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.
Post treatment
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.
Competent welder
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.
Inspection Staff
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.