Metal finishing Q&As since 1989

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Rusting Problem

I manufacture stands for studio lights.These stands are made from steel pipes.The pipes are powder coated on the outside. However, these pipes get rusted on the inside. The person I get the powder coating done from states that the pipes are dipped in a phosphating chemical so as to prevent this problem from arising. However this problem persists. 1.) Is the phosphating chemical faulty ? 2.) Is the process correct.

Please advise.

Rishiraj Singh
- Amritsar, INDIA
2002

It is impossible to answer your questions unqualifiedly from this distance. However, the bottom line is that if you as the customer are unhappy with the product because it is rusting, something somewhere needs fixing :-)

"Phosphatizing" is actually a broad term. The parts could be very simply iron phosphatized in a 3-stage system without a final rinse, or they could be rather elaborately zinc phosphatized in a 7-stage system, and oiled after post-treatment. The exposure could vary from dry indoors exposure to wet salt water environment.

But yes, the process can be improved so that you will experience no rusting.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002

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2002

Dear Mr. Singh, try getting the pipes hot dip galvanised or use a good three in one zinc phosphating process and I think you should have no problems.

ALL THE BEST,

Vikram Dogra
Irusha India - Chandigarh, India

Phosphating coating can rust within 24 hours. It should be sealed to get that extra life. Instead of phosphating you should use a rust converter [on eBay or Amazon] which converts rust itself into a protective coating and can be painted afterwards for good rusting free years. If it's not painted then also it gives around 3 months of rust protection also.Try it out one, I am sure this will solve your problem.

Vinay Golwala
- Bombay, India
2003