I work for a company that builds mobile power substations that are built onto a heavy haul trailer. Our normal spec to the trailer manufacturer calls for all joints to be welded completely with no stops. This applies to every joint on the trailer wether it is necessary or not. The purpose of this spec is to prevent corrosion. We have recently used a new manufacurer who does not want to comply with the spec, claiming that certain joints are left unwelded to allow the trailer to flex without cracking welds. This explanation does make sense to me, but I am not an engineer, and I am not familiar with any trailer code (if there is one out there). The problem is that the two trailer manufacturers are in conflict about wether or not this is an issue. It seems to me that without allowing flex the welds will crack eventually, wich will rust, and the cracks will most likely propagate into a worse situation than leaving the areas unwelded in the first place. Does anyone out there have an answer?

Mac

Built trailers for years myself................. if you weld across the rail you stymie the motion of the ocean and will have a broken frame rail,always weld with the rail never across it.I'd buy a trailer from the outfit that won't weld across the rail myself,as they are right and your drawing is wrong.

You did not say whether your employer designed the heavy hauler and provided the approved drawings to the fabricator or if the fabricator is responsible for designing t heavy hauler to meet criteria established by your employer.  

There are two completely different situations that result in different responses.

If your employer provided the fabricator with a set of design drawings the fabricator has an obligation to construct the heavy hauler per the approved drawings. Any deviation is a noncompliance unless your employer gives them permission to change the design.

If your employer provided the fabricator specific criteria and the fabricator has the responsibility to design and construct the heavy hauler, then the fabricator can pretty must do as they wish as long as the criteria is met.

If the latter is the case, I would expect your employer to have an opportunity to review the proposed design before giving the fabricator the "go ahead" to begin construction. If your employer didn't review the design, shame on your employer.

Over the road vehicles are subject to fatigue. The designer must factor in conditions like changes in thickness, changes in width, sharp corners, or changes in geometry that tend to concentrate stresses and promote fatigue failure. Companies that have a long history of building heavy haul trailers usually have plenty of experience designing with fatigue in mind. They know what does and what doesn't work. I would consider the fabricator's history as part of the selection process.

Whichever scenario fits your situation, the fabricator has an obligation to construct the heavy hauler in accordance with the approved design drawings regardless of who actually designed it.

Best regards - Al

seems as if corrosion was such a problem where you are they would specify the trailers be hot dip galvanized?

Thanks everyone for your input. It turns out that Al is correct. We only provided the manufacturer with a set of specs and they were responsible for the design/build. In the design review with our engineers the areas that were left unwelded was accidentally overlooked. For all future jobs the manufacturer has reluctantly decided to meet our spec and weld every joint completely.