Weld buttering for unknown CS grade

[MadieKerang]

Gents,

I have a carbon steel vessel with unknown grade and I need to repair a localized corrosion with 7mm depth and size (length & witdth) are 60 mm on the head side. Remnant thickness is 2.2mm & required thickness is 1.6mm.Nominal thickness is 9.525mm. Any rule of thumb of what type of electrode/welding material (grade?) which I can use for unknown CS grade for this repair work.

Thanks

 

[gr2vessels]

Geez, you are threading a thin ice. Is the corrosion on the head knuckle (60 mm assume from the TL)? Are you located so remotely in the north of Canada that you don't have access to a hand held spectrometer to determine the steel composition and the nameplate was eaten by bears? Do you know that the repair has to come under NBI repair R stamp? Where would you record the repair if you don't have a nameplate, to stamp it for this repair? How do you know the 1.6 mm is the required thickness? How do you know that the vessel is still operable after the repair? How did you get the 2.2 mm remnant thickness, was it correctly measured? In accordance with API 579 requirements?
Do you have an approved WPS and PQR for this type of repair? Do you intend to produce a WPS and qualify it?
Lastly, are you competent in the procedures and requirements for repair of pressure vessels? If you answer to these questions correctly, you will have the answer to the original question in the WPS/PQR.

 

[metengr]

If you are in Asia contact the manufacturer of the vessel for weld repair assistance. There are no "rule of thumb" guidelines for weld repairing vessels, as mentioned above.

 

[fegenbush]

If absolutely no information is available, would it be possible to back calculate the minimum allowable tensile strength using the existing thickness (9.525 mm)? This would at least give you the class of material required. Generally, if the material is in the 100 ksi range, you're looking at PWHT and more specialized electrodes/filler metals. If it's in the 70 ksi range, it should be a great deal easier.

 

[gr2vessels]

fegenbush, you could be on the right track.
Before you jump to calculation, first you have to establish if the material is in the 100ksi range or is in the 70 ksi range. The 3/8" thickness was selected by the fabricator, it might be oversized or not. You might end up overestimating the allowable stress. Remember, this is an old vessel, with remaining thickness of 2.2 mm out of original 3/8" plate under the defect. The OP has determined somehow the minimum thickness is 1.6 mm, without any apparent basis for this statement. Would you apply safety first on this repair, as per the recognised fittnes for service and repair standards or allow the poster to hastily weld repair the defect risking to blow up the vessel and kill potentially innocent workers.
My advice is to do the repair correctly per the current standards and you won't get hitched later on by the sheriff for harming people. They have family to support as you do.