Weld repairs are applied on an item by mutual agreement to remove weld defects during manufacturing or when the problem arises during service. A thorough assessment is recommended before the implementation of a repair as there are several factors that might influence the functioning of specific item. For example gouging is used to excavate the defective weld metal that may induce cracking in rest of the weld or parent metal. By using Arc Air gouging, carbon may detach from the carbon rod and debase the weld properties. Many additional procedures are prepared to rectify such problems. Manually controlled procedures are quite appreciable for site or shop repairs. Following are the decisive element that are required to achieve the desired results.
Effect of welding procedure
It is essential to think thoroughly about the outcome before making decision whether the specific welding procedure fulfil the requirement without affecting the whole structure of an item under repair. As arc processes induce welding distortion and residual stresses
Required Welding procedure
Ensure the suitable procedure with appropriate details of consumable type, temperature, travel, post heat treatment if required. If the procedure requires approval, an authorized person is eligible to serve the purpose. In order to remove complexities, application of procedure must be powered by mutual acceptance and agreement.
It is stated above that repair weld may result in residual stresses and for this post repair heat treatment is applied. Special tools are available which are used for weld dressing. Choice of accurate tool is essential factor to perform various post treatments.
Non Destructive Testing
For the inspection of defects Non-destructive testing is performed in three stages of weld repair;
- Before repair weld
- After repair weld
- After final treatments
Certain techniques are used to determine the intensities and magnitudes of defects and assist to find out their possible causes. Therefore suitable repair technique is specified accordingly. After applying repair weld non-destructive examination is also required to make sure that the defects have been completely eliminated. Specific NDT technique is selected and acceptance criteria is defined according to the job requirements. Moreover some terminal techniques are also required after post-treatments to check the complete removal of defects.
Welder must be qualified for the repair job and should have previous work experience. As it is stated earlier that repair work mostly involves hand operated procedure. A welder must be cautious during depositing the weld and prevent serious problems of distortion and unwanted stresses. Management staff only allow the authorized welder for the repair work.
Cleaning of repair portion
Before repair it is recommended to ensure the removal of coating, paint, and oil/grease from the section where the weld repair is to apply. Various pre-cleaning techniques are used for this purpose so that the required surface is prepared and defects free results are achieved.
People in inspection circle have an essential role in evaluation and estimation of weld quality throughout the procedure. During production an Inspector or NDT personnel ensures the quality of weld according to the quality plan. If the defect is detected during visual inspection then analysis and assessment lead the inspector to approve repair weld and after that inspection and non-destructive examination may also require after excavation process, repair weld and even after final treatment like post weld heat treatment.
In case of service repair weld, failure analysis is carried out to find the reasons for deviating the performance of an item.