New boat steel question

[Chris Williams]

3 minutes ago, The dog lady said:

Have been looking at a boat builder who says they shot-blast new hulls before epoxy blacking to remove 'mill scale' -  a type of iron oxide which is formed during hot rolling process - which would otherwise eventually flake off taking top coatings with it and allowing pitting and corrosion. Is this common practice?

I would think it depends if they are a proper boat builder or a cowboy outfit that uses any old bit of metal from the local scrappie.

[The dog lady]

Hmm.....just found posts on here from 2014 about this particular builder. Nightmare stories by everyone who dealt with them. 'High-end' bespoke builder too. 

[Chris Williams]

1 hour ago, The dog lady said:

Hmm.....just found posts on here from 2014 about this particular builder. Nightmare stories by everyone who dealt with them. 'High-end' bespoke builder too. 

Yes, Talk to the man who has got one.  Old car advertisement.  Sound advice.

[Iain_S]

2 hours ago, The dog lady said:

Have been looking at a boat builder who says they shot-blast new hulls before epoxy blacking to remove 'mill scale' -  a type of iron oxide which is formed during hot rolling process - which would otherwise eventually flake off taking top coatings with it and allowing pitting and corrosion. Is this common practice?

I suspect not as common as it should be ?

[Alan de Enfield]

1 minute ago, Iain_S said:

I suspect not as common as it should be ?

I thought that anyone using epoxy had to shot-blast the hull to get adhesion.

 

It is rarely (if ever) done for standard 'blacking'.

[ditchcrawler]

Not a steel expert by any means but dont a lot of the better builders use blasted and primed steel or is that a load of old whats name?

[WotEver]

24 minutes ago, ditchcrawler said:

Not a steel expert by any means but dont a lot of the better builders use blasted and primed steel or is that a load of old whats name?

It wouldn’t appear so from the many stories we hear about 2 year old boats with huge areas of bare steel on the hull where the mill scale has let go. 

[cuthound]

Not common practice, but very good practice. Shotblasting and epoxy blacking is much more expensive than juzt slapping a couple pf coats of bitumin on.

 

Epoxy lasts longer and requires less frequent docking, perhaps every 5 years I stead of every two.

 

My boat was epoxy blacked from new and is beIng redone this year at 12 years old, having had a repair and touch up when I bought it at 6 years old.

 

[dmr]

On 06/04/2019 at 19:53, Mad Harold said:

I will try.    Narrowboat hulls don't corrode evenly all over,they start with pitting of the surface.If there are only a few pits,they can be spot welded,but if deep pits have spread over a large area then overplating or cutting out the corroded area and welding in new steel will be required.

Now,why do these pits start in the first place? why doesn't the steel corrode evenly?

My theory.  When steel is made iron ore,limestone and other ingredients that I don't know about are all melted together,and air is blasted through to get rid of the unwanted stuff (slag) and if this process is not done properly and slag is left in the steel to save a few quid,then that I think is where the rust pits will start.

It is just a theory,and am quite prepared for incoming because I don't have any qualifications in metallurgy,but I have seen steel being cut up with a torch for scrap.(my first wife's father had an industrial scrap business) and some steel cut like butter,and other stuff,there was sparks flying all over the place and was difficult to cut.

 

This makes sense to me.

 

I have drilled quite a few holes in my boat (not the baseplate I must add ) and over my life time have drilled a lot of holes in steel and have often felt I go through hard, soft and crunchy bits. Only last week I was drilling some holes in the boat and after a couple of easy ones the drill bit suddenly jumped and snapped, and I know it was a really good bit because I got a whole packet of them for £3 at Screwfix.

 

................Dave

 

[Guest]

1 hour ago, cuthound said:

Not common practice, but very good practice. Shotblasting and epoxy blacking is much more expensive than juzt slapping a couple pf coats of bitumin on.

 

Epoxy lasts longer and requires less frequent docking, perhaps every 5 years I stead of every two.

 

My boat was epoxy blacked from new and is beIng redone this year at 12 years old, having had a repair and touch up when I bought it at 6 years old.

 

My findings too. I much prefer epoxy. It pays for itself in my experience.

3 hours ago, ditchcrawler said:

Not a steel expert by any means but dont a lot of the better builders use blasted and primed steel or is that a load of old whats name?

Our shell was blasted when new 15 years ago. I watched them do it. Certainly no probs. with mill scale!

[yabasayo]

   On 06/04/2019 at 19:53,  Mad Harold said: 

I will try.    Narrowboat hulls don't corrode evenly all over,they start with pitting of the surface.If there are only a few pits,they can be spot welded,but if deep pits have spread over a large area then overplating or cutting out the corroded area and welding in new steel will be required.

Now,why do these pits start in the first place? why doesn't the steel corrode evenly?

My theory.  When steel is made iron ore,limestone and other ingredients that I don't know about are all melted together,and air is blasted through to get rid of the unwanted stuff (slag) and if this process is not done properly and slag is left in the steel to save a few quid,then that I think is where the rust pits will start.

It is just a theory,and am quite prepared for incoming because I don't have any qualifications in metallurgy,but I have seen steel being cut up with a torch for scrap.(my first wife's father had an industrial scrap business) and some steel cut like butter,and other stuff,there was sparks flying all over the place and was difficult to cut.

 

This makes sense to me.

 

I have drilled quite a few holes in my boat (not the baseplate I must add ) and over my life time have drilled a lot of holes in steel and have often felt I go through hard, soft and crunchy bits. Only last week I was drilling some holes in the boat and after a couple of easy ones the drill bit suddenly jumped and snapped, and I know it was a really good bit because I got a whole packet of them for £3 at Screwfix.

 

................Dave

 

Both above correct in my view. That's why you should have a certificate of origin and quality for steel supplied for a new boat build. See thread on Steel quality and origin in build blog. 

 

Edited April 11, 2019 by yabasayo
spelling as usual