WHY REPAIR WELDING IS CARRIED OUTIf there is an unacceptable defect existing in the weld region of the component in service.If there is an imperfection in the base material which when left in its place may impair the normal function of the component.Leads to failure if unattended.

REPAIR WELDINGBase material repair welding

Weld repair a) SPOT Repair b) Replacement of Joint (CUT & WELD)- With addition of Spool Piece- Without addition of Spool Piece

BASIC REQUIREMENTS OF REPAIR WELDINGBetter quality than the original weld.

Requires more care than original weld. (Since it may introduce more defects during repair)

PROBLEMS ASSOCIATED WITH REPAIR WELDINGIncomplete removal of defect.Introduction of new defect due to improper procedure, consumables, techniques.Microstructure, material or toughness degradation consumable, base material, HAZ crack. (Process Heat input)Residual stress and distortion.Unfavorable environmental conditions that are beyond control of welder, eg. Poor accessibility, position, wind, rain, fit-up conditions.

SelectProcessWelderConsumablePreheating arrangementsEquipmentsCarryout weld repairConduct NDT & CertifyRecord the above activities

APPROACH TO WELD REPAIREstablishing the cause of the initial weld defect:-Before attempting for a weld repair, know the cause and type of the weld defect already available, process and welder to be employed and other details related to the defect

II. Selection of welderUse only IBR qualified welder for Pr part weld repair.Check ValidityMaterial qualifiedPositionThickness qualifiedDiameterProcessJob configurationGenuinity of the certificate

Apart from verification of the certificate we can arrange for a mock up test for the welder & ascertain the suitability of the welder.

Do not attempt any welding if it is possible to avoid by resorting to dressing technique for defects like undercuts, notches which could be ground without affecting the performance of the components.III. Avoid welding wherever possible:-

To remove the defect positively and properly, ensure the detection of the location of the defect by using proper NDE method and mark it correctly.IV. Ensure the correct location of defect:-

Excavate a smooth and clean well shaped cavity for better accessibility by employing air arc gouging, grinding or machining.V. Make clean and smooth surface for welding:-

After the removal of defect by the above method ensure complete removal by again conducting an NDE. VI. Ensure complete removal of defect:-

Avoid introducing new defects by taking extreme care and precautions while welding by employing proper and skilled welder, good fit-up, good welding conditions, techniques, consumables etc. Use preferably flat position welding wherever possible.VII. Avoid new defects:-

There is possibility of degradation of the material in micro-structure or mechanical properties (Strength, Toughness) by employing improper filler wire, HAZ crack, process (Increase in heat input) etc.VIII. Micro-structure, material or toughness degradation:-

Due to additional welding and heat input, the residual stress may be increased, which may result in distortion.IX. Residual Stresses and Distortion:-

The conditions available for repair welding may be unfavorable viz. Poor accessibility, Awkward position, wind, rain, poor fit-up conditions etc.X. Unfavorable Environmental condition:-

Precise control of heat input during welding viz. Preheat, Postheat, during welding and stress relieving after welding will control the distortion of the components.XI. Control the heat input:-

Perform final NDE and evaluate. Ensure that the repair welding carried out is sound and defect free.XII. Final NDE:-

ECONOMICS OF WELD REPAIRDirect cost of repair welding (Welder, Consumables etc.).Additional cost of grinding, gauging, NDE, Supervision, Time, Repetition of repairs.Interruption of work schedule and the cost involved.

Generally it is estimated that the cost of repair comes to approx. to 2 to 3.5 times the original welding cost for repairing defect in a thick joint

ConclusionIBR clearance for Pr Part welding repairCarryout NDT in the defective areaAscertain the nature & location of the defectRemove the defectConduct NDT & ensure the original defect is completely removed