Monday 12 November 2012

'Stainless Steel' Hose Clips - They Do Corrode!

Not surprisingly and for a good reason, I find that a significant proportion of the time taken to perform a pre-purchase or insurance survey is taken up by the inspection of the boat's skin fittings and associated hoses & clips. I have already described in an earlier blog the all-too-often found skin fittings and seacocks that are made from brass, but another very common finding is the use of hose clips made from poor quality materials. As with the choice of brass material for the skin fittings, manufacturers will select a poorer grade material in order to cut production costs, thus maintaining an acceptable profit margin in an ever more competitive market place.

As part of my routine when inspecting the hose clips, I always check them with a magnet. If the magnet sticks, then I know that the screw, housing or band of the clip is made from mild steel or an inappropriate grade of stainless steel. This check can then be confirmed with a close visual inspection, using a mirror if necessary, looking for evidence of corrosion on the screw or on the band where it is concealed by the housing. Where access permits, I then wield my medium-sized hammer.

The image below shows a result from such an inspection. It was in the stern locker of a 43' Beneteau. It's not easy manoeuvring oneself inside such a locker area, although I've squeezed into smaller spaces on smaller craft. The clip was one of two that was used to secure the engine's exhaust hose to the skin fitting. I could see that the 'stainless steel' clip had been corroding, but it was the light strike from the hammer that broke the band at the point at which it contacts the screw.

Corroded Stainless Steel Hose Clip
Also note that the band of the clip shown in the photo has the kind of serrations that perforate the band, rather than the kind that are pressed into the metal. The perforated type seem to be much weaker in my experience.

The screw, although formed from stainless steel, was most likely a different grade to that of the band and housing. Within a salty and damp environment, the resulting galvanic cell had contributed to the corrosion and weakening of the band. The adjacent clip on the exhaust hose didn't fail when struck with a hammer, but it certainly appeared to be rusting at a similar rate. If my client had gone ahead and bought the boat, it probably wouldn't have had a survey for another five to ten years and in that time both clips would have possibly failed.

One of the most satisfying aspects of being a yacht surveyor is finding defects such as this and then thinking to ones self: If those clips had failed in a heavy sea, at night and whilst motoring (not an uncommon combination), the engine exhaust coolant would start to flood the boat, with sea water entering through the hole in the transom. Would the crew have found the cause in time?

This Winter:

  • Two clips per end fitting where the connection is under the waterline or where the hose coming adrift could cause flooding
  • Check clips with magnet
  • Check for rust on clips
  • If in doubt, remove clips and check for corrosion where band is under the screw
  • Check that clips are tight enough