Welding Inspection Stages and What to look for during welding inspection

WELDING INSPECTION

 

Welding is one of the important activities being carried out during shipbuilding and ship repair. Much of the welding being done during shipbuilding or ship repair is done manually though there has been some amount of automation in welding being used in the industry. Reliability of a welded joint is important during shipbuilding and ship repair. Various standards and quality systems are available for ensuring a good quality welded joint. There are a number of factors that attribute to the quality of a weld joint, namely quality of the material being welded, selecting the correct electrodes, joint preparation, welder skill, welding parameters used, electrode quality, etc

Good quality weld joint can be achieved by carrying out inspection of the weld joint at various stages of carrying out the welding of the joint. Inspection indicates whether the prescribed standard of quality has been met. Visual inspection is the most economical Non Destructive Testing (NDT) but it must take place constantly, namely Before welding, during and after welding.

 

Weld joint inspection is carried out at the following stages:

·         Before welding

·         During welding.

·         After welding

What to look for during a welding inspection ?

Before Welding Inspection :

Type/state of base material - The material should be examined to see if they meet specifications for quality, type, size, cleanliness, and freedom from discontinuities. We may need to check the material certificate issued by the manufacturer for the chemical and mechanical properties duly endorsed by the material inspection agency which generally would be the classification society . Foreign matter, like grease, paint, oil, oxide film, heavy scale that should be detrimental to the weld shall be removed. The pieces to be joined should be checked for straightness, flatness, and dimensions. Warped, bent, improperly cut or damaged pieces should be ordered for repair or rejected.

 

Joint design & Joint Preparation - It has been observed that 50% of the weld quality can be achieved by a good edge preparation. A good joint design will provide access for the welder, adequate root opening to permit full fused penetration and correct groove angle to minimize volume of weld metal. The joint preparation must be correct before welding is started, not only to meet the specifications, but also to give assurance of weld quality.

 

Common faults to look for in Joint preparation :

·         Improperly cut edges.

·         Misalignment between the plates being joined.

·         Improper root gap and Groove angle. (Too small root gap may result in incomplete penetration and too wide root gap may result in melt through)

Welding process - Inspection before welding also includes verification of  correct process and procedures are to be employed - that the electrode type

and size and the equipment settings for voltage and amperage are as specified - and that provisions are made for required preheat or post

heat. Each welding process has its advantages and limitations, and each introduces problems affecting joint preparation, welding procedures and

operator training, hence due diligence needs to be taken in choosing the right welding process for the right kind of job.

 

Consumables - Select the right electrode for the right kind of job. Assistance may be taken by using the Manufacturers Product brochures in selecting the correct electrodes. Check at regular intervals that the consumables used match the required specifications. Also check for the proper storage of the consumables and proper manufacturers procedures are followed during its use.

Welding procedure - To ensure uniform results the welder's procedures must be spelled out in detail and followed rigorously during welding.

Welder's qualifications - Only qualified welders must be assigned to the welding jobs.

 

During welding inspection :

Compare welding parameters with procedure - Check that the welding parameters match the parameters laid down in the approved welding procedure.

Inspect each pass of welding before the next pass - When a weld joint comprises of more than one pass of welding it may be desirable to inspect each pass before the next based on the criticality of the joint and the application of the weld. The root pass in a multipass weld is the most critical one with regard to weld soundness and needs to be checked for quality deficiencies such as cracks, inadequate penetration, and gas and slag inclusions prior commencement of the next pass of welding.

 

After welding inspection :

Final visual inspection after welding - Visual inspection after welding is useful in evaluating quality, even if ultrasonic, radiographic, or other NDT methods are to be employed. As welding progresses, surface flaws such as cracks, porosity, and unfilled craters can be detected, leading to repairs or rejection of the work. There is no point in carrying out sophisticated inspection using NDT methods for an obvious bad weld. Dimensional variations from tolerances, warping, and faults in appearance are detected visually at this stage. Welds must be cleaned from slag to make inspection for surface flaws possible. A 10x magnifying glass is helpful in detecting fine cracks and other faults. Shot blasting should not be used prior to examination, since the peening action may seal fine cracks and make them invisible. The objective of visual inspection at this stage is not only to detect non permissible faults, but also to give clues as to what may be wrong in the entire repair /fabrication process. If the inspector has a sound knowledge of welding, he can read much from what he sees. Thus, the presence of excessive porosity and slag inclusions may be an indication of insufficient current even if the dial readings on the machine tell otherwise. Subsequent tests will also give clues to faults in equipment or procedures, but the information acquired through visual examination allows corrections to be made before results from more sophisticated methods become available.

 

Size of weld (measuring) - A welders gauge and Ruler may be used for determining the size and the length of welds for checking the welding with the design requirements. The extent and continuity of the weld, its size, and the length of segments in intermittent welds can be readily measured or recorded. Under welding is not acceptable as it compromises the strength of a weld and may not be suitable for its intended use. However over welding is also not desirable as it increases production costs and serves no useful purpose. Overwelding only makes the welding assembly stiffer and heavier and may increase the distortion in the weld assembly due to more heat input caused due to overwelding.


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