welding repair procedure and method statement pdf


Procedure for welding repair

Weld repairs can be divided into two specific areas:
1. Production
2. In-service

The reasons for making a weld repair are many and varied (can be due to manufacturing defects or in-service failure) and involves the removal of weld defects induced during manufacture to a quick and temporary running repair to an item of the production plant.

In these terms, the subject of welding repairs is also wide and varied and often confused with maintenance and refurbishment where the work can be scheduled.

Click here to Get Guide on How to Weld various materials

Sample Welding repair procedure.pdf

Factors to be considered before starting the welding repair?

There are a number of key factors that need to be considered before undertaking any repair. The most important being a judgement as to whether it is financially worthwhile. Before this judgement can be made, the fabricator needs to answer the following questions:

• 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?
• Which NDT method is required to ensure complete removal of the defect?
• Will the welding procedures require approval/re-approval?
• What will be the effect of welding distortion and residual stress?
• Will heat treatment be required?
• What NDT is required and how can the acceptability of the repair be demonstrated?
• Will approval of the repair be required – if yes, how and by whom?

Steps for the welding repair?

The weld repair may seems relatively straightforward activity, although it can be quite complex and various engineering disciplines may need to be involved to ensure a successful outcome. It is recommended that ongoing analysis of the types of defect is carried out by the QC department to discover the likely reason for their occurrence (material/process or skill related).

In general terms, a welding repair involves:
• A detailed assessment to find out the extremity of the defect. This may involve the use of a surface or sub-surface NDT method.
• Cleaning the repair area, (removal of paint grease etc).
• Once established the excavation site must be clearly identified and marked out.
• An excavation procedure may be required (method used ie grinding, arc/air gouging, preheat requirements etc).
• NDT 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.
• Use of approved welders.
• Dressing the weld and final visual.
• 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.

Production repairs, Analysis & Assessment

Repairs are usually identified during production inspection. Evaluation of the reports is carried out by the Welding Inspector, or NDT operator. Discontinuities in the welds are only classed as defects when they are
outside the range permitted by the applied code or standard. Before the repair can commence, a number of elements need to be fulfilled.

Analysis
As this 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, however, if the defect is lack sidewall fusion this can be apportioned to the lack of skill of the welder.

Assessment
In this particular case, as the defect is open to the surface, magnetic particle inspection (MPI) or dye penetrant inspection (DPI) may be used to gauge the length of the defect, and ultrasonic testing (UT) used to gauge the depth.
A typical defect is shown below:

Excavation/ Removal of welding defect:

If a thermal method of excavation is being used i.e. arc/air gouging it may be a requirement to qualify a procedure as the heat generated may have an effect on the metallurgical structure, resulting in the risk of cracking in the weld or parent material.

To prevent cracking it may be necessary to apply a preheat. The depth to width ratio shall not be less than 1 (depth) to 1 (width), ideally, 1 (depth) to 1.5 (width) would be recommended (ratio: depth 1 to width 1.5)
A side view of excavation for a slight sub-surface defect is given below:

Cleaning of the Excavation & confirmation of defect removal

At this stage grinding of the repair area is important, due to the risk of carbon becoming impregnated into the weld metal/parent material. It should be ground back typically 3 to 4mm to bright metal.

At this stage, NDT should be used to confirm that the defect has been completely excavated from the area. Usually, Penetrant testing & magnetic particle testing are the NDT method used for this purpose.

Re-welding of the welding defect area:

Prior to re-welding of the excavation, a detailed repair welding procedure/ method statement shall be approved. Click here to dowload General-repair-procedure-for-welds You can modify it to suits your requirements.

NDT confirmation of successful repair

After the excavation has been filled the weldment should then undergo a complete retest using the same NDT techniques as previously used to establish the original repair. This is carried out to ensure no further defects have been introduced by the repair welding process. NDT may also need to be further applied after any additional postweld heat treatment has been carried out.

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