IMPORTANCE OF GOOD QUALITY WELDS IN TRAILERS

The topic of discussion today is one aspect of structural fabrication i.e welding to which the transporters do not give much importance to.  The general feeling in transporters is that welding is essential but it is  only as an ornamental requirement and does not deserve much skill and attention. This kind of mind-set is prevalent and shared by most of the transporters.  However it must be noted that the stability and the strength of the structure totally depends on the quality of the welds.

This aspect need not be discussed where both the parties i.e the manufacturer and the customer have a sound engineering background.  The problem arises where one of the parties does not have a sound engineering background and cannot appreciate the topic of discussion.

Let us understand what happens when a welding joint in a trailer or a semi trailer fails. 

1. It can lead to serious accidents.
2. It can cause distortion of structure and lead to unnecessary maintenance.
3. Tyre wear and tear.
4. Increase in down time of a productive vehicle.

The following pictures are classic example of inadequate welding and welding failure.

The  picture on the left shows a structural joint in which there is incomplete and poor quality of weld.  The picture on the right shows a failure of a weld joint due to a defect called as lack of fusion.  In this case the welder has failed to fuse the parent metals while depositing the filler material.  This type of defect shown in the picture is probably because of  low current setting coupled with inadequate skill of the welder.

The adjoining picture is a classic example of good fillet weld joint.












So in order to avoid failure and breakdown due to defective welding the following should be insisted upon.  The job of fabrication of a trailer body/frame is nothing short of structural fabrication and all the requirements relevant to fabrication and welding codes as per ASME should be insisted upon.  The following are the basic documents that the client should insist upon.

1. Material test reports for physical testing and chemical analysis  conforming to ST-42 or any other equivalent standard should be insisted upon. It is important to understand that while freezing a standard for the material to be used, the end application has to be kept in mind.
   
   
2. Once the materials to be used are tested and found satisfactory, the next step will be to establish a welding procedure.  There are standard formats in ASME sec IX which clearly define the parameters that have to be recorded. This procedure qualification has to be witnessed by an  welding inspector.  This process is called as establishing a “PQR”, the full form is “Procedure Qualification Record”.By carrying out this exercise we achieve the following. The material suitability of  the welding electrodes and the parent metal used in the structure is tested for physical and chemical properties.  The position of the weld joint and the welders skill in that position is both tested.  There are other intricate parameters which are also established like welding process, size of electrode, current, voltage, flow of gas in case of MIG/TIG, surface preparation, geometry of the weld joint, cleaning processes etc. The test sample of the welded material is sent to approved laboratories for non destructive and destructive testing as per relevant codes.
   
   
3. The next step is qualification of welders as per the established PQR and this process is called “WPS”.......

(To be continued……)

JAGDISH S KOLUR

Partner - BELCO ENGINEERS

Telefax: +91-22-27423841

Mobile:  +91-9819076201

E-Mail:  jagdish@belcoengineers.com