arc spray metallizing vs PE coating

[basakglkn]

Dear All,

Do you have any opinion of using arc spray metallizing zinc or aluminium+sealer inside of
Sea water pipeline instead of polyethylene coatings?

Have you ever come across such a subject in your projects?

Do you have any idea of year based resistance according to polyethylene coatings?

Your responses would be highly appriciated.
Thank you in advance.for your assistance.
Best Regards,

�. Ba?ak G�LEKEN
Metalurgical Engineer

[Alexangel1226]

Basak,

Not so sure about PE coating, but Arc spray metallizing zinc/ aluminum provide genral corrosion resistance or for electrical insulation purpose other than its well known function, but to resist corrosion by sea water, I am not sure because generally arc spray coating is relatively rougher in surface profile and with higher tolerance of porosity within the coating layers. Chemical, water or fluidized aqueous may penetrate even with sealer applied on it after coating. Youprobably need a higher desity coating for sea water corrosion protection. As I am not expert in this area, would like to know more also.

I come across an interesting article or webpage of experiment conducted to studyThe Effect of the Thermal Spray Process on the Protective Behaviour of NiCr Alloy in Seawater, and the results of the electrochemical investigation of the corrosion properties of thermal sprayed Ni80Cr20 coating as compared to the behaviour of "standard" mass material. It is interesting to know that HVOF being the dense coating is contributing better protective value compared to APS, and most importantly the oxide level in the density has better corrosion resistence towards sea water.

With this study reference, maybe you could consider HVOF process using a better material instead of ARC spray process.

Pls see http://www.corrosionsource.com/events/in...jling.html

Regards,
Alexangel1226

[jeffsays163]

Heard of Arc spray process for Sea water corrosion resistance, instead of PE. But not too sure about how many years it can stand. HVOF is certainly a great process for this application, the cost issue usually limits its expanding.

[Stuart Milton]

Please can you confiirm if you mean the pipeline is under the sea or if the pipe is to carry seawater?

As some of the other posters above, I do not have any information or knowledge of PR coatings. However, arc spraying is done inside pipes for various applications. The issues that you need to consider are the physical dimensions of the pipes themselves. For example, small diameter pipes (less than about 100mm) can only be sprayed internally with an arc extension to a depth of about 1.5m. If you need to go longer than that, the pipe would need to be around 450mm ID. You would have to mount an arc pistol on a fixture and preferable rotate the pipe and traverse the pistol along the inside of the pipe. Depending on the consistency of the pipe diameter, you can have problems doing this. If the pipe diameter is large enough to climb into, you can hand spray. In all cases, you have to consider dust extraction, otherwise you have safety risks and potential for bad dust inclusion in the coatings.

Regarding the material selection (zinc, aluminium or other more exotic materials), this depends on the environment and what the pipeline is carrying. To respond to Alexangel1226, aluminium is most commonly used in seawater applications. Many of the off-shore oil rigs around the world have their support jackets (steel sub-structures, cellar decks, super structures etc.) For a pipeline application with external coating, oil risers pipes that are used to transfer oil and mud products during off-shore drilling are commonly coated with aluminium (around 200 microns) and sealer (to full penetration). For atmospheric coating lifetimes, I suggest that you refer to EN ISO 14713 for independent life to first maintenance predictions for arc sprayed zinc and aluminium coatings.

So, in summary, arc spraying of pipe internal bores is possible, but you need to consider a lot of factors to do it successfully.

[basakglkn]

Stuart Milton Wrote:Please can you confiirm if you mean the pipeline is under the sea or if the pipe is to carry seawater?
..............
The issues that you need to consider are the physical dimensions of the pipes themselves.

Thanks to all for the replys.

The pipes are carrying sea water and their diammeter is app. 3m (far too large i think?)

[Stuart Milton]

In principle, with the information given, I think that a sealed aluminium arcsprayed coating should be fine against sea-water. You may need to re-consider if there are other contaminants in the sea water.

With a 3m diameter pipe, you could easily spray inside and this has been done. You still need to consider access for blasting and metal spraying then sealing. In principle, this is similar to an off-shore environment and when the pipe is not full, you will have a 'splash zone' where your corrosion is higher.

Still not sure about the benefits over PE coating though. It would be interesting to get other viewpoints regarding that.