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Inspection of ropes for Austrian Ropeway using modern NDT Instruments A.Russold -TUEV, Vien, Austria S. Belitsky - INTRON PLUS, Moscow, Russia Contact

Steel wire ropes are most significant part of ropeways. Safe use of the ropeways depends directly on the rope condition, on the in-time and reliable rope inspection. Magnetic flaw detectors are used to determine rope wearing. They can measure the rope loss of metallic area (LMA) and detect the rope local faults (LF) like broken wires and other faults [1,2].
Rope NDT at aerial ropeways differs from rope NDT at mine hoists, cranes and elevators. The difference is specified by construction of the ropeways, by rope wearing character by NDT condition.

The carrying rope is immovable at reversible aerial ropeways, therefore magnetic head of flaw detector must move along the rope during testing. There are one or several towers supporting the rope between stations at this type of ropeways. Difficulty appears by NDT due to this. Meanwhile, the carrying rope is subjected to wear mostly on the towers by cabin passage over them. Some companies produce special magnetic heads with one-side access to the rope under test to pass over the tower. But rope NDT practice in Austria does not suggest rope testing on the towers because of low reliability of testing data due to big ferrous mass influence. Instead of this the rope is tested only between the towers where two-side access to the rope is possible. Meantime, the rope is displaced along periodically. Due to this the rope wears out more uniformly and inspection of the rope part, located on the tower earlier, is possible.

The ropes of locked or spiral types are used mostly as carrying ones. They have the maximum ratio of rope metal area to rope diameter. This requires high power of the flaw detector magnetic system for magnetic saturation of rope material. Besides, use of AC electromagnetic systems is impossible because of high shielding of electromagnetic field by the external wires of the rope.

The design with one ring haulage rope is used mostly at modern aerial ropeways. The rope in this case can be tested completely locating magnetic head at the most convenient place. The rope length can be as much as 5 km and more and there are one or several splices in the rope. The splice increases the rope diameter for (10-20)% and the metallic area for 16,6%. So flaw detector must store big value of information for next analysis.

Fig 1: Intros magnetic head location on the ropeway supporting tower in Austrian Alps.

Another problem appears by rope testing of some types of airways, where available place for magnetic head location is only at the edge of tower (Fig.1) or on the roof of moving cabin. The place is located rather high often. Therefore the flaw detector must be as light and portable as possible and be convenient for fast preparation of magnetic head for rope inspection. It is useful to arrange full set of the flaw detector (including magnetic head and data acquisition unit) on the rope for the next rope testing without any operator.

The ropes of ropeways have low LMA value unlike mine hoist ropes due to rubber lining of pulleys and to insignificant corrosion. The main faults of the ropes are broken wires and disturbance of rope structure because of rather significant bending load on towers and pulleys. That is why the most important parameter of flaw detector is the sensitivity limit to LF. Requirements for the LMA measurement accuracy are not so strong.

TUEV AUSTRIA inspects ropes at ropeways permanently and volume of inspection works within a year is considerable because of many ropeways in Austrian Alps. The comparative testing of modern rope flaw detectors INTROS (INTRON PLUS, Ltd., Russia) and LMA-250 (NDT Technology, Inc., USA) was performed in July - October 1999 to determine their ability for the ropeway rope inspection. The instrument of the Swiss company KUENDIG was used as base for comparison since TUEV AUSTRIA has been using it for years.
The KUENDIG flaw detector is only one-channel instrument: it is able to detect LF. Both other instruments are two-channel: LMA and LF. The KUENDIG and LMA-250 instruments use strip chart recording of analog signals. The INTROS is full digital instrument, which loads testing data about 8 km of rope into a non-volatile storage. The data can be downloaded to a PC for processing and printing of final report. The special WINTROS software is used for data processing [2]. The built-in symbol display is intended for real-time testing as well as an optional strip chart recorder, which can be used for recording current or stored signals. The INTROS is the lightest from the represented instruments, it weights not more 15kg.

The 10 ropes were inspected by all the 3 instruments during the testing. Three of the ropes are carrying ones (two of them are locked type and one is 64mm spiral type) and one is pulling. The rest seven are carrying-drawing type of ring type aerial ropeways. The rope diameter is from 22mm to 64mm.
Besides, lab testing was performed to evaluate detachability of internal LF for all the instruments using special rope standards. Test results of all instruments are approximate the same.

First the KUENDIG instrument was used to inspect ropes, then inspection was performed by two other instruments simultaneously. To avoid influence one instrument to another they were installed on opposite sides of ring ropeways hauling drum. Direction of rope magnetization in magnetic heads was not taken into consideration because special tests have confirmed that the influence of one head rope magnetization on readings of another flaw detector is negligible. When carrying ropes were inspected, magnetic head was placed over a cabin and the head was opened before passing over the tower and then was closed after the passing.

The instruments were calibrated by calibration wire added to the rope under test (negative LMA value). The distance scales of all the recording were corrected by signal of the rope splice.
The result of rope inspection by three mentioned flaw detectors are cited below.

1. LMA measurement
   As well as the KUENDIG instrument has got only the LF channel, the LMA was measured by two other instruments only. Both of them show approximately the same ability to detect LMA when the fault section is rather short (Fig. 2,a,b, three faults located at 783-787m). This ability usually is named as averaging length for LMA.

   a)INTROS	b)NDT	c)KUENDIG
   Fig 2: Segment of haulage rope with additional splice (left) and 3 faults.

   
   The INTROS's dynamic range is wide due to digital method of operation. That is why it can be used without loss of sensitivity by wide range of metallic area change, e.g. at rope splice (Fig. 3,a, from 2786 to 2810m). It is possible to interpret the testing data correctly, meanwhile to do this on base of other instruments readings is not so easy. For instance, section about 765m in the traces Fig.2, where only INTROS's trace shows clearly the additional partial splice of rope strands. Besides, it is more convenient to read data assigned numerical values and to value LMA when the rope length is high.

   a)INTROS	b)NDT	c)KUENDIG
   Fig 3: Rope segment with splice.

   
   
2. Detection of LF like broken wires.
   All the instruments appear approximately the same detectability of the LF like broken wires during lab testing. There are some LF in real ropes which were detected by two flaw detectors but were not detected by the third one. Meanwhile combinations of the instruments can be various. The possible reason of this is difference in LF sensitivity limit of the instruments for definite LF types. Hence, no one of the instruments submitted is guarantee detection of all LF detected by other flaw detectors.

3. Detection of internal LF in ropes of locked and spiral types.
   As it mentioned above this problem is rather hard. The INTROS and the LMA-250 instruments demonstrated ability to detect this type of faults (Fig. 4).

   Fig 4: Locked coil rope with internal localized fault (Intros traces).

4. Inspection of the ring ropeways splices.
   Inspection of that section of a rope is actual problem since wires experienced additional loading because of rope lower elasticity in the splice places. That leads to break of wires as it can be seen on Fig. 4 traces.
   The INTROS is able to inspect this place as well using LMA channel without additional arrange of the instrument.
   Thus, the comparative testing of magnetic flaw detectors produced by three different manufacturers, shows that two of them, the INTROS and the LMA-250 are most available for inspection of steel ropes at aerial ropeways and their testing data are rather close each other.

References

1. V.Sukhorukov. Steel Wire Rope Inspection: New Instruments. - The 7^th ECNDT, Copenhagen, May, 26-29, 1998.
2. O.Gronau, S.Belitsky, V.Sukhorukov. NDTof Steel Ropes with Magnetic Flaw Detectors: Documentation and Interpretation of Test Result. - In this issue.

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