Un painted SS 304 Versus Painted SS 304 Versus Galvanized Low Alloy St

[bmoorthy]

Conditions: Offshore Marine Humid 50 Dec C
Item: Non pressure but in Support/semi loaded (Spring Holder, or Actuator assembly Tie Rods, Fasteners in Instruments)Tie rods, Bolting material (Studs and Nuts)

Material under Discussion:
1) SS 304 (Solution Annealed) A 193 B 8,
2) SS 304 Painted,
3) Uncoated Low Alloy Steel (A 193 B7 (A 320 L7) grades)
4) Galvanized Low Alloy Steel (A 193 B7 ( A 320 L7)grades)

A) Amongst the above 4, which is the better choice
B) What corrosion test should one conduct to find out the suitability of the material (is B 117 salt spray, suitable test)
C) are there Published Salt Spray test data for the above grades, link or references requested, any NACE or EFC publications?

Thanks in advance

 

[CoryPad]

The alloy choice depends greatly on the parts to be joined and the preload level required. B8 does not provide much strength.

1) this is suitable, but you need to control pitting and SCC
2) a coating might help with pitting and SCC, but coating defects will still allow some of each
3) is completely unsuitable - the corrosion would be severe
4) will provide short life - DNV has data that shows corrosion rate to be 5 to 15 micrometers of zinc per year

B 117 is suitable only with correlation to your environment.

Yes, there are many NACE documents on this subject, but check DNV also.

Regards,

Cory

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