Identifying which steel was used in a plate boat construction

[GoneDiving]

I'm about to go and look at some steel trawlers, both converted ex commercial units and some "custom" plan built private vessels.

I'd expect the ex commercial units to be constructed from the correct marine grade steels. However, how can I easily check if one off builds did not cheap out and build from standard cold rolled?

Is there an easy way to check? Are wear, pitting, corrosion patterns different between the two steel types?

Thanks

 

[KnotYet]

If you can find out where your candidates were built the yard will be able to tell you.
My main concern after checking the construction quality would be the how well it was
epoxied after construction.
After that I would check out the accessibility of areas behind the interior furniture, etc.

 

[DavidM]

Any large industrial area will have metallurgical testing specialists who can determine if the proper grade of steel was used. It may not be cheap though.

David

 

[O C Diver]

There is a hand held device that determines the alloys in metal. I don't remember the name of it. The scrap yard that my buddy works at has one. You put the device against the metal and through a light refraction mechanism, it analyzes the content. You have to be shooting at bare clean metal to get the analysis. I think the device was around $10k, but quite valuable when buying and selling metals.

If you get to a point of having the vessel surveyed, I would imagine a surveyor specializing in metal boats might have one or know where one could be rented.

Ted

 

[GoneDiving]

Thanks guys. I guess the ends can also justify the means. If a 30+ year old vessel is rust free, it's a good indication that the base metal, coatings and care were all done properly. Something peppered with holes will be avoided regardless of tech specs.

 

[RonR]

PMI test is what its called(Positive Material Identification) testing is the analysis of materials to determine the chemical composition of a metal or alloy at particular (usually multiple) steps of alloy manufacturing or in-process alloy installation.

But on that note, what do you consider a marine grade carbon metal? A36 AH36, DH36, and EH36? Know what you think it should be before paying for the test.

Most are just simple A36 or standard steel. a AH36 or DH or HE36 all have added Chrome or Mag and are slightly better in wet conditions. There are 100's of different carbon steels, know what you want before going further as most are just A36.

 

[woolf]

Some high quality custom boats come with a hull or builder's certificate, stating material used, and rules followed. Some yards are approved for metal building by classification bodies. That could be a start for further investigation.