Another galvanizing question

[PaulJ]

Our anchor chain has had quite a hard life...... It was regalvanised once, not very well and regalvanised again less than two years later, Now, I would like to do it again but I have been told that the galvanizing process weakens the chain and that chain should only be regalvanized twice and then you should buy new chain........ Is this so and if so, why?

 

[Bosun Higgs]

I suppose it must weaken it but how much? The temperature during galv goes up to about 400C so that wont do anything much to ordinary mild steel chain. Stripping off the old galv in acid will likely remove some surface metal but again it shouldnt be much if well managed.

Problem is, will it be well managed - we once completely dissolved the MD's garden gates when an idiot left them in the acid over the weekend. Much amusement in the ranks.

Only you can decide but I can see no reason for strength to fall off a cliff after 2 re-galves. And incidentally, done right it should last more like 20 years than 2, depending on use of course. Personally I would replace but for me its a trade off of cost against lying there in the middle of the night wittering. I'm good at wittering.

 

[MM5AHO]

No galvanizing is done at 400 deg C (The melting point of zinc is 419), more usually at 450C, but occasionally in some specialised processes at 550C.

Regalvanizing results in no measurable weakening of the steel.
Structural steel is galvanized, chains, all manner of things.

The only real concern is in attempting to galvanize high strength, or high carbon steels.
In chains this is usually grade 80, but not very common to use this grade for marine uses like anchor chains. In these case of high grade chains, hydrogen embrittlement can occur in the hydrochloric acid cleaning part of the process. (Though the zinc dipping doesn't cause a problem). In these cases cleaning must be by other means that acid.

Of course long immersion in hydrochloric acid, even the dilute strengths used can cause some erosion of the steel, but responsible galvanizers use a "inhibitor" in the acid. This means that leaving the steel in acid for up to 3 days is OK.

 

[PaulJ]

Thanks to both for your replies.... The chain is "oversize" for the boat (11mm chain, 39footer) so I think I'll risk it. 'Next problem is to find a galvanizer in Preveza!