STEEL HULLS with Composite Superstructure / Topsides

I owed a high pressure certified ASME fabrication plant.
What your doing with pre heating, is bring the steel up to temp
Your are experiencing is the differential of the temp of steel
to the humidity in the air.
There are good marine paints. I would recommend soda blasting
Before painting. Galvanizing 90mils is a good option.

 

Good question. Maybe there are microscopic voids on the surface. Clearly it must be held within a very thin lamina. I am not sure if any carbon crystals exist as discrete units within steel but if so it could absorb water. Just a discussion at this point in time but something to keep in mind when coating.

 

Heat treating steel requires an inert gas atmosphere, oil bath or mechanical barrier applied to metal to prevent surface burn oxidation caused by combination of air borne oxygen & water molecules.
Fire or forge welding metals requires the surface to be completely coated to prevent burning but if you heat a bar of steel to bright red or white heat then lay it on anvil with wetted surface the instant steam will blow scale of the steel. If water were trapped in the steel it would self destruct during the heat up.

Ask any hot dip galvanize plant worker what happens if you drop a piece of wet steel into a hot dip galvanized bath. The liquid 660C zinc will explode upwards driven by instant steam. If steel could contain even the most minute amounts of moisture it would burst explode when submerged in hot zinc killing anyone with 20m of the bath.

 

This does not explain why water will drip off a large section of steel when heated to moderate temperatures. This is not heat treatment nor can it be condensation. I will investigate this further to gain a better understanding. I trust the tradesman.

 

Anecdotal tales and poor conclusions from observation don't add up to materials science.

If there was a lot of water forming on the steel as it was heated then it was coming from somewhere else and most likely the heat source itself, condensing on the plate which wasn't hot enough yet to evaporate the condesate.

Similar to the water pouring out of your automobile exhaust when it's cold. Or did you think that was water that had soaked into the engine block and pistons

Steel can't absorb water. If you absorb that as a fact you'll be able to work out whats going on when it appears that it has.

 

I've seen a moisture halo around the application of LP gas flame to plating before , I think it was a product of the flame/fuel/air burn itself.
Jeff.

 

Materials science: great, so show evidence in compliance with the scientific method. I prefer to keep an open mind on such matters until proved otherwise beyond reasonable doubt. Its called caution. The relative point here relates to the desirability or otherwise of heating steel then allowing it to cool before applying primers.

 

Yes its most likely that it's actually water vapor in the gas or H2O forming from a combination of gasses .

 

The material properties of steel are already well researched and described very scientifically. Anyone can look up the material properties the hard work has been done and there's no need re-prove this.

I said before that Steel has a tightly packed lattice structure which has no room for water molecules. Therers a fundamental distinction here if we talk about material properties then they are the properties of the material in it's unadulterated form. Steel wool for example will trap and hold moisture. But steel as a material does not absorb any moisture. The distinction is important.

Are you suggesting that we suspend some very basic fundamental knowledge because someone eroneously thought the water was coming out of the steel plate ?

That's how urban myths start and I'm sorry but they have a nasty habit of spreading if they are not checked.

 

2 pieces of evidence implying that steel does indeed absorb water to a degree and hence the desirability of pre heating to reduce humidity.

Scientific paper:
Penetration of tritium (as tritiated water vapour) into low carbon steel and remediation using abrasive cleaning.
Lewis A, Warwick PE, Croudace IW.
Source
Solid Waste Department, UKAEA Winfrith Site, Winfrith Newburgh, Dorchester, Dorset DT2 8WG, UK.
Abstract
The UKAEA Winfrith site is in a phase of accelerated decommissioning and de-licensing which will generate significant volumes of metal wastes some of which may be suitable for disposal as exempt wastes. If contamination is present, it is often confined within the surface layers of the metal. The UKAEA Winfrith site operates a shot-blast facility (WACM) that removes paint and surface contamination from low carbon steel enabling surface contaminated painted metal to be processed and therefore certified as exempt. A study was conducted to determine whether tritium (as tritiated water vapour) has penetrated into the metal to levels exceeding the Radioactive Substances Act (1993), Substances of Low Activity (SoLA) Exemption Order criteria, and whether processing via the WACM removes sufficient tritium contamination that the SoLA Exemption Order criteria can be met. The results of sampling and analysis show that the tritium is mainly held in the paint or outer 40 microm layer of the metal and that processing through the WACM removes these layers along with sufficient tritium to meet the SoLA Exemption Order criteria.



This from a steel coating company:

While applying heat to the profile, the humidity is to be removed and the steel must be pre-heated at appropriate temperature. In order to acquire appropriate drying, before applying the primer onto the surface of the steel, the recommended steel temperature should be between 30 °C and 40 ° C depending on the primer type and thickness.

 

Please get down off you academic hobby horse. You are not the only one with a science degree here. I have not been dogmatic about anything. I have never said can't doesn't won't. My endeavour is enquiry as I want to know truth. I want to establish sound techniques for steel coating application, not how the size of my willy compares.

 

That's due to Surface roughness and irregularity not due to the fundamental material properties. And heating plate removes SURFACE moisture which could certainly help with some coatings in some circumstances.

I'm sorry if you take offence at being corrected but this is a forum, and everyone learns. Steel properties are not unknown. I said before (twice) it can only absorb water if it is manufactured with porosity, that includes cracks crevices voids and yes surface roughness.

 

Steel is not homogenous and therefore will most probably absorb substances to a degree. As steel surface will have microscopic voids and cracks. The above paper quite clearly states water vapour penetrated to 40 micron. The question is not if but rather how much. It may be on a micron scale. BUT do I have to repeat again?: this is about preheating/drying before coating and corrosion beneath a coating What is the motivation behind your posts? If it is just to partake in a war of words, then be my guest. You will lose.

 

Your goal posts seem to have moved ! So once again …..

I've been trying to help your understanding of material properties based on someone else’s anecdote ( the welder you quoted). Against this position you hold is a tome of materials property testing by metallurgists and chemists that don’t agree with your surmise. This is your position which is clear enough:

Polyurea holds moisture, steel wool holds moisture, steel as a homogenous engineering material doesn’t. That’s an important distinction.


Now I’ve said several times it can only absorb water if its manufactured with porosity that includes cracks crevices and surface roughness that can hold water molecules. But surface roughness only traps minute insignificant amounts of water molecules if you wet the plate you have a completely different scenario. That's where heating can dry it out but it's not required for plate that has a dry surface.

If you are interested :

Some modern surface tolerant epoxy undercoats can cope with quite a moist surface and high humidity levels. But the real reason for heating steel prior to painting is the dew point. Heating steel evaporates surface moisture AND stops condensation in humid conditions when the steel temp is below the dew point.

It’s always a pity when someone sees a forum discussion as a personal attack, that’s not how it’s meant, it’s a discussion. I’m sorry if it offends you but you were quite misinformed.
Even your welder would have realized that had such a large amount of moisture been in any steel the hydrogen embrittlement of welds would have been astronomical and the welds so porous they would have looked like swiss cheese.

Several people tried to tell you that it was obviously wrong just from simple observation , I’m telling you that you were wrong from basic material properties data. If you want to take umbrage that’s your prerogative but insults are not acceptable here .

 

I am telling you that you are wrong from basic material data. I can quote a number of research papers which deal with the formation of voids in steel when it is strained (e.g. in plate rolling). These form around inclusions at very low tensile deformation. e.g. a hull plate which is bent. The propagation of these voids is part of the failure process (cracking). There is also a natural surface process called decarburization which I suspect increases the near-surface porosity.

Steel texture is not a lattice (lattice refers to crystalline texture) but rather granular. Steel is a mixture, not a compound. I can post microscopic images and evidence on what I am hypothesising. But frankly I cannot be bothered.

Your posts have come across as condescending and arrogant. Why? because you assumed I was some Kiwi country hick from some greasy workshop? I could puff my chest out and quote my qualifications too. Why bother. I am interested in the subject of coatings on steel only. All my research to date suggests that anyone applying the first coat to steel should seriously consider drying it with heat before applying. That is all I have to say on the matter and the sole purpose of my posts. Adios