reistance check for rigging.

[mikemacdonald]

How does this work. Is it a straight forward meter across the fittings and check all similiar fittings are the same reading, the same with the wire, so many ohms / metre, or does it need a special meter like a megger or multi function tester.
I have one which does all 16th series tests including resistance,2 ohms upwards, megger functions, loop impedance and bonded metalwork testing, have only used it once for continuity on the house.
Any ideas please?

 

[pvb]

I don't think it's a DIY job. Most testers seem to use the Maidsure Rigtester, and compare resistance readings with known readings for sound fittings.

 

[BlueSkyNick]

The measurement is from the outside of a swaged fitting to the wire, so via the inner bit of the fitting. In a good fitting, the resistance is much less than 1 ohm so your meter will only pick up a problem if it is really serious.

There are specific limits to what is a good resistance or not, so comparing one fitting to another is irrelevant.

You need to get the right tool, or the right man who has a tool, to do the job properly.

 

[A1Sailor]

If you get old rigging tested, it passes, and the mast falls down are the testers liable? If so their liability insurance costs might be significant! Unless, of course, they don't give a cast iron guarantee that the rig won't fail - just the readings.
Anybody had theirs tested?

EDIT:
Cast iron guarantee? Geddit?
It's stainless steel... OK - I'll get my coat.

 

[Deleted member 36384]

According to one website they are measuring in mili ohms. The implication is that on new rigging they can tell quite quickly if there is a poor swage because the resistance is noticeably higher. If the new rigging is OK then they establish a set of readings for that particular rigging arrangement. Subsequent readings over the years build up a history and allow a trend to be established. At some point I assume that the trend deviates from normal which indicates the onset of age related damage. All metal that is strained cyclicly, even within its elastic limits, will eventually work harden. The work hardened metal (cold worked) grain structure changes and it increases in resistivity, slightly. I believe that this is what is being looked for and that the tools are very sensitive in order to detect this.

 

[vyv_cox]

All metal that is strained cyclicly, even within its elastic limits, will eventually work harden. The work hardened metal (cold worked) grain structure changes and it increases in resistivity, slightly. I believe that this is what is being looked for and that the tools are very sensitive in order to detect this.

Sorry, not true. 'Work' in the context of work hardening means plastic deformation. Austenitic stainless steel rigging wire starts as rod in the as-cast condition and is drawn through a die that reduces its cross section by about 3%. This is work hardening. It pretty much doubles the strength of the metal in doing so, which means its hardness has doubled also. The grain structure doesn't change, it simply elongates, as you would expect.

I assume that the change in resistance would be because of fatigue fracture of individual strands of wire and galvanic corrosion inside the swage.

 

[Boathook]

If you get old rigging tested, it passes, and the mast falls down are the testers liable? If so their liability insurance costs might be significant! Unless, of course, they don't give a cast iron guarantee that the rig won't fail - just the readings.
Anybody had theirs tested?

I used maidsure when he first started out (20 + years ago?) with his own bit of test kit. Back then N&G accepted the test reults even though the rig was 12 years old. I eventually replaced the standing rigging as a bottle got damaged a few years later.

Edit bit -
http://maidsure.org.uk/index.php?option=com_content&task=view&id=2&Itemid=2
Mentions 16 years here but it was more that.

 

[mikemacdonald]

reistance checks.

Thanks for the replies. Sounds like it will be a waste of time trying to do it myself, may just take the tester down and try it, but I doubt it wil be very good, lowest measurable resistance is 0.01ohms but that won't mean a lot if I don't know what I'm looking at !!!
More research needed methinks

 

[A1Sailor]

Interesting. I replaced the standing rigging, and bottle screws, on my "new" Sadler25 in June. My rig and bottle screws are nice and shiny. Total cost was just under £500. Had I tested the old rigging, 6 wires with 12 terminals, the costs might have been relatively high compared to replacement.
More advantage, methinks, for owners of larger craft.

 

[Deleted member 36384]

Sorry, not true. 'Work' in the context of work hardening means plastic deformation. Austenitic stainless steel rigging wire starts as rod in the as-cast condition and is drawn through a die that reduces its cross section by about 3%. This is work hardening. It pretty much doubles the strength of the metal in doing so, which means its hardness has doubled also. The grain structure doesn't change, it simply elongates, as you would expect.

I assume that the change in resistance would be because of fatigue fracture of individual strands of wire and galvanic corrosion inside the swage.

All I know is that copper wire does change its resistance when it work hardens as you define above. This is from HV surveys I have had done on rigs for condition monitoring of power cables. I also have a vague recollection that that when a metal work hardens (as you define it above) its grain structure changes.

I understand its not cracked strands they are looking for (post new and now in use), it's the onset of plastic deformation that they are looking for and the tiny change in resistance that that causes.

Anyway, I am no metallurgist, I thought that after plastic deformation occurs the grain structure has changed based on the copper wire condition monitoring, I would call permanent elongation a change. Perhaps its this change in length that changes the resistance.

I am sure that cracks and resistance changes at very small levels are two different aspects that they are trying to detect. As always, I am happy to be educated further or for clarity to be brought to my vagueness.

If I take a strand of rigging wire as made by the process you describe, I can work it until it snaps, I can also bend it and it springs back to shape without any noticeable deformation. If I stop wiggling the wire just as at the onset of yielding, what happens to the grain structure?

 

[nigelmercier]

According to one website they are measuring in mili ohms...

That's interesting, with a suitable circuit and a DVM one could measure the rigging regularly and look for changes.

 

[vyv_cox]

.If I take a strand of rigging wire as made by the process you describe, I can work it until it snaps, I can also bend it and it springs back to shape without any noticeable deformation. If I stop wiggling the wire just as at the onset of yielding, what happens to the grain structure?

Where plastic deformation has taken place the grains will be elongated, or their shape will be changed. This photo shows work hardening in a Monel fuel pipe due to cavitation. The metal has been moved by the impacts and thus hardened. Grains in the body of the pipe are equiaxed and fairly round, whereas near the surface they are elongated.

The diamond indents are made by a Vickers hardness tester and the numbers alongside are the values, where higher=harder.

In your query above, the microstructure is austenite, determined by the composition of the alloy. Nothing in normal use will change it - austenitic steels are not heat treatable because of this. This also applies to your copper, which as a single phase can be annealed (= recrystallised) to remove the effects of work hardening but its microstructure is fixed.

 

[Deleted member 36384]

Thanks for that. Perhaps then the condition monitoring of the copper wires is picking up snapped strands.

 

[vyv_cox]

I do know that pure copper work hardens quite readily, probably more than stainless steel does. Would these cables be free to vibrate, producing plastic deformation at the connectors? I could certainly believe that the elongation/deformation of grains could cause resistance changes.

 

[Deleted member 36384]

I do know that pure copper work hardens quite readily, probably more than stainless steel does. Would these cables be free to vibrate, producing plastic deformation at the connectors? I could certainly believe that the elongation/deformation of grains could cause resistance changes.

The cables move as the rigs skid across different well slots. On some rigs its just a cantilever device, on others a drag chain (caterpillar track) and on some just a bundle in a net sheave. So there are points in the cables that are subject to bending loads. They can be subject to vibrations but not anything considerable. Many have been in place for 30 years now.