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304 steel and aluminum contact in hydraulic fluid

2005

Dear sir/madam
Because of corrosion problems in magnesium hydraulic fluid reservoir (casted),
I am designing an 304 stainless steel container (welded construction).
5052 Aluminum alloy hydraulic lines are connected to reservoir by aluminum 2024 or 2014 fittings.
Because of some other facts, I could not anodize aluminum fittings, I may only passivate 304 reservoir.
Does a corrosion problem occur in this combination?
Best regards,

Oguz OZBAY
5 th Maintenance Center - Ankara, TURKEY

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Why not use an aluminum reservoir with the aluminum fittings and lines? Also, Al 6061 fittings are less corrosion-prone than the Cu-containing 20x4.

With your new design, the stainless won't corrode, but one cannot say more because there seems to be a problem of excessive moisture in the hydraulic fluid. Three ideas: Use a less hygroscopic fluid, change the fluid more often, and use a rubber bladder or diaphragm in the reservoir to allow fluid volume change without direct air contact.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2005

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2005

Dear,
Ken Vlach (also other readers)
First of all, thanks for your answer.

There are a few reasons that we built a stainless steel (CRES) reservoir.

1- CRES is easier to weld & more reliable welds (isn't it?)
2- Because of being capable for welding almost 0,8 mm thickness, CRES is light weighted (0,8 mm CRES reservoir have equal weight with original magnesium one, almost 3 kg lighter than 4 mm aluminum -- 4 mm Al seemed me sufficient thickness to weld)).
3- I, first, thought to manufacture aluminum, approx. 4 mm but CRES is easier (and light weighted) to build. But of course, if it is appropriate for my situation.
Thus I asked it here.
4- Because of some other facts (logistics) it is not possible to change fittings to 6061 Aluminum
5- Weight is a consideration.
6- I know, I do not write good sentences with my insufficient English, Sorry.

Best Reards,

Oguz OZBAY
5 th Maintenance Center - Turkey

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The new design is definitely an improvement. The 304 SS and Al 5052 probably will remain passive, but best to inspect periodically. Watch for corrosion of the Al 2024 threads (formation of white aluminum hydroxide) of the compression fitting. If this occurs, apply a non-hardening thread sealant/lubricant to the external SS threads of the fitting. PTFE-containing sealants are suitable; copper and graphite types are not. PTFE tape on the external threads might work and is easier to try.
Good luck.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2005