Steel quality and origin

[yabasayo]

Having recently seen a 12 year old boat that needs replating of bottom and sides, I wonder why steel quality doesn't seem to feature anywhere, least of all in the builders sales blurb.

There are many different grades of steel plate and different quality standards within each grade. For example some cheaper steel originating in the Far East has been found to contain inclusions that significantly accelerate corrosion. On the other hand Corten steel can exhibit markedly improved corrosion resistance compared with other mild steels although it is more expensive. What measures are taken to ensure that the welding material is compatible with the structural steel itself, in order amongst other things to reduce dissimilar metals corrosion between the weld and the structural steel ? Does the steel comply with EN10204 3.1 and if so, where is the certification ? Are the welders appropriately qualified and how is this demonstrated ?

I had a chat with one well known shell fabricator a few weeks ago and asked some of the above questions. The answer - "Steel's all the same, don't worry about it. We know what we're doing with the welding."

If you are going to invest £100k or thereabouts in a new boat, surely the quality and potential longevity of the hull is as important as the fit out, if not more so.

I have attached a very informative (at least I thought so )presentation for interest.

Introduction-to-iron-and-steel-testing-ferrous-corrosion-and-cathodic-protection.pptx

[zenataomm]

Steel's all the same, don't worry about it.

[MtB]

14 minutes ago, yabasayo said:

Having recently seen a 12 year old boat that needs replating of bottom and sides, I wonder why steel quality doesn't seem to feature anywhere, least of all in the builders sales blurb.

There are many different grades of steel plate and different quality standards within each grade. For example some cheaper steel originating in the Far East has been found to contain inclusions that significantly accelerate corrosion. On the other hand Corten steel can exhibit markedly improved corrosion resistance compared with other mild steels although it is more expensive.

 

 

 

What grade of steel was it made from? It might have been Corten steel anyway...

 

 

 

 

 

[Chewbacka]

Welder qualifications?  Easy, put the boat in the water if it leaks he/she isn’t 

[Boater Sam]

I used to employ an engineer who had been at Shotton steel works for many years.

He was certain that British Steel never rolled 10mm mild steel plate. If so where did/does it come from?

BS EN 10 025 is standard mild steel.

 

[Captain Pegg]

57 minutes ago, yabasayo said:

Having recently seen a 12 year old boat that needs replating of bottom and sides, I wonder why steel quality doesn't seem to feature anywhere, least of all in the builders sales blurb.

There are many different grades of steel plate and different quality standards within each grade. For example some cheaper steel originating in the Far East has been found to contain inclusions that significantly accelerate corrosion. On the other hand Corten steel can exhibit markedly improved corrosion resistance compared with other mild steels although it is more expensive. What measures are taken to ensure that the welding material is compatible with the structural steel itself, in order amongst other things to reduce dissimilar metals corrosion between the weld and the structural steel ? Does the steel comply with EN10204 3.1 and if so, where is the certification ? Are the welders appropriately qualified and how is this demonstrated ?

I had a chat with one well known shell fabricator a few weeks ago and asked some of the above questions. The answer - "Steel's all the same, don't worry about it. We know what we're doing with the welding."

If you are going to invest £100k or thereabouts in a new boat, surely the quality and potential longevity of the hull is as important as the fit out, if not more so.

I have attached a very informative (at least I thought so )presentation for interest.

Introduction-to-iron-and-steel-testing-ferrous-corrosion-and-cathodic-protection.pptx

I fear you have linked to a paper from the internet that was written by a man who did his research on the internet. Note he is a marine surveyor and not a metallurgist or engineer.

 

Much of what he writes isn't relevant to the subject at hand in any case and on first reading seems a little contradictory in itself. I think a fair bit of his steel making history is misguided. Not that it's particularly relevant since the main problem with these debates regarding narrowboats is that nearly all the properties of steel that matter to the metallurgist or engineer aren't relevant to narrowboats.

 

All you need is something that has high fracture toughness and is relatively easy to fabricate and that is why almost all steel boats are built with ordinary grade S275 (43A) steel. That's basic mild steel of the sort that forms the vast majority of worldwide steel usage irrespective that are many other grades and alloys available. It will be more stressed as a result of the locked in forces caused by rolling and straightening than it ever will be by the exertions of cruising the inland waterways. You simply don't need a higher grade and weathering steels have nothing to do with anything in the context of boats.

 

Steel is produced to very consistent standards to the same quality assurance certification around the world as it is a globally traded commodity. Most of what I see and hear in respect of the supposed superior quality of older steel and horror stories concerning imported steel is completely counter to my own professional knowledge and experience or that of the metallurgists I work with who are experts in their field (and that's industry not academia).

 

The design of the shell and the preparation and welding are far more relevant than the steel itself but if longevity is your principal concern you need to think about the environment you keep your boat in, and how you are going to protect and maintain your hull.

 

JP

 

 

 

[Captain Pegg]

1 minute ago, Boater Sam said:

I used to employ an engineer who had been at Shotton steel works for many years.

He was certain that British Steel never rolled 10mm mild steel plate. If so where did/does it come from?

BS EN 10 025 is standard mild steel.

 

Not all mills would necessarily roll all products. 10mm is a standard plate size. BS EN 10025 is a technical specification for hot rolled products. Mild steel refers to a group of steels of which the basic product is S275 (or Grade 43A in old BS4360 speak). Other mild steel grades are available.

 

JP

[AMModels]

BS did roll 10mm steel, Corby for one produced lots of it....it wasnt very good but it was definitely, nominally, 10mm.  What surprises me about boat builders is they dont use pickled steel, no scale ready to take paint straight from the off, easier to clean should corrosion occur in the building phase. 

 

[yabasayo]

1 hour ago, Captain Pegg said:

I fear you have linked to a paper from the internet that was written by a man who did his research on the internet. Note he is a marine surveyor and not a metallurgist or engineer.

 

Much of what he writes isn't relevant to the subject at hand in any case and on first reading seems a little contradictory in itself. I think a fair bit of his steel making history is misguided. Not that it's particularly relevant since the main problem with these debates regarding narrowboats is that nearly all the properties of steel that matter to the metallurgist or engineer aren't relevant to narrowboats.

 

All you need is something that has high fracture toughness and is relatively easy to fabricate and that is why almost all steel boats are built with ordinary grade S275 (43A) steel. That's basic mild steel of the sort that forms the vast majority of worldwide steel usage irrespective that are many other grades and alloys available. It will be more stressed as a result of the locked in forces caused by rolling and straightening than it ever will be by the exertions of cruising the inland waterways. You simply don't need a higher grade and weathering steels have nothing to do with anything in the context of boats.

 

Steel is produced to very consistent standards to the same quality assurance certification around the world as it is a globally traded commodity. Most of what I see and hear in respect of the supposed superior quality of older steel and horror stories concerning imported steel is completely counter to my own professional knowledge and experience or that of the metallurgists I work with who are experts in their field (and that's industry not academia).

 

The design of the shell and the preparation and welding are far more relevant than the steel itself but if longevity is your principal concern you need to think about the environment you keep your boat in, and how you are going to protect and maintain your hull.

 

JP

 

 

 

The 'man' concerned is a very experienced surveyor and a professional engineer (as am I). He does not claim to be a metallurgist.

Steel is certainly not produced to the same quality standard around the world as you claim. Both the Chinese and Indian governments have recently launched programmes to try to improve the quality of some of their steel produced which has been previously been made from low grade iron ore, non certified alloys (scrap), bulking agents and additional elements such as Boron. Scale and slag inclusions in rolled plate have also been common. There is an established record of structural failure and accelerated corrosion in the offshore and shipping industries associated with sub standard steel. I personally would avoid a boat built with cheap steel of unknown origin.

If you mean by 'higher grade' higher tensile strength, I agree thats the last thing you need in a pleasure boat as it's expensive and is prone to cracking. However I was referring to quality, not strength as such. Corten steel does have better corrosion resistance.

I agree also that the welding quality is important as I mentioned in my original post.

Edited October 5, 2018 by yabasayo

[DandV]

Does Corten have superior corrosion resistance in submerged applications? I am far from convinced.

[Captain Pegg]

1 hour ago, yabasayo said:

The 'man' concerned is a very experienced surveyor and a professional engineer (as am I). He does not claim to be a metallurgist.

Steel is certainly not produced to the same quality standard around the world as you claim. Both the Chinese and Indian governments have recently launched programmes to try to improve the quality of some of their steel produced which has been previously been made from low grade iron ore, non certified alloys (scrap), bulking agents and additional elements such as Boron. Scale and slag inclusions in rolled plate have also been common. There is an established record of structural failure and accelerated corrosion in the offshore and shipping industries associated with sub standard steel. I personally would avoid a boat built with cheap steel of unknown origin.

If you mean by 'higher grade' higher tensile strength, I agree thats the last thing you need in a pleasure boat as it's expensive and is prone to cracking. However I was referring to quality, not strength as such. Corten steel does have better corrosion resistance.

I agree also that the welding quality is important as I mentioned in my original post.

I think some caution is required with scare stories about imported steel. 30 years ago there were similar stories regarding European steel as you hear today with Asian steel. There is a degree of protection of interests involved. I base my comments on speaking with professionals who are now experts in my industry and have previously worked as consultants in the quality assurance of steelmaking, in research developing new alloys, as shopfloor technicians in steel mills, as welders and as non-destructive testers. All of that is relevant to my daily work and I rely on these folk to do my work, part of which requires me to have a working knowledge of specialist steels in respect of their specification, testing and performance. Something I have been involved with for over 25 years although I consider myself a generalist and not an expert.

 

Note that I didn't say steel is produced to the same quality standard worldwide. I said it is produced to a very consistent standard and to the same QA certification.

 

There is a history of failure due to specific flaws in steel in my industry too and that involves steels of which the vast majority were produced in UK mills. That doesn't mean that UK steel is cheap rubbish though I could probably concoct a scare story to that effect from the collection of failed samples I have at my disposal if I wished. There also tends to be a lot of folklore associated with this sort of history so suspicions remain long after the causes have been eliminated.

 

Just picking up on a couple of points you make, do you realise that practically all (if not all) steel reinforcing bar made in the UK is made from scrap? That's the standard process for producing steel by the electric arc furnace method which is used by Celsa in Cardiff to provide the semi-finished product for their rod mill. Also steel converters in integrated iron and steel works are always charged with scrap prior to addition of the pig iron. The thing with steelmaking is that the whole process is all about refining a 'dirty' product be it molten scrap or pig iron into a tightly specified product. You can't buy steel that doesn't contain scrap but it doesn't make any difference to the finished product.

 

Higher grade steel is used in my world specifically to prevent fatigue cracking. Tensile strength isn't the sole issue in play but the general rule is that a higher strength material will exhibit more brittle failure, i.e. it will fail more suddenly, but that isn't the same thing as being more prone to cracking.

 

Weathering steels (of which Corten is a specific product)  generate their corrosion resistance by reaction of the surface with the atmosphere to form a specific protective oxide layer. There is no point using them underwater where they won't develop that layer or if you want to paint the steel.

 

I am interested in your assertion that there is history in shipbuilding and offshore of corrosion being linked to correct composition. I inspect steel of varying vintage and origin on a regular basis and I don't see any observable difference in the way it corrodes other than where specific catalysts are present. Is this a personal or second hand experience of yours?

 

JP

 

 

 

 

 

 

 

[Sir Nibble]

What do they make submarines out of?

[Chewbacka]

1 hour ago, Sir Nibble said:

What do they make submarines out of?

Good question, but submarines spend much of their life deep underwater where the oxygen levels are very low.  I would also think toughness is more important than corrosion resistance as you wouldn’t want it cracking every time a nearby depth charge goes bang.........

[Sir Nibble]

14 minutes ago, Chewbacka said:

Good question, but submarines spend much of their life deep underwater where the oxygen levels are very low.  I would also think toughness is more important than corrosion resistance as you wouldn’t want it cracking every time a nearby depth charge goes bang.........

I was thinking of exactly that, toughness. The cycling of compression and decompression of the pressure hull.

Edited October 6, 2018 by Sir Nibble

[MtB]

9 minutes ago, Sir Nibble said:

I was thinking of exactly that, toughness. The cycling of compression and decompression of the pressure hull.

 

I thought you were implying that if a submarine sinks, it doesn’t really matter does it?

[BEngo]

Submarines hulls are made of high strength high toughness steels.  The welders are somwhat special too.

Boats are generally not painted but are covered in rubbery tiles.

They also, like pressurised or miltary aeroplanes, have a hull life based on pressure cycles.

N

[Dr Bob]

14 minutes ago, BEngo said:

Submarines hulls are generally not painted but are covered in rubbery tiles.

 

....so they can bounce off the lock gates when they come up the GU.

[Bee]

Building narrowboat hulls is very competitive, profit margins are tight, they are not 'commercial' craft, just leisure things really, narrowboats are immensely strong and lives are not usually at stake, they are more than adequate for the job they are built for and the bit that we worry about - corrosion - is really up to us to address. Keep the inside surface dry and hopefully painted and the outside painted with proper paint and drag the thing out every 3 or 4 years and check it over and most problems will disappear.

[David Schweizer]

12 hours ago, zenataomm said:

Steel's all the same, don't worry about it.

I hope that was intended to be a joke. There are actually more than ten generic European Standards for steel , with something like seventy sub-catagories within those standards. Some will be more appropriate for boat building than others.

 

 

Edited October 6, 2018 by David Schweizer

[NB Esk]

Speaking as someone who has worked both new and old steels, I believe there is very much a difference.  For smaller jobs my method of choice in cutting steel would be the 41/2" angle grinder with 1mm cutting disc.  Using this on some new steels I'm fairly sure I can detect "hard" spots in the plate.  The blade travel slows and again, fairly sure, I can see a slight change in spark colour.

A few weeks ago I re used a plate from an eighty year old sea going tug (JUMSEY) with no such indication, almost a pleasure to work.

As regards weldability, over the last six months I've re done the baseplate welds on a Piper narrow boat and a wide beam of indeterminate make.  The Piper boat was again, almost a pleasure to work on.  The wide beam was a pain.  Same machine, same settings and same electrodes, the only difference was the steel.

 

 

 

[Captain Pegg]

29 minutes ago, David Schweizer said:

I hope that was intended to be a joke. There are actually more than ten generic European Standards for steel , with something like seventy sub-catagories within those standards. Some will be more appropriate for boat building than others.

 

 

Joke or not, in terms of narrowboat building it's accurate.

 

There is a massive difference between what technical standards exist, what is routinely manufactured, what is readily available to purchase and what is actually used. In terms of narrowboats it almost always boils down to one. There is good reason for that. There isn't really much need for this discussion.

 

JP

[zenataomm]

It's all crushed Cortinas

[system 4-50]

Where can I get the rubbery tiles?  If it saves having to paint I'm all for it.  Do they come in different colours?

[WotEver]

25 minutes ago, system 4-50 said:

Where can I get the rubbery tiles?  If it saves having to paint I'm all for it.  Do they come in different colours?

Don’t bother, they fall off...

www.popularmechanics.com/military/weapons/amp25578/the-navys-submarines-are-still-shedding-their-rubber-like-skins/

Edited October 6, 2018 by WotEver

[Dr Bob]

2 hours ago, system 4-50 said:

Where can I get the rubbery tiles?  If it saves having to paint I'm all for it.  Do they come in different colours?

 

1 hour ago, WotEver said:

Don’t bother, they fall off...

www.popularmechanics.com/military/weapons/amp25578/the-navys-submarines-are-still-shedding-their-rubber-like-skins/

....and they only cost £3000 each.