Boiler Tube Ruptures

Is this a dirt-fired boiler? If so, the coal ash may be a contributing factor to failure by erosion. Are the shields in place? Are they plugged? Is there a build-up of slag on the tubes? Both latter conditions will prevent proper heat transfer from taking place.

Basic ultrasonic thickness gauges are often used for quick'n'easy thickness measurments.

If your boiler is coal fired I would suspect erosion by ash carry over. The solution is baffle plates and shielding.

If the boiler is oil fired then I would be looking for possible corrosion problems coursed by high sulfur fuel oils and/or water ingress. Is you economiser exposed to rain or salt water exposure? This is a common problem with ship's economisers.

Another thing that can cause economiser corrosion is if the heat transfer finns that are fitted are a dissimilar metal to the tube. If this is the case then you can get an electrolytic form of corrosion.

Just keep telling yourself that it really is all good fun.

Measuring the tubes in place is best initially done with an electronic caliper or micrometer for the OD (Outside Diameter) and with an ultrasonic tester to measure the thickness. Once a dangerous or unacceptable diameter has been determined a go/no go gauge can be made and put on a piece of string so that if it is dropped it is easy to retrieved. The gauge is much easier to use than the measuring devise.

Another tip is to use a sheet of ply wood and lots of rag when doing this work in-place. Dimples maybe attractive on some people but not where you get them sitting on an economiser.

A periodic removal and replacement of known troublesome tubes will help to determine how often replacements should be scheduled.

BAB

There could be several reasons of economizer tube failure like

1) Erosion

2) corrosion internal

3) Corrosion external

4) Improper welding

5) failure due to expansion restriction

6) Rubbing of tubes

7) Choking of tubes

8) Secondary failure due to erosion due to nearby tube failure

9) Raw material defect

10) Thinning of tube while bending

11) Improper acid cleaning process

A metallurgical analysis of tube will reveal the reason of failure. Corrective action can be accordingly planned.

Here is a new patented composite product used just for that reason.

This application is a corrosion only problem, we have successively used this technology for gas path and supper heater erosion.

Another possible cause not metioned above is accidental overheating and pressurization by the operators.

Economiser tube failure can occur when (1) the flow to the tubes is blocked in,(2)there is no code required pressure relief device (3) boiling occurs and the operators will not confess.

Do the failures appear to be related to external corrosion or are they "fish mouthed" overpressurization failures (the long axis of the fish mouth is along the tube axis)

Many third world power plant managers would not have permitted such operational negligence.

My opinion only

This is actually not a boiler but HRSG which is connected to gas turbine fired by natural gas.

The percentage of sulphur is considered high 2.2%. therefore it could be the external corrosion which has resulted in gradual reduction in tube thickness till it failed.

but why this happened in one tube out of 124 tubes?

considering over-pressure situation this also could be possible. what is the normal pressure in these tubes?

A metallurgical analysis by a lab will tell the reason of failure. 2.2 % sulfur is likely to cause corrosion. If it is corrosion than subsequent failures will continue to be there as other tubes also will be getting corroded.
Failure happens in the weakest tube after that the pressure falls. So next time you go up in pressure next weak tube will fail.

As a boiler owner you will get all design documents. So you can look up the design pressure in that.

Once the reason of failure is known solutions are there.