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Plastic coated hull


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17 minutes ago, Tony Brooks said:

Wasn't it some specific form of corrosion?

We used to supply Stainless steel cable fixing for offshore use, when attached to the Zinc coated steel cable tray there was huge problems with crevice corrosion in the splash-zone caused by a combination of water and two dissimilar steels.

We had to plastic coat the fixings using a polyester coating called Macropol, this solved the problem.

Our main competitor used Nylon 11 or Nylon 12 as their coating but this material is extremely flammable and actually contributes to the spread of fire (HB rated) so they were not allowed to use it. Did our sales a 'power of good'

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2 hours ago, WotEver said:

Yes, I think so... or fatigue. 

 

IIRC stainless steel is much more brittle than mild steel, so prone to cracking when subject to vibration and hard knocks.

 

Hence no good for a boat with a vintage 2 cylinder engine driven by Timothy West. ??

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3 hours ago, WotEver said:

I recall someone asking here once if anyone had ever made a SS narrowboat and iirc besides the cost aspect, there were some technical issues with the idea. I can’t recall what though. 

I'm sure I remember seeing some photos of a stainless steel narrowboat some years ago, IIRC the owner worked in the steel industry and got the materials cheap (but still pretty expensive compared to mild steel). Anyone else remember this?

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Welding heavy weight stainless can leave a lot of residual stress in the weld / heat affected zone and some stainless steels are prone to stress corrosion cracking. Not sure if this could be the issue.

 

Re the brittleness point above, that applies to the ferritic stainless steels, the 400 series, the 300 series austenitic alloys are not prone to brittleness.

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On 13/06/2020 at 16:50, BrandyMark said:

Hi Mike, Just reading through the brochure for the boat and it states PolyHotCote thermal spray powder so you are right. My little knowledge of power coating was that the components were placed in a oven after spraying, a big oven required for 20 tons of narrowboat! Was done 9 years ago, be interesting to know at what cost and what condition its in now. When I started this post, I was kind of hoping that the person who had it surveyed might be a member of this forum and would comment.

 

On 13/06/2020 at 17:02, Mike Tee said:

I don’t think it is powder coating, rather a solid (ie plastic) passed through a flame or high temp device to turn it to liquid and sprayed on. Then no further heating required. I’m intrigued as to how it can be repaired after damage.

To understand if PHC works, you need to find out what 'plastic' it is. If it is plastic, then it is not a thermoset resin like epoxy. I am not aware of anyone perfecting a technique to hot spray a plastic onto steel to emulate the performance of an epoxy. It certainly will not be a polyolefin ie polyethylene or polypropylene unless modified with something to improve the adhesion. Maybe it is a nylon but that would be very expensive. The biggest problem when we were trying to develop coatings in the 80's was adhesion of any coating and that requires the coating to 'wet' the surface properly. Hot spraying doesnt do this very well. When you hot spray zinc, you are not looking for the best adhesion as the zinc works to passivate the surface (as red lead used to do).

If this techonolgy worked (PHC) then you would be hearing a lot more examples of it. I'd never heard of it in use.

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Going back into my memory from working in the 1980s, we could buy steel reactors that had been spray coated with PTFE, the steel surface was very rough and the PTFE was heat treated afterwards to ensure a good bond. I recall the salesman had samples of the coated steel about 2" x 6" that had been the coating mechanically separated from half of the plate to let you see if you could peel off the remaining half. Never could.

 

PTFE lining would be very immune to canal water (we carried out reactions with boiling concentrated hydrochloric acid in it) and when entering a tight lock, you would just glide in.

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It took a while, but I don't have a great deal else to do in the present situation!!

http://www.tecnosupply.com/en/coating-and-blasting/materials/thermoplastic-powders-for-anticorrosion-protection/phc-a-phc-ah

Don't really understand too much of the technical stuff, but might be of interest to anybody following this subject

 

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42 minutes ago, Mike Tee said:

It took a while, but I don't have a great deal else to do in the present situation!!

http://www.tecnosupply.com/en/coating-and-blasting/materials/thermoplastic-powders-for-anticorrosion-protection/phc-a-phc-ah

Don't really understand too much of the technical stuff, but might be of interest to anybody following this subject

 

Can you download any of the linked technical files? The page you linked to says nothing and it says error when I try and download any of the tech stuff.

 

1 hour ago, PeterF said:

Going back into my memory from working in the 1980s, we could buy steel reactors that had been spray coated with PTFE, the steel surface was very rough and the PTFE was heat treated afterwards to ensure a good bond. I recall the salesman had samples of the coated steel about 2" x 6" that had been the coating mechanically separated from half of the plate to let you see if you could peel off the remaining half. Never could.

 

PTFE lining would be very immune to canal water (we carried out reactions with boiling concentrated hydrochloric acid in it) and when entering a tight lock, you would just glide in.

PTFE is one of the few 'plastics' that will stick very well to steel (it has Flourine molecules in it which makes strong bonds to steel) but it would be too expensive to coat a boat and I dont think can be hot sprayed.

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I didn't mention the name of the plastic covered boat in question and I know some already were aware but, because it as now been sold and if anyone would like a quick look before it taken of site, the boat name is Scythia listed by ABNB. She is a lovely looking S M Hudson 57tf built in 2000 listed for £65k. Someone has a very nice boat regardless of the plastic coated hull.

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