Welding and Smelting Inspection (Engineer)?
Welding and smelting are very different activities. Although (critical/structural) welds might be inspected, I can't think what 'inspection' would take place for smelting - it would be the resulting castings which might be inspected for quality, and that would probaby be a "casting inspector".
I'd lean towards the possibility of "Water and Sanitary Inspect(or) (Engineering)".
'Sanitary Inspector' was a formal and statutory occupation, roughly equating to the modern environmental health officer.
When Local Authorities were responsible for the supply of clean water and the provision of sewerage this may have come under the domain of the 'Chief Sanitary Inspector'. The functions of this department would have included both the infrastructure (engineering) and quality/'wholesomeness'. The latter is what evolved into Environmental Health.
So I think it is plausible someone would describe themselves as a "Water and Sanitary Inspector (Engineering)"... but I have absolutely no proof of this, other than past experience working in a drainage department where such words regularly cropped up in the historic records.