Boiler Tube Leaking

One thing to check if you can come up with a boroscope (camera for inspecting flow path of boiler tubes in headers)... see if someone may have left trash (debris) or tools in the tubing header at assembly. (You say the problems have been frequent since the boiler was in operation over the last three years.) At my work place after about 15 years of operation and frequent boiler outages due to leaks, the decision was made to inspect the headers feeding the tubes water for the boiler cycle. In the process, they found many loose welding rods and a few small tools which were misplaced and consequently left in place in the headers after the boiler tubes were welded. This restricted water flow to the tubes causing overheating and subsequent failure of the tubes. Even recently, after revamping the boiler by replacing part of the components, we had a similar incident with a boiler leak. A tool from the replacement of the components was found lodged in a tube. This caused a restriction as before which caused another boiler leak in the associated boiler circuitry. This is not an uncommon problem in the industry.

My suggestion is to cut out a section of tube at the site of the leak and run a boroscope (camera in a tube) through the tubes back toward the header and determine if debris or tools may have been left in the tubes at manufacture of the boiler. If there are obstructions, determine the location and cut another observation port for access and removal. This should allow for longer run time of your boiler and extend the life of the circuitry. It may be expensive, but if done in a timely fashion, it will pay for itself many times over. (Not to mention the fact that the tool and process can be used many times in the future as the need arises.)

Rosli, lets not talk on the tubes. No Boiler will be passed unless certified on its construction materials as per designated standards. What was your Feed Water Temperature at the feed tank? Do you have a feed tank with de-aerator? Was feed water at >105C? I feel it is the O2 in the feed water that was not deaerated prior feed did the damage - "ferric oxide" .

We would like more information on your boiler leaks. Does there appear to be corrosion in the associated tubes? If so, then O2 could be the problem. Perhaps deaerator is not properly removing oxygen from feedwater as ducon suggests.

Also, you might check with the water technician (or whoever has the job) and verify that your hydrazine feed system is functioning properly (if applicable).

Where in the boiler circuitry are the leaks developing? e.g. economizer section, firebox, superheater, reheater, convection pass, roof pass? Please explain.

Are the leaks developing at welds or at some distance away from the welds or the header?

If the oversight of the installation of the boiler internals was faulty, the wrong materials could have been used, so don't rule that out just yet. These situations happen. (I would doubt that that is the case, so I suggest looking at other areas first.

If the leaks are in welds, then the wrong welding rods could have been used, or unskilled construction personnel could have been utilized in an effort to increase the profitablility of the contractor.

I also suggest hiring a good boiler engineer to go over all of these and other variables with your boiler's particular case.

Rosli, I have worked with a major utility in this application on 800mw boilers. I was responsible for making sure they didn't come down after the outages. Long story short, you definitely should check process parameters as some have already suggested. Furthermore, here are a few things we have learned: 1) Proper FME protection. Whenever we cut our tubes for a replacement, they wer inspected with a boroscope (usually a 60' olympus in longer sections). Make sure the owner AND Contractor QC check this. We capped the tube if it wasn't immediately repaired. We then color coded tape (green for a good tube) around the cap and had each QC rep initialed the top cap after inspection. 2)Prior to the tubes being welded up, make sure that they do not use excessive rice paper. It doesn't always dissolve like it should. Shavings etc can build up around there and create a hot spot which can cause a tube failure. 3) Have a certified welding inspector check and verify welds. 4) If using chill rings during welding, that can pose other issues. They work great when the bevel is right. 5) I would highly suggest renting a thermal imaging camera if you don't have one. You will sometimes notice where there seams to be hot spots or mainly temperature profile differences in the tubes. 6) Make sure the boiler tubes are the proper material. There are material guns etc that can be used their. These are only some of many QC measures that can be used to avoid premature tube failure. I hope this helps. Darin

Is your plant "base loaded" or does it cycle frequently?

Previously leaks were found at weld joints,between headers and side and front walls,portion not direcly exposed to heat.Probably welding procedure.

Recently,leaks were noticed some distance from weld joints and vertical position,closer look like small crack/pinhole leak.

As for FW temperature we,usually maintained below 105 deg C as higher will cause pump to cavitate..

I understand that O2 pitting is like small dot on the surface around maybe 1mm deep and visible on the drum suface.Is there any way we can be sure that the leak is caused by O2 pitting?Any instrument or test to check that the tube can last as recommended by the manufacturer.Can overheating cause small crack or pinhole leak?

Rosli,

As I am not an engineer, I feel unqualified to answer your overall concerns. However if you are still unsure whether your problem is due to dissolved oxygen pitting or another cause of corrosion or erosion of your boiler tubing, perhaps you can follow some of these links and get a better idea by a comparison from actual photos of other boiler leak related problems. i.e. dissolved oxygen corrosion, impingement, starving (lack of sufficient flow through tubes), etc.

http://www.coalpowermag.com/ops_and_maintenance/The-Role-of-Fireside-Corrosion-on-Boiler-Tube-Failures-Part-I_254.html

http://www.coalpowermag.com/ops_and_maintenance/The-Role-of-Fireside-Corrosion-on-Boiler-Tube-Failures-Part-II_267.html

http://www.finishing.com/2400-2599/2496.shtml

http://www.google.com/search?hl=en&source=hp&biw=1260&bih=894&q=corrosion+of+boiler+tubes&oq=corrosion+of+boiler+&aq=2v&aqi=g-v1&aql=&gs_sm=c&gs_upl=13983l36325l0l38606l20l18l0l6l6l0l282l2627l1.2.9l12&safe=active

http://www.google.com/search?hl=en&safe=active&biw=1260&bih=894&q=+O2+corrosion+of+boiler+tubes&btnG=Search&oq=+O2+corrosion+of+boiler+tubes&aq=f&aqi=&aql=&gs_sm=s&gs_upl=4237319l4244975l0l4249537l5l5l1l0l0l0l329l720l1.1.1.1l4

http://www.corrosionlab.com/Failure-Analysis-Studies/29273.oxygen.carbon-steel-tubes.htm

To be able to operate at 102C I suggest raising your DA tank to a height needed for proper NPSHA for your pumps if the are the proper pumps for the boiler. If they are improper REPLACEMENT pumps throw them away and install pumps that will operate at 102C.