Posted by J. King on April 16, 2004 at 21:55:06:
I service a piece of equipment, called a ballistic prover, that utilizes a cylinder with an I.D. of 25.5 inches. The base metal is 17-4 PH sst. Wall thickness is 1.0625 inches. Overall length is 60 inches. The inner surface is chrome plated.
In operation, the cylinder has a piston that moves back and fourth. The piston has two spring loaded cup seals and a rulon rider. The piston weighs about 250 pounds. Since the piston/cylinder are horizontal with respect to ground, the greatest wear to the chrome occurs on one side of the cylinder.
The liquid medium for this particular application is Liquid Petroleum Gas (LPG). Since the LPG is stored in a salt dome cavern, bryne is present. Also since the LPG is not filtered sand/dirt is sometimes present that creates additional wear problems along the bottom surface.
After about a year of service, the chrome starts to break down and the base metal starts to pit and corrode, and the piston seals fail. At this point, I have to remove the cylinder and have it refinished and replated. Sometimes the cylinder cannot be repaired because too much base metal must be removed so a new cylinder must be used. A new cylinder form the end equipment manufacturer is very expensive. In addition, the customers equipment is out of service from two to three months for repairs, and of course this cost them even more money.
So, what I am looking for is a coating process that can be applied to the 17-4 ph material while providing, hopefully, better corrosion resistance and wear protection.
Your input and suggestions appreciated.
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