actuators under sea water

[fatihtezel]

hi everybody.

we are trying to control the water level of balance tanks with pneumatic rotary actuated butterfly valves in an oil-tanker. actuators will be under sea-water when the balance tanks
get full. they have epoxy coated aluminium casting body, and the pinions are galvanized.

what corrosion problems can we meet.
should the actuators PTFE plated or sth, should the pinions
be stainless steel??

thanks a lot..

Fatih Tezel

 

[Sircrashalot]

Depending on the depth to which these actuators are submitted, you may have problems with sea water ingress into the actuator if it is not IP rated for submersion (IP 68 or IP67M I think). If the actuator is rated less than IP 67 you will definately have problems with water getting into the actuator.

For the exposure of the particular materials to sea water, I would contact the actuator manufacturer for their opinion - they may not have been made aware of the posibility of being submerged or directly exposed, and may have a diferent material or product that will better suit.

Andy

 

[bcd]

Hello,

The biggest problem area you are going to have is where the pinion passes through the aluminum housing. Epoxy is too thick to be put inside bearing clearances. Chances are, the aluminum is anodized before coating, which helps, and the pinion is galvanized, which temporarily gives help when first submerged. But eventually, these are mecahnical parts moving in seawater. The relatively soft galvanizing is going to wear and corrode away, and you will have problems with galvanic corrosion between the pinion and aluminum body. Any pin holes or handling damage to the epoxy coating is going to allow the seawater to aggressively corrode the base aluminum. Another issue to consider is biofouling and salt build-up, especially if the actuator is going to alternate between submergence and above surface. Another problem will be crevice corrosion at the o-ring or what ever is sealing between the pinion and housing.

Best solution for these problems depends upon how much is willing to be spent and the acceptable expectation for product life and maintenance.

bcd