Welding Inspector Weld Repairs Section 16 4/23/2007 Weld Repairs Weld repairs can be divided into 2 specific areas: Production repairs In service repairs 4/23/2007 Weld Repairs A weld repair can be a relatively straight forward activity, but in many instances it is quite complex, and various engineering disciplines may need to be involved to ensure a successful outcome. • Analysis of the defect types may be carried out by the Q/C department to discover the likely reason for their occurrence, (Material/Process or Skill related). In general terms, a welding repair involves What! 4/23/2007 Weld Repairs A weld repair may be used to improve weld profiles or extensive metal removal: • Repairs to fabrication defects are generally easier than repairs to service failures because the repair procedure may be followed • The main problem with repairing a weld is the maintenance of mechanical properties • During the inspection of the removed area prior to welding the inspector must ensure that the defects have been totally removed and the original joint profile has been maintained as close as possible 4/23/2007 Weld Repairs In the event of repair, it is required: Authorization and procedure for repair Removal of material and preparation for repair Monitoring of repair Weld Testing of repair - visual and NDT 4/23/2007 Weld Repairs There are a number of key factors that need to be considered before undertaking any repair: The most important - is it financially worthwhile? Can structural integrity be achieved if the item is repaired? Are there any alternatives to welding? What caused the defect and is it likely to happen again? How is the defect to be removed and what welding process is to be used? What NDE is required to ensure complete removal of the defect? Will the welding procedures require approval/re-approval? 4/23/2007 Weld Repairs Cleaning the repair area, (removal of paint, grease, etc) A detailed assessment to find out the extremity of the defect. This may involve the use of a surface or sub surface NDE method. Once established the excavation site must be clearly identified and marked out. An excavation procedure may be required (method used i.e. grinding, arc-air gouging, preheat requirements etc). NDE should be used to locate the defect and confirm its removal. A welding repair procedure/method statement with the appropriate welding process, consumable, technique, controlled heat input and interpass temperatures etc will need to be approved. 4/23/2007 Weld Repairs Use of approved welders. Dressing the weld and final visual. A NDT procedure/technique prepared and carried out to ensure that the defect has been successfully removed and repaired. Any post repair heat treatment requirements. Final NDT procedure/technique prepared and carried out after heat treatment requirements. Applying protective treatments (painting etc as required). (*Appropriate’ means suitable for the alloys being repaired and may not apply in specific situations) 4/23/2007 Weld Repairs What will be the effect of welding distortion and residual stress? Will heat treatment be required? What NDE is required and how can acceptability of the repair be demonstrated? Will approval of the repair be required – if yes, how and by whom? 4/23/2007 Production Weld Repairs Before the repair can commence, a number of elements need to be fulfilled: If the defect is surface breaking and has occurred at the fusion face the problem could be cracking or lack of sidewall fusion. If the defect is found to be cracking the cause may be associated with the material or the welding procedure If the defect is lack of sidewall fusion this can be apportioned to the lack of skill of the welder. In this particular case as the defect is open to the surface, MPI or DYE-PEN may be used to gauge the length of the defect and U/T inspection used to gauge the depth. 4/23/2007 Weld Repairs The specification or procedure will govern how the defective areas are to be removed. The method of removal may be: • Grinding • Chipping • Machining • Filing • Oxy-Gas gouging • Arc air gouging 4/23/2007 Defect Excavation Arc-air gouging 4/23/2007 Arc-air gouging features • Operate ONLY on DCEP • Special gouging copper coated carbon electrode • Can be used on carbon and low alloy steels, austenitic stainless steels and non-ferrous materials • Requires CLEAN/DRY compressed air supply • Provides fast rate of metal removal • Can remove complex shape defects • After gouging, grinding of carbured layer is mandatory • Gouging doesn’t require a qualified welder! 4/23/2007 Production Weld Repairs Production Repairs are usually identified during production inspection evaluation of the reports is usually carried out by the Welding Inspector, or NDT operator 4/23/2007 Production Weld Repairs Plan View of defect 4/23/2007 Production Weld Repairs Side View of defect excavation W D Side View of repair welding 4/23/2007 In Service Weld Repairs In service repairs Can be of a very complex nature, as the component is very likely to be in a different welding position and condition than it was during production It may also have been in contact with toxic, or combustible fluids hence a permit to work will need to be sought prior to any work being carried out The repair welding procedure may look very different to the original production procedure due to changes in these elements. 4/23/2007 In Service Weld Repairs Other factors to be taken into consideration: Effect of heat on any surrounding areas of the component i.e. electrical components, or materials that may become damaged by the repair procedure. This may also include difficulty in carrying out any required pre or post welding heat treatments and a possible restriction of access to the area to be repaired. For large fabrications it is likely that the repair must also take place on site and without a shut down of operations, which may bring other elements that need to be considered. 4/23/2007 Weld Repairs Is welding the best method of repair? Is the repair really like earlier repairs? What is the composition and weldability of the base metal? What strength is required from the repair? Can preheat be tolerated? Can softening or hardening of the HAZ be tolerated? Is PWHT necessary and practicable? Will the fatigue resistance of the repair be adequate? Will the repair resist its environment? Can the repair be inspected and tested? 4/23/2007 Weld repair related problems heat from welding may affect dimensional stability and/or mechanical properties of repaired assembly due to heat from welding, YS goes down, danger of collapse filler materials used on dissimilar welds may lead to galvanic corrosion local preheat may induce residual stresses cost of weld metal deposited during a weld joint repair can reach up to 10 times the original weld metal cost! 4/23/2007
