HP Heater Repair Question

[CobusvanJ]

Hi,

Our client, a power station operator, has requested us to repair their HP Heaters. Wall thickness measurements have shown the shell to be very thin (13mm) in an 1m x 0.7m area, and on the heads.

They have stated that we should do a weld overlay on the thin area, but I am not so sure about the solution, especially being 0.7m^2 in area which in my opinion will lead to excessive heat input into the shell.

A second option would be to cut out the affected area and replace it with a rectangular section. My investigations into this proposed solution thus far has not shown any HP Heaters to have been repaired in this way, only LP Heaters.

Third option, which in my opinion is the only solution, is to cut out the whole affected strake, and replace with a new one.

Can anyone please advise on what methods of repair are allowable?

HP Heater Data:
Shell Side
Design Pressure -1/22 bar
Design Temperature 420deg C
Diameter 2100 mm
Length 9450mm
Starting wall thickness 20 / 40 mm
Material 15Mo3 / 17Mn4

 

[metengr]

CobusvanJ;
Given the size, shell geometry and material, an external weld overlay is feasible as a shell repair. The external weld overlay has been endorsed by ASME Post Construction Committee in a published guideline, and it is also an endorsed repair method in the 2007 edition of the National Board Inspection Code with limitations. Essentially, the method consists of building up the shell OD surface based on the extent of internal wastage provided there are no cracks or elevated temperature concerns.

In my opinion, the flush patch repair is probably the most feasible for the shell itself given the operating conditions of this heater. For the heads, I would consider a local weld build-up. There is more effort required for ensuring flush patch alignment, full penetration welding and nondestructive testing. This is not uncommon and has been done on HP feedwater heaters and LP feedwater heaters. You need to make sure the corners are well rounded for a flush patch repair.

 

[rmw]

You didn't tell us much about the heads, whether they are fabricated or forged and what the pressure rating is. On a HP heater, I assume forged. I would only do a weld overlay there. If it is a forging, you have less worry about heat.

In any case, I concur with metengr in the advice he (I have always assumed he is a he) has given. I likewise have done both types of repairs, but I think I would do the patch on the shell.

I think it would also be faster to do the patch than doing that much overlay to that thickness. I am assuming that you are planning to get the patch pre-rolled to the required diameter.

Also, where is the thinning and what is the root cause? If it is where I think it might be, it is right adjacent to and slightly below the drips inlet where the splash impinges on the shell as it ricochets off of the bundle impingement plate (plan to replace that too), you will get continued wear on that spot in the future so a good repair that will not suffer in the future is recommended. If that is the location of the thinning, you might check just opposite the defect area for thinning on the other side at about the same elevation as well.

I don't think replacement of the entire shell course in that area is required. Your option 2 has been done many times, but unfortunately there probably aren't any links on the Internet that I could send you to and my only evidence is old photos which I couldn't find last evening for some other reason.

Good luck,

rmw