Zink plating of hose fittings 1

[Janus101]

Fellow members:
Im currently engaged in following up the fabrication and installation of 2 diesel hydraulic cranes. The Vendor is using hoses in parts of his hydraulic system.

The cranes shall be installed offshore in a saline environment, and part of the hydraulic installations are outside fo the machine house.

I have queried the Vendor about the make and the surface corrosion resistance of the hose fittings, and this is the information I get in return(not much, but it may make sense for some of you)

*Galvanisation, Zink plating, 12µm, and yellow passivation
*Film sealed coating applied on top
*Tested according to ASTM B 117 and ISO 9227
*Requirements given in SAE J516, ISO 4520 and ASTM B 633
*Operating temperature of the hydraulic oil is somewhere in the range of 55 to 65 deg C(131 to 149 def F)

(I guess the hose material is made of "regular" carbon steel)

Anyone have any experience or any thaughts about the above with respect to protection from corrosion?

Thanks in advance.

 

[TVP]

Zinc plating will undergo extensive corrosion in any environment containing chloride ions. ASTM B 633 specifies the corrosion requirement of a minimum of 96 hours until basis metal corrosion (red rust) for this type of coating. The test method is ASTM B 117, which is a salt spray test. More information on these ASTM standards can be obtained from ASTM using the following links:

http://www.astm.org/cgi-bin/SoftCar.../htdocs/astm.org/DATABASE.CART/PAGES/B633.htm

http://www.astm.org/cgi-bin/SoftCar.../htdocs/astm.org/DATABASE.CART/PAGES/B117.htm

The application of a polymer layer ("film sealed coating&quot to the zinc plating/chromate conversion coating specified by ASTM B 633 can extend the corrosion resistance to possibly several hundred hours of salt spray resistance. You will need to make a determination about the expected service environment and the applicability of salt spray testing.

By the way, SAE J516 only requires 72 hours of salt spray resistance. I would investigate a stainless steel fitting for this type of service, possibly Type 316 or something similar-- resistance to chloride pitting, etc.

 

[Janus101]

TVP, thank you very much for the reply.

I have contended earlier that the fittings should be SS316 make, but the vendor objects(of course).