4-inch Enclosure: 3-Month Post-Deployment Review & Corrosion

Blue Robotics Products Watertight Enclosures
1

Hello,
We are a marine technology company headquartered in South Korea. From February to May 2025, for approximately three months, we deployed a 4-inch x 300mm enclosure equipped with a lithium-ion battery in the Yellow Sea at a depth of approximately 28 meters. We would like to share our observations regarding the equipment’s condition and corrosion post-operation, along with some inquiries.

Deployment Overview
• Location: Yellow Sea, South Korea
• Depth: Approximately 28 meters
• Environmental Conditions:
o Gravel and mudflat terrain
o Significant tidal range and strong currents
Photo-Seabad

Post-Recovery Inspection Results
:wrench: End Cap with Connector
• Appearance: Overall, the exterior maintained a clean condition.
• Surface: Only minor signs of wear or discoloration were present on the surface.
• Subconn Connector Interface: Corrosion was observed up to the O-ring seal.
• :camera: Photo ① – End Cap Comparison

edcap_comparison
edcap_comparison1280×591 80.7 KB

o Top: Connector end cap in good condition
o Bottom: Opposite end cap with observed corrosion
:wrench: Opposite End Cap
• Anodizing Coating: Partially peeled off.
• Stainless Steel Bolt Fastening Area (using bolts included with purchase): Corrosion occurred, with 3 out of 6 bolts severely affected.
• :camera: Photo ② – Close-up of Bolt Area

o Localized corrosion and coating delamination were identified around the screw holes.
• :camera: Photo ③ – Detailed Anodizing Damage
o Clear signs of corrosion were visible on the areas where the black anodizing had peeled off and the exposed aluminum.

Corrosion-Related Inquiry
• The reason for the difference in condition between the two end caps is currently unclear.
• Galvanic corrosion between the aluminum housing and stainless steel bolts is a possible cause.
• Inquiry:
o Would the use of Tef-Gel anti-corrosion lubricant help prevent such corrosion in the future?

Material-Related Suggestion
Do you have any plans to release enclosures, end caps, or flange products utilizing PE (polyethylene) or engineering plastics in the future? We believe these materials could reduce corrosion risks during long-term marine deployment.

Future Operational Areas
The Republic of Korea is surrounded by the Yellow Sea, the South Sea, and the East Sea, each with distinct environmental characteristics. This test was conducted in the Yellow Sea, and we plan to share further results after additional deployments in the South Sea and East Sea.
All attached photos are real images taken immediately after recovery in May 2025.
We welcome any advice or opinions from manufacturers and users.

2

seabed
seabed1920×1080 158 KB

3

Galvanic corrosion2
Galvanic corrosion21280×591 94.3 KB

4

Hi @seaplorer

Thanks for doing this kind of long-term testing, I think it’s really beneficial for the community as a whole.

Here at Mission Robotics we use Tef-Gel on all external Stainless Steel fasteners, and have been quite happy with the results - though we haven’t done any extensive long-term testing. But without some sort of dielectric gel, stainless fasteners in aluminum will even corrode in fresh water.

-W

5

Hi @seaplorer -

Thanks so much for sharing! Beyond tef-gel, the biggest benefit to a long term deployment like this is the use of a zinc sacrificial anode, as detailed in this guide. The results you’ve encountered, without tef-gel or zinc match expectations, but significantly better corrosion resistance is possible with them in use! Additionally, keeping the enclosure from physically touching the seabed can also help reduce the rate of corrosion..

6

"Thank you. We installed sacrificial electrodes before deploying the equipment.
The part where the zinc was installed is the part where the anode did not peel off, and the part where the anode peeled off is where the zinc was not installed.
Also, one issue is that the part where the anode peeled off and corrosion occurred was the part that was in contact with the mud. There was a report that mud was covered upon recovery. Monitoring is needed to see if anode coating damage and surface corrosion can occur due to mud.
We plan to retrieve the equipment, which has been deployed for about another three months, around August. We will be able to confirm it then. The corroded “End Caps” and “O-Ring Flanges” etc., will be discarded and replaced with new ones, then reinstalled. We also plan to use the Tef-Gel that was discussed during installation.
“Is it possible that gas emitted from a lithium-ion battery could escape through the bolt fastening area and cause corrosion? (The equipment where corrosion was found did not have a Pressure Relief Valve installed, and the battery appeared to be in good condition at the time of retrieval.)”
Are there any plans to produce “End Caps” and “O-Ring Flanges” etc., from PE (polyethylene) or engineering plastics?"

zink
zink591×1280 114 KB

7

Hi @seaplorer -
The 18650 cells are sealed and do not emit any sort of “gas” during normal operation… this is unlikely to be related to your issue! The pressure relief valve would only allow gas to escape in the event of catastrophic failure, to prevent the enclosure from becoming a bomb!

There are no Blue Robotics plans currently to produce end caps or flanges from plastic - you are welcome to yourself!

Contact with the seafloor can increase the rate of corrosion, due to both galvanic potential Microbiologically induced corrosion…

8

@tony-white Thank you. Once we retrieve the equipment, we’ll make sure to gather your feedback again.