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Coal Tar Expoxy Performance

Coal Tar Expoxy Performance

Coal Tar Expoxy Performance

(OP)
Hey Guys, I'm new to the forum.

Currently I'm working on a project where they have a floating bridge with pontoons across a salt water river in Guyana. We're currently using CTE to coat the pontoons (Carbon Steel) and are getting about 4-5 years out of it before the corrosion gets really bad again. Can anyone tell me past experiences they had with CTE Lifetimes in a similar environment?

RE: Coal Tar Expoxy Performance

CTE Lifetimes? Past experience? They're now all dead of cancer or being killed at the protest rally....lol.

RE: Coal Tar Expoxy Performance

(OP)
Apparently Sherwin Williams is still willing to make CTEs though lol.

We've been using this coating for 20 odd years now, my country usually lets cancer off the hook.

Do you know of any other coatings which can yield the same price and performance and CTE though?

RE: Coal Tar Expoxy Performance

Sorry Andy, as far as I know nothing beats CTE as cost and acceptable performance. Obviously, there are other high tech coatings from glass flake to thermal spraying, but the cost can be an issue. However, the longevity could offset the initial cost, particularly with thermal spraying.

RE: Coal Tar Expoxy Performance

(OP)
Thanks Gr2. Thermal Spraying is out of the question for my application.. told my boss about that.. he said no he wants a regular spray coating... equipment not available to do thermal spraying. i really wanna know whts a typical lifetime though.. IS 12944 i think said that 2 pack epoxies with certain paint systems can yield over 15 years life. but im not sure if that applies to CTE

RE: Coal Tar Expoxy Performance

5 years is an outstanding performance on a pontoon across the river, most likely with suspended solids abrading constantly the coating. Obviously, the smallest crack will expand in time and undermine the lasting performance of the rest of coating. I think the surface preparation is the key thing for you. However, on site you need a ruthless paint supervisor with a whip in hands and the paint spec printed on his back.

RE: Coal Tar Expoxy Performance

(OP)
i get the suspended solids affecting the bottom but the corrosion problem is mostly occurring on the topside. The underside of the pontoons are fairly okay. maybe the application procedures needs to be a little tighter and better surface preparation.

the topside has some gunnels, manholes bolts, etc.


very cool forum btw. its nice to have some other Engineers to talk problems through. The engineers in my country are okay but not many are versed in proper corrosion mitigation because they aren't many large steel structures that arent galvanized or covered in my country. this bridge is the largest steel structure of its kind in my country. i think it was once the longest floating bridge in the world.

RE: Coal Tar Expoxy Performance

Perhaps you have to reconsider the salt content of the water? On the top structure you will experience evaporation which in turn raise the chloride concentration in spots way above the 20000 ppm of the normal sea water

RE: Coal Tar Expoxy Performance

Perhaps the paint on top is subjected to uv radiation damage, which is common for aromatic epoxy. A uv-resistant topcoat may be necessary, e.g. urethane, siloxane, etc.

RE: Coal Tar Expoxy Performance

(OP)
These are all really good points guys. I'll take them into consideration.

RE: Coal Tar Expoxy Performance

What was the original paint specification: DFT, number of layers etc, and what is the specific type of failure being experienced? Are you applying exactly the same coating each time? Has the manufacturer changed the formulation without you knowing? It's no use us taking wild guesses until we know what you started with and how it failed. Once you are into an in situ maintenance scenario, paint lifetime will be degraded anyway. Get professional help on site to identify the failure and to assist with remedial work.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

RE: Coal Tar Expoxy Performance

(OP)
Its the Targuard Coal Tar Epoxy from Sherwin Williams being used.

Manufacturer's Specs:

DFT: 400 microns

No of Coats: 2

Mostly Pitting Corrosion is occurring and localized to the top side of the pontoon.

Manufacturer Formula Not Changed.

RE: Coal Tar Expoxy Performance

So how is the paint actually failing in order to allow pitting corrosion of the substrate to occur? Is it cracking, peeling, blistering?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

RE: Coal Tar Expoxy Performance

I'm with CoryPad. Until we have more information, UV/solar initiated degradation is the most likely, and this is typically prevented with a UV-blocking topcoat, such as a highly pigmented polyurethane. If it wasn't going right down to the waterline, acrylic latex works very well as a topcoat in atmospheric exposure.

RE: Coal Tar Expoxy Performance

Your picture shows almost all of the corrosion is on corners which are exposed to chipping due to impact with tools, shackles, etc.

RE: Coal Tar Expoxy Performance

I agree that edge/corner issues appear to be a big factor. It does look like fading/chalking exists too. You may need a multi-coat system, something like a zinc-containing primer, epoxy mid layer, and polyurethane topcoat.

RE: Coal Tar Expoxy Performance

(OP)
Thanks guys, I think they guys who were in charge of quality checking maintenance works slacked off. Those edge and corner issues seem to me like they were also influenced sloppy sanding and spraying.

anyways I'll try to source a Zinc Rich Primer and Poly Urethane topcoat and add that to the existing paint system. has anyone ever used a paint system like that though?

RE: Coal Tar Expoxy Performance

Those are standard products for marine environments.

RE: Coal Tar Expoxy Performance

Um, I would not try to add a zinc rich primer and polyurethane topcoat to the existing system. I don't know of any manufacturer who uses CTE in combination that way.

I see four basic reasonable choices, depending on availability, cost of downtime, et cetera.:

1) CTE, plus a maintenance/touchup cycle after 1-2 years to fix the sloppy edges/corners.

2) CTE for the main coating system, plus some type of UV blocking topcoat. Check with your supplier for a recommended topcoat.

3) High-ratio inorganic zinc silicate primer alone. With a good IOZ and good surface prep, this works quite well.

4) IOZ, epoxy midcoat, urethane topcoat.

IOZ is more application sensitive (ie, you can get away with sloppier surface prep with CTE) and you have to be sure you're getting a good IOZ like the original NASA formulation.

RE: Coal Tar Expoxy Performance

The most important factor, IMO, in coating performance is the quality of the surface preparation and environmental conditions dutin coating application and cure. Perform a high quality surface prep, and you should be able to get 10 - 20 years of service. BUT, just try to convince the folks with the checkbooks that it's worth it to provide a near-white blasted and maintain humidity control.....

RE: Coal Tar Expoxy Performance

(OP)
Hey guys, sorry for the delayed response. I'm settling to recommend the Primer, CTE and Poly Urethane system. I was checking through ISO 12944-5 Table A5. I noticed it had under Primer it had both "primer type" and "binder" i am a bit confused since as far as i know, primers are standalone coatings (then most of the time overlain with another coating) i.e. they do not need to be mixed with any binder.

can someone clarify?

RE: Coal Tar Expoxy Performance

Any coating, including primers, have multiple components: binder, solvent, pigment, etc. That table shows the binder type, and shows whether the primer is a zinc-rich style or other.

RE: Coal Tar Expoxy Performance

Andy - hire a coating consultant as it appears to be out of your comfort zone. If you look at the CTE datasheets you will note that very rarely are topcoats recommended. If you can get hold of ISO 20340 it would be more appropriate to the application in question. You can then request the paint manufacturers to support their recommended systems with the requisite test reports to substantiate their performance claims.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

RE: Coal Tar Expoxy Performance

Andy,
Listen to the people on the forum, they want to help you. First, you need someone real professional help for this project, use the help as advised, then spend some time to learn what you still don't know for your own benefit and for working similar jobs. This forum is only indication for what you are suppose to learn, is not a substitute for your experience.

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