Repair welding of vessel overlay
Repair welding of vessel overlay
(OP)
I have a carbon steel 75.0mm thick pressure vessel with a 3.0mm 904L overlay. Internal inspection has revealed a pit defect in the overlay with a diameter of 5.0mm and a maximum depth (taking account of measurement uncertainties) of 2.5mm.
The vessel was heat treated during construction.
I have a weld overlay procedure with a max interpass temp of 135degC and a preheat temperature of 50degC using a propane torch.
The question is: How likely is it that the carbon steel shell at the weld location could experience temperatures close to the lower critical temperature?
The vessel was heat treated during construction.
I have a weld overlay procedure with a max interpass temp of 135degC and a preheat temperature of 50degC using a propane torch.
The question is: How likely is it that the carbon steel shell at the weld location could experience temperatures close to the lower critical temperature?





RE: Repair welding of vessel overlay
Per your stated conditions, most likely you will have a zone of heat affected material in the carbon steel base material at the location of weld repair. By my calculations, you only have about .5mm (0.020") of remaining weld deposit, which is not enough material to avoid contact with the carbon steel substrate.
What are your service conditions that would allow you to use a temper bead type weld repair with elevated preheat? Do you have any specific hardness requirements for the carbon steel base material because of corrosion concerns related to process conditions?
RE: Repair welding of vessel overlay
If you are concerned with meeting NACE MR0178 hardess requirements in the P-1 HAZ, I would advise the use of a welded mockup and measure hardness in the HAZ of the carbon steel base plate. In selecting base plate for the mockup, try to obtain it with a carbon equivalent as near as possible to, or greater than that of the vessel plate.
RE: Repair welding of vessel overlay
One of our Metallurgists is happy with the weld procedure described above due to the small area to affected and that the area will be filled with two parallel runs.
What we have noticed is that the heat sink is such that after the 50degC preheat is applied the surface cools in seconds.
We have taken a wall thickness measurement from the outside and the reading is 81.0mm, how much of that is carbon and how much is overlay is not determinable, however we are sure that there is more than 0.5mm of the linning remaining.
RE: Repair welding of vessel overlay
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Repair welding of vessel overlay
RE: Repair welding of vessel overlay
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Repair welding of vessel overlay
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Repair welding of vessel overlay
The base metal is Superelso 500 and the CE is between 0.4 & 0.45 and the 3mm clad 904l. The cladding was subjected to the PWHT. The degradation of the cladding by the PWHT process is minor in terms of the corrosion resistance requirements.
I am the certifying authority and as such am not too concerned about the possibility of SCC or HIC as once the cladding has been restored there is no possibility of chlorides or Hydrogen reaching the base metal. What does concern me slightly is the long term effect of a local hard spot. I have asked for a mock up weld to and get macros & hardness.
The defect that is being repaired is an original fabrication defect that was picked up during the vessels 1st routine inspection.
Jim
Principle Mechanical Eng
RE: Repair welding of vessel overlay
RE: Repair welding of vessel overlay
RE: Repair welding of vessel overlay
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/