Surface Condenser Leakage

[Simdro]

Hi All,

I have a big problem and sincerely I do not know how can I solve it.

I'm talking about a surface condenser for Power Generation Plant which condense the steam coming from the turbine outlet.
The project involve an existing condenser which has worked since 20 years ago. So my company decided to revamp the Plant and consequently restore the above mentioned condenser.
The condenser was inspected and examined by a specialized company which provided to carry out a careful tube thickness survey but did not perform any test on water box tube side in particular shell(carbon steel with internal painting) and flanges(rectangular angle flanges, see the attached sketch).
As I know a lot of tube were replaced and to carry out the tube replacement the water boxes were removed together with relevant gaskets.
After tube restoring the water boxes were positioned and bolted using the new gaskets (rubber gasket with very low hardness) and consequently the tube side condenser was hydrotested at a test pressure of 5.5 bars(a).
As you may understand the tube side condenser leaks around the sealing surface of rectangular water boxes flange.
I did not see the sealing surface of rectangular flange but I can image that it will be damaged by the corrosion attack.

Any suggestion on the abovementioned matter would be highly appreciated.

Please take also into account that the plant has to run very soon and so the management probably will decide to carry out a restore without to remove the water boxes. So the operator will go in the condenser thru the manhole and could operate the repair directly from the inside of condenser.

Thank you bye bye

 

[metengr]

Simdro;
During reassembly of the waterbox, was the gasketed surface checked for flatness and cleanliness before bolting? Also, was the waterbox flange bolted using a procedure for tightening sequence and torque?

Attempting to further tighten the flange bolts to stop leakage may result in more problems. I would also avoid trying to seal the joint locally using a joint compound.

At this point, if you do not know the answers to the questions above and the joint leakage is significant you should have the waterbox removed, the flange surface checked for flatness and reassemble with a proper bolting procedure.

 

[Simdro]

First of all,
thank you very much for your prompt reply mantengr.
As I have already told you the water box parts were not taken into account during the above mentioned inspection survey including the gasketed surfaces.

Moreover I'm sure that the tighteming procedure was not used during flange bolting.

I perfectly agree with you to remove the waterbox and so on, but as I have specified in my thread at this stage is very critical to perform the aforementioned restoring procedure

Quote
At this point, if you do not know the answers to the questions above and the joint leakage is significant you should have the waterbox removed, the flange surface checked for flatness and reassemble with a proper bolting procedure.
Unquote

I know just one thing that we cannot deliver an equipment which is not still passing the Hydrotest.

Furthermore the proposed restoring procedure should be applied to N°8 (eight) waterboxes involving a lot money and time.

As additional information please take into account the attached pictures which shows the bolts used to tight the flanges.

I hope I have been a little bit more clear than before.
Cheers.

 

[metengr]

Simdro;
I am not sure what you are looking for in terms of suggestions. You have only two choices - either attempt to stop the waterbox flange leakage by using a quick fix option (loosen the flange bolts and insert a silicon compound to locally seal the leak or increase the clamp load on the flange bolts) or remove the waterboxes and start over. The quick fix option is risky but I have seen it done in the past with limited success.

 

[Simdro]

OK mentengr,

what do you want to say with "limited success"?

Do you have any historical documents or any expirience on the matter?

For "suggestion" I would like to know some confident quick fix options that I could use on my Condenser.
As I know the best thing is to remove the waterboxes but maybe it will not feasible, so I have to find alternative methods.

Thanks again...bye

 

[rmw]

Limited success means 'sometimes it works, sometimes it doesn't' (I suppose, putting words in metengr's fingertips.)

Since you seem not to be able to remove 8 waterboxes, if I were you, I would follow the process outlined by metengr above (loosten the bolts and try sealing it with gasket sealer and retightening the bolts).

I suspect that your bolts might be overtightened which is warping the waterbox flanges. Relaxing the bolts and starting over with the proper torque and torque-ing pattern might get you there.

rmw

 

[rmw]

And Simdro, why are you hydro testing at 5.5 bar? The maximum allowable workng pressure is shown on the drawing as 30 psig (~2 bar)?

No wonder the gaskets won't hold the water back. Plus, I'd stand well clear of those old water boxes at that pressure.

Plus, I love the mix of english and metric units on the dwg. That must have been a struggle for those guys back in 1971.

rmw

 

[Simdro]

rmw,

you are right about the hydrotest pressure. In fact the waterboxes are tested using equal or less than 2 bars.

As I have already underlined you on my previous thread the waterboxes shell and flange could result to thin to sustain the local loads achieving a deflection that probably does not help the sealing.

So I am not confident to seal the leakage
using the proposed gasket sealer but I totally agree with you to proper tight the bolts using a suitable procedure.

Moreover I remind you the probably the mating surface waviness could be very high due to the fact that the condenser has worked since 1971 and the abovementioned surfaces were not restored.

Simdro