Call us on +44 (0)191 646 1000

Rigging

  • 91. Top Tips Tuesday - Protect Your Threads - Galling

    P1070359

    Last Tuesday in my TOP TIPS TUESDAY blog the headline I used was ‘Stainless Doesn’t Rust (or does it)' I then went on to talk in the article about crevice corrosion, and I also stated that crevices can form under welds, WRONG* (but more about that later!)

    Galling is the term used when two surfaces in contact seize up as a result of cold welding. The problem (also known as adhesive wear) is most common in materials such as stainless steel and we in the marine trade come across it occasionally where you have stainless rigging screw body** and a stainless stud or fork. To help prevent galling make sure that the two surfaces are clean and free from any contamination, do NOT use a mild steel brush to help you clean the threads; consider the Shurhold Detailing Brush which has stainless steel bristles and a squirt of WD40. My recommendation after cleaning is to use a lubricant such as Lanocote or Selden Rigging screw oil to lubricate the threads.

    ** most good turnbuckles these days either have a chrome plated phosphor bronze body, or if the body is stainless there is a bronze threaded insert both ends which prevents galling however, threads should still be clean before adjusting.

    Incidentally when mooching round our local boatyard a couple of years ago I came across these very simple homemade covers (made from old bits of hose pipe) for protecting the threads and help keep them clean.

    P1050128-700x525
    Some skippers of course leave their mast up when lifting out, me, I prefer my mast to be down and then you get the chance to check everything out, rigging, nav lights, mast head equipment etc and of course all the fastenings used to hold the fittings in place.
    As a consequence of last weeks article I did get a response from an ‘avid reader’, a retired metallurgist, who wrote and I quote "Your summary of the significant subject of crevice corrosion is fine - that is it is caused by a lack of oxygen in the crevice leading to a breakdown of the oxide film (chromium oxide) that gives stainless steel its corrosion resistant properties (see below image showing the results of crevice corrosion).
    P1070361
    * However you also mention corrosion associated with welds. This is commonly known as weld decay and is brought about by the heat of the welding process causing the chromium present in stainless steel to combine with any carbon present to form chromium carbide - thus depleting the steel in the vicinity of the weld of its essential chromium. (Lose the chromium and you say goodbye to any corrosion resistance). This problem can be overcome, at a cost, by adding titanium to the alloy. Titanium has a greater affinity for carbon than does chromium, hence mopping up the carbon to form titanium carbide and thereby leaving the chromium behind to do its corrosion resisting job". Thank’s to Peter Baylis for putting me right!

1 Item(s)