We have been in possession of the Kundig PMK 75 for three years. In this time I have come to have a high regard for its ability to detect flaws in the cables. Believe me, it doesn’t miss a thing. I love it for what it can do, but hate it when the repair bills come due. We have gained considerable familiarity with the equipment. We know something of its capabilities and its limitations.
For example: We know that to attempt to run an inspection in a heavy rain or snowstorm results in shorting out the circuits, and that an electrical storm screws up the works. I hope never to find out what a lightning bolt might do to the inside of the recorder.
I think Bobbie, the Kundig PMK 75, and I make a pretty good team.
The equipment “sees” the cable; Bobbie, my wife, runs the recorder and bosses the crew around; and I get to lug all that heavy stuff from place to place. (Mr. Kundig, why did you make it so heavy?)
It is because Bobbie has become so adept at handling the recorder and is able to interpret the tapes as they come off the machine that I have become quite confident in her ability in this capacity.
It is true that the detector “sees all.” It doesn’t miss a thing. When looking at a track strand, it sees not only broken wires, whether visible or not, but sees welds, separation between wires, and minute scuffing. It sees some things we wish it could ignore, like certain vibrations in the cable or places where previous inspections have magnetized the cable. This happens when stops and reverses are made with the full magnet. We sometimes do this when searching for an unidentified anomaly. The trick is to be able to distinguish one thing from another in the trace pattern.
We do a lot of follow-up checking. That is, we make a full, constant-speed, no-stop run, recording the locations of each anomaly both on the chart tape and on a scratch pad. We then make a rerun to search out and visually evaluate all that was found in the first run. On this second run we also take our measurements and lay lengths and evaluate the splices, if any.
In the second pass, we probably locate about 30% of the irregularities picked up in the first run. When we find them, we check them against the trace and Bobbie’s interpretation. We find that of this 30% Bobbie is just about 95% correct. From this, we could reasonably expect about 90% accuracy in the remaining 70% of detected, but unfound, anomalies.
What about the remaining 70%? Well, if it’s a broken wire, we attempt to find it and state the nature of the break in the written report. A broken wire is very readable on the tape, so if it is clearly a broken wire, we visually examine the cable and, if there is nothing to be seen, no accompanying damage or evidence of heat, we simply call it “a broken wire.” If we do find it, we will note the nature of the break, such as factory defect, former chair location, etc. If, within this 70% of detected but unfound anomalies, we find in the trace what appears to be a “light nicking,” we will make a brief attempt to locate it and evaluate it. If we see what appears to be corrosion or rust, we will do the same.
There is little or no difference between traces denoting rust and scuffing. While I agree that the difference can be observed under laboratory conditions where everything is predefined and known, I do not claim, in the course of a field inspection, to be able to state, positively, it is one or the other.
Within the unobserved 70% there are a great many combinations of defects, such as singular plane scuffing caused by a deropement or a hung chair being torn from the cable. These can be combined with external abrasion, interstrand nicking and possibly corrosion. I think, and this is my own personal opinion, an inspector using electronic gear cannot, under normal field conditions, accurately define these borderline and intermixed types of flaws. A broken wire, yes. No argument there. But bullet wounds, lightning strikes, no. The equipment cannot accurately identify them for what they are. This is why an electronic inspection alone is not the answer. It must be followed by a visual examination. This is not only helpful to the quality of the inspection but essential to define the cause and the extent of the damaged areas.
You may ask, “If your machine can’t do all these things, then how much good is it?”
Let me give you an example: There were two ropes, each at a different area. Rope #1 had been in service for a number of years and had been visually inspected on a regular basis. It was a regular lay rope but had not been detensioned and opened for a look at the interstrand nicking. Rope #2 (also a regular lay rope in service for about ten years) had been inspected on a regular basis both electronically and visually by a well-qualified wire rope expert.
In the case of Rope #1, suspecting something was wrong, the rope was removed from the lift. When it was strung out in the parking lot, it literally fell apart. Hundreds, maybe thousands, of pieces of broken wires fell out of it. I had not inspected this rope myself, and when told about it I wondered what kind of readout I would have gotten with an electronic test.
I didn’t have to wait long. I was asked to do an electromagnetic test on Rope #2. The man in charge of this installation knew, and being an honest man told me in advance, that two wires of this 6 x 25 rope were hard and brittle and had broken up badly in two areas.
We ran the electromagnetic test on Rope #2. Believe me, the pens went berserk. There were so many wire breaks in the trace it was impossible to count them. A careful, visual follow-up bore out the fact that they were repeated breaks in the same two wires. So my question was answered.
Had we run a test on Rope #1, I would at first have thought my machine was seriously ill and would have checked it out. I would have then gone back on the rope and read its entire length. Knowing then that something was grossly wrong because I would not have believed that a rope could have so many broken wires, I would have taken note of the application and the history of this rope and then proceeded to open it up to see what was inside.
Yes, the electromagnetic test would have set off the alarm. There were few, if any of these wire breaks that could be seen with the eye because they were valley breaks, but the Kundig outfit would have seen them.
The equipment is not infallible. There have been numerous malfunctions. Most of them turn out to be malfunctions of the circuitry, and we have, with the help of Phil Berger of Enduratek and others, made several modifications. Each time we learn a little more about the equipment, its strengths and its weaknesses. We continue to endeavor to improve our own techniques.
We are currently in the process of strengthening the magnetic field, an undertaking which will enable us to “read” the larger diameter track strands with more precision. Through recent experience we have learned that with the use of half-magnet, there is a point in the diameter size range in which full, 100% magnetic saturation is not achieved. To date we have made considerable gains in this area, and the project is still underway. We hope to find the means to pursue it until we are able to take on the largest track strands in service with full confidence.
We are firm in our belief that a constant-speed, no-stop run with the half-magnet rigged to lift over the slack carriers and tower saddles as necessary is superior to using a full magnet, stopping, disassembling and resetting at each obstacle.
Tower approaches in both directions of travel are critical areas. We do not want the distracting influences caused by slowdowns, stops, startups or the residual magnetism left by this practice. We want to read right on across the saddles if there are no obstructions. We also finish up with a much more reliable meter count with this type of run.
What I am going to say now is not intended to drum up business. I say it simply because it is true. We are very sure and fully convinced that for anyone to simply own and occasionally use an electromagnetic cable inspecting device is not the sole and complete answer to the concept of good, true and valid cable inspections. An electromagnetic inspection without a good visual follow-up leaves much to be desired.
If I were an area operator, and were given the choice between an electronic inspection with no visual follow-up or a plain old fashioned visual inspection by a qualified wire rope expert, I would in all honesty have to choose the latter. The electromagnetic equipment is an extremely good tool. It “sees” very well, but it cannot pass judgment.
After all, what do you want when you pay for an inspection? Do you want someone to tell you, in writing, that you have a good rope, a rope in need of repair, a rope nearing the end of its service life, an unsafe rope that should be discarded? Or do you simply want a list of anomalies?
I think you need to know, and have a right to expect, an inspector to tell you all about the rope you are running — especially when you are paying the bill. These damn inspectors don’t come cheap.
As I’ve pointed out, visual inspections have undeniable value, but they do miss a lot of things; conditions such as bad light, bad weather, too much distraction or the inspector is overworked and tired all detract from the quality of a visual inspection. Even under the most ideal conditions he cannot see all that he should see.
Even medical doctors do not rely completely upon the readout of an electrocardiogram. The cardiogram initiates an “alert” or an “alarm.” It suggests the existence of trouble and suggests its nature; but before proceeding with medications or open heart surgery a heart catherization, angiogram, X-rays and other tests will be utilized to bear out and prove or disprove the findings of the cardiogram.
It would seem, then, that the best inspection possible is a combination. An electromagnetic test, followed by a visual evaluation, is the best that can be had.
