Weld repairs can be divided into two specific areas:

1. Production repairs
2. In service repairs

The reasons for making a repair are many and varied. Typically, they range from the removal of weld defects induced during manufacture to a quick and temporary running-repair to an item of 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.

With planned maintenance and refurbishment, sufficient time can be allowed to enable the tasks to be completed without production pressures being applied. In contrast, repairs are usually unplanned and may result in shortcuts being taken to allow the production program to continue. It is, therefore, advisable for a fabricator to have an established policy on repairs and to have repair methods and procedures in place.

The manually controlled welding processes are the easiest to use, particularly if it is a local repair or one to be carried out on-site. Probably the most frequently used of these processes is manual metal arc (MMA) as this is versatile, portable and readily applicable to many alloys because of the wide range of off-the-shelf consumables.

Repairs almost always result in higher residual stresses and increased distortion compared with first time welds. With carbon-manganese and low/medium alloy steels, the application of preheat and post-weld heat treatments may be required.

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:

1. Can structural integrity be achieved if the item is repaired?
2. Are there any alternatives to welding?
3. What caused the defect and is it likely to happen again?
4. How is the defect to be removed and what welding process is to be used?
5. Which non-destructive testing (NDT) is required to ensure complete removal of the defect?
6. Will the welding procedures require approval/re-approval?
7. What will be the effect of welding distortion and residual stress?
8. Will heat treatment be required?
9. What NDT is required and how can acceptability of the repair be demonstrated?
10. Will approval of the repair be required – if yes, how and by whom?

Although a weld repair may be a relatively straightforward activity, in many instances it can be quite complex and various engineering disciplines may need to be involved to ensure a successful outcome.

It is recommended that there be an ongoing analysis of the types of defect 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:

1. A detailed assessment to find out the extremity of the defect. This may involve the use of a surface or sub-surface NDT methods.
2. Cleaning the repair area, (removal of paint grease etc).
3. Once established the excavation site must be clearly identified and marked out.
4. An excavation procedure may be required (method used ie grinding, arc-air gouging, preheat requirements etc).
5. NDT should be used to locate the defect and confirm its removal.
6. 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.
7. Use of approved welders.
8. Dressing the weld and final visual.
9. NDT procedure/technique prepared and carried out to ensure that the defect has been successfully removed and repaired.
10. Any post repair heat treatment requirements.
11. Final NDT procedure/technique prepared and carried out after heat treatment requirements.
12. Applying protective treatments (painting etc as required).
    (*Appropriate’ means suitable for the alloys being repaired and may not apply in specific situations)