Use of deformed tubesheet
Use of deformed tubesheet
(OP)
We have two tube fixed flat circular tubesheets of boiler which are deformed due to excessive differential expension during operation. Maximum deflection of about 2 inches is around central flue gas pipe.The material of tubesheets is carbon steel and per NDE report the condition of material after deformation is unchanged i.e hardness and thickness are intact.
We intend to repalce the damaged central flue gas pipe and replace the damaged tubes and use the tubesheets as it is. The tube holes in the tubesheet shall confirm to TEMA standards and the tube to tube sheet joints shall be strength welded with light expansion. After completion of all welding, Boiler will be PWHT and pressure tested.
Could any one with similar problem share his experience and thoughts.
We intend to repalce the damaged central flue gas pipe and replace the damaged tubes and use the tubesheets as it is. The tube holes in the tubesheet shall confirm to TEMA standards and the tube to tube sheet joints shall be strength welded with light expansion. After completion of all welding, Boiler will be PWHT and pressure tested.
Could any one with similar problem share his experience and thoughts.





RE: Use of deformed tubesheet
RE: Use of deformed tubesheet
Tube holes size will be to suit the tubes. Tube holes with over tolerances will be machined after weld build up. As specified before all holes will be within TEMA tolerances.
RE: Use of deformed tubesheet
RE: Use of deformed tubesheet
RE: Use of deformed tubesheet
Can you comeback with you dimensions; tube size, tubesheet thickness, tubesheet material , etc.
You probably already have a plan of attack however I think a little discussion would benefit a lot of members.
RE: Use of deformed tubesheet
We would try retube the holes at highest deflection.In order to minimize problem in of alignment of holes, we are also planning to straighten the tubesheet by applying hydraluic jacks with end plates to distribute the load and reduce the deflection.
The thickness of tubesheet is 1.25 inch x 94" dia with 42 " opening at centre to weld the flue gas pipe.The material is SA 516 GR.70N. The tube sheet is with radiused hub butt welded to shell and bevel welded to channel side. Excessive deflection was due to malfunction of instrument and not due to normal operation.
RE: Use of deformed tubesheet
Why not just replace them?
Brian
RE: Use of deformed tubesheet
Do I understand you in that you are going to jack against the end (cover) plates?
Have you checked the tubeside of the tubesheet, especially for cracked ligaments?
Is the flue gas pipe removed?
How many tubes will you be jacking against?
The tubes will bow as they have to take up 4" if they didn't pull out of the tubesheet when it deformed.
RE: Use of deformed tubesheet
Jacking will be done against the dished head cover. Tube sheet is checked all over with UT and meets code requirements.
Flue gas pipe and all tubes in upper portion are removed and there will be no jacking against the tubes.
RE: Use of deformed tubesheet
RE: Use of deformed tubesheet
RE: Use of deformed tubesheet
Diddhed head with channel is butt welded to tube sheet
RE: Use of deformed tubesheet
Your problem is getting more complicated with each post. I'm not seeing how you can push against the upper half of the donut with enough force to move the tubesheet.
Can you post a picture or two?
http://www.tinypic.com/
or
http://www.flickr.com/