Tube Sheet Crack

[steamer1966]

Hello all,

We have just experienced a crack in our Waste Heat Boiler Condenser tube sheet. The crack propagates in the ligament between 2 tube holes. What would be the repair procedure for such a failure?

Any help or direction would be appreciated.

 

[stanweld]

How thick is the tube sheet; what is the material? What is the tubehole diameter?

 

[rumandcola]

Does the crack penetrate all the way through the tubesheet? Can you post any photos?

 

[ApC2Kp]

steamer1966,

Let's see, it might be a firetube waste heat boiler. Steel material A285 / A515. Tube size 2 inch. Tubesheet thickness 2 to 3 inches or more. A crack in the outlet tubesheet, upper quadrant. Maybe 20 years service on the boiler. How much of this is your situation?

Some attempt to weld repair the tubesheet. They end up chasing more cracks between ligaments. It is difficult to preheat (and PWHT) the thick tubesheet to avoid cracking of the repair weld and adjacent ligaments. More repairs of the tubesheet end up as replacement of several upper rows of the tube sheet quadrant. Big job of welding and tube replacements.

 

[AIOR]

Hi, steamer1966,

I understand, this is a repair that shall be done by R-Stamp holder in accordance with NBIC.
After 20 years of service there may a lot of invisible micro-cracks that may initiate a crack propagation after welding. Therefore, the first step should be a thorough examination using NDE methods such as MT or PT. Competent technical advice would be very helpful. May be, you have a situation where a repair is impossible or impractical.

To do repair, you may try alternative welding methods without PWHT per NBIC Part 3, 2.5.3 (page 52). For example, Method 1 includes preheat 300F (150 C) minimum at the distance of four times the depth of the repair and 450 F max interpass temperature. Method 3 which is a temper-bead welding technique, requires 350 F preheat and 450 F postweld heating for two hours. This repair is not an easy one. Good Luck!

 

[metengr]

Agree with above. The first sign of ligament cracking implies either a local problem OR the beginning signs of a much larger problem where the tubesheet has reached an end of service life condition.

I would conduct both surface and UT evaluations of the tubesheet before I would weld repair.

 

[unclesyd]

You will need to get an experienced NDT technician to do the testing.

I would also lightly grind some clear areas on the bundle face, if that's where the crack is the widest, and immediately do a PT test while the metal is warm.
If possible I would look at the shell side to the tube sheet.

Could you comeback with a little more information on your tubesheet\tube bundle design and physical conditions.

A picture or two would be great.

 

[DG72]

I don't believe that UT is feasible, since the tubesheet is perforated. Regarding a repair, you will likely be chasing cracks all day. About the time you think you have found the bottom of the crack, it spider webs to a larger mess of cracks. Hopefully, your schedule will allow replacement.