Howard Lennox of Lexington Park, Maryland, asks:
"I'd like to know how to inspect (for corrosion) a chainplate that is encapsulated inside a bulkhead. Are there any nondestructive tests I can perform to determine a chainplate's condition without having to cut into the bulkhead?"
Don Casey replies:
When a through-the-deck chainplate begins to show signs of corrosion, it will almost always be where the deck surrounds the chainplate. If there is a leak around an encapsulated chainplate -- a when-not-if scenario -- the leak can submerge the entire chainplate base in stagnant water, and corrosion will begin. That's why encapsulating a chainplate is a very bad idea, and if you're not able to do a visual inspection, it is impossible to be sure that it will not fail in the future. Although you can x-ray a chainplate in place, the process is not cheap and there's a chance the x-ray will miss some potential flaws. Ultrasonic testing is another possibility, but even under the best of conditions the accuracy of the results depends a lot on the skill of the operator.
Unfortunately, the best way to deal with an encapsulated chainplate is to remove the encapsulation, inspect the chainplate, and then, if necessary, mechanically attach the existing and new chainplates in a way that will produce the required strength but also let you monitor the metal's condition in the future by visual inspection.