Suspected failure of Tube-to-tube sheet expanded joint 1

[Rizwan.O.]

Hello Experts
We are facing a tube leakage issue in one of our 7 water-tube boilers. The issue has raised in the newest of all (around 10 years in service). Basically, the tubes in the vicinity of burner are dripping with water when hydro tested at only 5 bar. The designed pressure of the boiler is 32 bar while it has a capacity of 10 tons per hour of steam generation. No leakage is found yet and the procedure (plugging and water fillling) for individual tube testing has been done. It is suspected that expanded joint(s) got failed. The boiler only produces saturated steam (superheating unit not installed). The burner installed is a dual fuel burner i.e. Natural Gas and HFO. Also the boiler is a 2 pass boiler.
Now, the reason why I am asking for the expert advice is to get answers to the following questions:
What could be the possible reason(s) for this failure?
Which standard/SOP/article/clause can help us rectifying the issue?
And what should be the corrective action plan to prevent such failures in future?
Thanks a lot
Regards
Rizwan

 

[0707]

The video is not very clear, termal diferences between tubes and expanded joints, led the tubes to fail, maybe the external isolation of boiler needs to be improved, more information would help let us know your feedback.

luis

 

[Rizwan.O.]

I appreciate your response luis
Sure I will get some more details and will share with you soon.
In the meantime, I would like to know that what could be the possible reason of thermal difference between tubes and expanded joints. What type failure, in your opinion can cause such effects?
Waiting for expert opinion.
Thanks a lot

 

[EdStainless]

First are your firing rates and water flow rates all withing specification?
Are all of your heating and cooling rates within the recommended ranges?
Differential thermal stresses are the most likely reason.
If it was a material or manufacturing issue I would expect to see it much sooner.
Look very carefully to make sure that there are no cracks.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Rizwan.O.]

Thanks EdStainless
Will definitely look upon your highlighted concerns.

 

[georgeverghese]

Vanadium in residual fuel oil is a known corrosion agent in fired heater tubes. See if you can find a demetallized fuel oil or a lighter fuel oil with no vanadium in it.

 

[Rizwan.O.]

We generally try to run our boilers on Natural Gas. Only when gas shortage happens, HFO is the secondary available option.

 

[MJCronin]

In my opinion,...

Tube/tubesheet failures in a single area of a watertube boiler is most typically due to one of two reasons:

1) Lack of flow (and therefore cooling) in the failed tubes thereby causing excessive expansion and failure

2) Some kind of misaligned firing.. a broken or poorly repaired burner, perhaps ... again causing excessive tube expansion

( The fact that the failing tubes are in the "vicinity of the burner" significantly points to a malfunctioning burner)

You have not told us much boiler information, yet you expect immediate and correct answers..... for free ...

Some questions:

a) What is the tube size, material, location of the failures within the boiler ?
b) Who is the boiler vendor ?
c) How many tubes have failed ?
d) Have you recently hired some new 20 year-old Boiler Operators from the quick-food shop ?

Tell us more .... Give us boiler drawings ...... Participate in YOUR OWN SOLUTION !!!!


MJCronin
Sr. Process Engineer

 

[0707]

Rizwan.O.

In addition to the poor information in your video, I assume you have corrosion fatigue that started in the tube membranes on the cold side of the boiler, due to the cyclic actions of the equipment stopping and starting. So I asked if you had good thermal insulation on the cold side of the boiler. The link below will help my argument.

https://si-materialslab.com/metallurgical-lab-case-study-corrosion-fatigue-in-waterwall-tubes/

regards

luis

 

[Dhurjati Sen]

There could be issues regarding the integrity of the burner.
Flame impingement on the tubes could have happened.
Proper burner management is what you need.

DHURJATI SEN
Kolkata, India