Comb-Cyc.Tube Repair

[VAWELDER]

With the rush of combined cycle units to our area,I was wondering if anyone had any suggestions on how the tube failure's will be delt with.Being they are in a bundle setup,tube to header,how will you repair or isolate tube failure.I have heard several idea's,none too convincing.Such as cutting into header's and plugging tube from both sides.Keeping in mind most of your tube and header joints are P-91&T-91,(requiring purge)Then welding window back in,also requiring purge.Other than that how will you even locate tube leaks.Anyone having worked on these new units have seen the tube bundles and know what I am talking about.Anyone?

 

[davefitz]

The new combined cycle HRSG's have been specifically designed with this problem in mind. A great deal of thought and effort was used to make certain that the tube repair is the most difficult and time consuing task imaginable.

If you find a way to repair these tubes in less than a week's time, let us know and we will file a complaint to the respective HRSG vendor.

 

[MJCronin]

VAWELDER, you are not he first to wonder about the amount of planning that went into maintenance repairs for P91/T91 boiler components

With the onslaught of so many combined cycle plants (CALPINE alone had massive plans for constuction of 80 power plants) it was inevitable that these units were to be slapped together by inexperienced designers and fabricators. I have heard many stories of welding shops in Mexico that have never worked on anything more complex than a bicycle frame, suddenly welding T91 with temporary farm labor.............

My thoughts only !!


MJC

 

[hrsgInspector]

It's true that these failures can be difficult to repair. However, the repairs are being (successfully) performed at many units. T-91 presents greater difficulties in achieving proper heat treatment in the field; but it can be done. This is a feature topic of the upcoming HRSG User Group Maintenance Meeting in October in California (see the HRSG User Group site hrsgusers.org).

 

[Tailleur]

Out of interest, the horizontal tube / vertical gas path HRSGs (typical in Europe) have a significant advantage in this area. These designs tend to use single inlet/outlet headers with a serpentine tube arrangement between them. The tube to header welds are generally accessible, and by cutting a hole in the casing whole tubes can be removed and replaced individually if necessary. I have some documentation & photographs of just such a procedure if anyone is interested.

 

[rmw]

Hence the saying; Cut your way in, weld your way out.

It has got to be a gold mine for someone.

The designers of these CCGT plants in general never seemed to realize that these things were ever going to need to be worked on.

When maintenance issues become realiability issues (someone is busy cutting their way in, or welding their way out) just when the grid is screaming for megawatts, the luster of the low heat rates is going to be badly tarnished, and it will be some of the old boat anchor 30-40 year old central station units that have been condemned as having too high of a heat rate to run that are going to burn the gas to save the day, to the detriment of the ratepayers, of course.

 

[swageninja]

VAWELDER,

I don't know that there is any easier way than cutting your way in and welding your way out. But with regard to identifying the leaking tube we have a tool for just this task. It essentially perform a hydro on individual tube joints by sealing in side the tube and crushing a seal against the header face or tubesheet and pressures up 3000 psi.


Best Regards, Joey

http://www.spectool.com