a lack of weld fusion. You are in a tough spot and should tell them how you are going to classify the indication.

We would repair by grinding it out or air arc it out.

The owner will have to deal with the PWHT stress relieving.

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Friday, January 28, 2011   By: Ross [390] 5 Stars
Almost forgot. We would have an x-ray done.

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Sunday, January 30, 2011   By: N.Ramani [965] 4 Stars
Hope you would have checked the whole Drum since this could be a problem of lamination. As advised by others you cannot leave it as it is. I would suggest that you get in touch with EPRI of USA or any reputed Boiler manufacturers who could help you.

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Tuesday, February 01, 2011   By: Ross [390] 5 Stars
Are the repairs to the steam drum almost done or did the owners opt out not to repair?

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Tuesday, February 01, 2011   By: Gerardo Chiapetta [1106] 1 Stars
An x-ray was made last friday. A D7 plate was used and exposure was for about 4 hours. The x-ray didnt show anything, no indication or crack at all. An ASME consultant suggested that if the x-ray result didnt show anything, the code follows x-ray results and not UT... Its something obvious, he suggested not to repair but he wouldnt sign a paper! If he had to sign anything he would suggest to repair... Its kind of confusing right?
So, the managers and owners decision was taken: not to repair, continuing mounting tubes and keep monitoring the drum yearly. I dont quite agree with this decision but its their word, it would have taken 2 days to repair or so... Anyways, thank you all for your help and suggestions.



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Tuesday, February 01, 2011   By: Ross [390] 5 Stars
I am surprised the consultant would not agree when at least an RT Level-ll NDT tech looked at the x-ray and evaluated. Remind me not to suggest him.

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Sunday, February 06, 2011   By: Murphy [21] 4 Stars
Having RT done on the steam drum was the best decision and when the film shot does not show an indication the decision seems sound.

Whether round or linear and using the same acceptable criteria of ASME Section One and Section -Nine as well as that of Section Five to that to which the boiler was built.

When a Level-3 RT establishes a written procedure for the shot then after developing there is no indication then there is no indication.

But, it does not invalidate the UT especially since it is repeatable. My impression is UT found a micro-structure anomaly perhaps at the heat effect zone at the weld to base metal interface from when the head was welded to the tube sheet of the steam drum shell. Perhaps the tube sheet was to cold?

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Published on steamforum.com


High Sulfite Residual
By: Ross. [390]

First, I want to say that large amounts of Sodium Sulfite NaSO3 becomes a contaminate because it will produce foaming and other problems, but foaming is the primary problem.

Your 500-psi Water Tube Boiler is seems to have reasonable level of residual Sodium Sulfite NaSO3 remaining in the boiler water. Nice pH too.

Your 300-psi Waste Heat Recovery Boiler has twice what I would expect for Sodium Sulfite NaSO3 at ranging 80-ppm to 100-ppm. pH is good so you are getting a good yield.

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