Drum and Header Weld Repair 1

[jonasinc]

What are the welding practices for a weld repair of corroded away or cracked weld at the ID of a 1 in. thick carbon steel boiler drum? What should be the preheat and the post weld heat treatment and stress relief? Can a temper bead welding be a substitute for any preheat or port weld heat treatment? Any Codes and procedures to reference?

Lee

 

[metengr]

For boilers, the recommended in-service repair code is the National Board Inspection Code (NBIC). In the 2001 Edition, 2003 Addendum of the NBIC, are guidelines for performing weld repairs to material containing defects and alternative weld repair methods - such as the temper bead method to avoid PWHT. We have even included in the NBIC local PWHT of repair areas in certain cases, similar to the “bulls-eye” method – see part RD.

All weld repairs are to be performed in accordance with the requirements in the NBIC Part RC, and the original code of construction - in your case ASME B&PV Code Section I. If the boiler was manufactured to a different code, this is acceptable, and must be referred to for information like preheat and post weld heat treatment requirements, if applicable.

For a corroded region in the drum, you should first determine the cause of the corrosion prior to performing any weld repairs. The repairs can be something as simple as a local weld overlay or weld build-up to restore wall thickness.

To repair a crack, the crack must be removed, and the excavation weld restored. Now, you have several repair options. You can select an alternative repair method, like method 1 in Part RD of the NBIC, which is an elevated preheat weld repair with no PWHT. The temper bead repairs are directed for P-No 4 and P-No 5 base material, and in some cases P-No 1 and P-No 3 base material for fracture toughness applications.

All post repair inspection requirements must be performed in accordance with the NBIC and the original code of construction, if applicable. For Section I boiler drum repairs, the post repair inspection would be either wet fluorescent MT and/or UT, depending on the extent of the weld repair.

Any weld repairs to boiler components under the administration of ASME B&PV code, Section I must be performed by a repair organization that holds a current National Board Certificate of Authorization to Repair Boilers and Pressure Vessels.

 

[jonasinc]

NBIC allows repair welding without post weld heat treatment, however, the welding procedures are not described (Parts RC and RD). Where would one find the procedures and is one of them temper bead welding?

Would temper bead welding be applicable to a boiler drum ID corrosion groove and stress corrosion at the original weld area repair? From the repair geometry of approximately 1 x 5 inch cross-section and several feet in length, it seems that temper bead would not be able to produce residual compressive stresses at the ID surface.

Also, how would a preheat temperature be maintained during welding inside a 3 foot diameter boiler header with the welder inside for hours?

Would you please give us a few names of a welding specialist who could address the above concerns?

 

[metengr]

Ok. The weld procedure you will need for your carbon steel boiler drum repair is indicated in Repair Method 1 of part RD in the NBIC. This repair method can be used on P-No 1 carbon steel base material with a local preheat of 300 deg F. Follow the instruction in Method 1 of part RD to determine the size of the area to be preheated. This instruction is given based on a 4” wide band or heat band based on material thickness.

You will need to have an ASME Section IX weld procedure specification (WPS) that is qualified for P-No 1 base material up to the required base metal thickness of the drum with no PWHT. The welders need to be qualified for the process, filler metal and base metal thickness range.

After you have evaluated and prepared the ID surface of the boiler drum for welding - including NDT to assure defect removal - I would suggest using electric resistance heating elements for the application of preheat and place them around the area of the drum you intend to repair. Yes, it will be hot (300 deg F) because the repair area needs to be maintained at 300 deg F at all time during welding so the welders need to have protective blankets or mats placed around the perimeter of the repair area to lay on with air movers to provide cool, fresh air. I would rotate the welders in and out as frequently as possible to prevent heat exhaustion.

Use low hydrogen weld rod for the repair - E7018 H4. After the welding is completed, blend grind in preparation for a wet fluorescent MT for final acceptance of the repair.