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Thruster screws are rusted

Does"t Expect from blue robotics.
I had ordered T100 thruster from your site about 5 months ago.
you are using such a cheap quality of screws, they got rusted in such a very small time. You are taking such a hefty amount of money from us, you should provide a reliable product, also its motor got jammed due to rusting. I am very unhappy , that i orederd this product by spending a huge amount of money.
enclosure: Photos

Looks like an old thruster? They’ve made several revisions which improve the corrosion resistance of the stator/rotor. I think what you’re seeing is more a sign of corrosion inside that’s leading into the screw outside, as opposed to corrosion creeping inside from the screws on the outside. I’m also assuming you’re using this in saltwater, because they don’t usually get like that in freshwater. Are you rinsing everything off with freshwater as soon as it’s on deck?

Hi @sanidhya33,

I’m sorry to hear you are disappointed in your experience with your T100 thruster.

We use passivated 316 stainless steel fastening hardware throughout all our products. This is commonly accepted as a marine appropriate grade of stainless steel, and is far more corrosion resistant than most common grades of stainless steel including 304/18-8. Though some “tea staining” of the surface may occur over the long term, this remains isolated to the surface and be a cosmetic blemish only for any reasonable length of time.

However, your images show corrosion far beyond surface tea staining that has obviously affected functionality. We have never before seen this level of corrosion on any of our fasteners, including an ROV that was lost in open ocean and miraculously recovered about a year later hundreds of miles away.

I suspect it may be something about the conditions your thruster was run in, can you share some more information about that? Environmental conditions (salt/fresh/chlorinated water, chemical contaminants), abrasive/ferrous particle content, usage cycle (how long in/out of water and how many times) and anything else noteworthy would be good to know. Was the thruster rinsed with freshwater after use?

Please contact our support team at support@bluerobotics.com with your order number and further details.

-Adam

Thanks for understanding my issues.
as you mention that your suspect is that environmental condition.
we are using thruster in freshwater in our university, we are testing our ROV in a pool having unchlorinated freshwater, which is pure. we tested our ROV about 2 hrs a day and the rest of the day, we place our ROV in a dry place. we are not able to analyze the reason for rusting. so most probably we thought that its manufacturing defect.
The environmental condition in which we are using ROV is mostly less humid and sunny.
some picture of our testing pool

Hi @sanidhya33,

Okay, thank you for the information. In those conditions, you should not be be seeing corrosion anything like you are. Please email our support team (support@bluerobotics.com) and reference this thread.

-Adam

Looks to me what you are probably experiencing is galvanic corrosion, your frame and associated hardware look to be aluminum and not all anodized. With dissimilar metals, electricity and different electrode potentials and the pool water acting as the electrolyte you will have issues.

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Yep I agree with Craig.
Your using a metal frame. Seems to me your screws are acting as anodes and sacrificing themselves in the local galvanic circuit. All you need is an electrolyte to cause this. Freshwater or saltwater the difference is only the speed of the reaction.
I suspect given the level of corrosion seen here thats your problem. If you had a none conductive plastic frame this would not happen.
Your solution is to place an anode of a less nobel metal on the frame. It looks like your frame is Aluminium, so use an anode the same as from an aluminium hulled boat.

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Those screws are not contacting the frame only the motor. They look like flat head screws. All the screws I have ever got from Blue Robotics have been hex cap screws. @sanidhya33 Are you sure that these screws are not mild steel screws from a different source?

In our metal frame we are using lot of screws, nuts and bolt of stain less steel but they never got corroded not a single mark of corrosion on other screws , only Thruster screws got corroded.

Hi Sanidhya, try lifting the rusty screws with a magnet if they stick to the magnet they are steel.

316 stainless steel is non magnetic.

Also I think aluminum would act as a anode to steel.

Kind regards,

Iain.