How effective is the non-destructive

examination of multi-layer, low rotation

winding ropes?
by M. Dohm*

Certification Committee (SAQCC). Application

of the code has led to enhanced safety and a
Synopsis reduction in operating costs.
Parallel research indicated that six
The paper reviews the results emanating from an experiment stranded rope constructions, so commonly
conducted in Bochum—Germany in which various international used in South Africa, may not be suitable for
rope inspection authorities were requested to assess the conditions
hoisting from great depths and that multi-
of a corroded rope sample as well as a rope sample containing
layer, low rotation ropes may be required for
internal fatigue breaks. Both samples were of the multi-layer low
rotation construction. this application.
Rope trials, funded by the Anglo American
Corporation of South Africa Limited, Gold and
Uranium Division, involving 48 mm diameter,
low rotation, 15-strand fishback ropes at Vaal
Reefs 9# during the early 1990s indicated that
Introduction and background the NDT results of such ropes were suspect. In
the final report relating to this rope trial the
The South African Minerals Act and
following was stated: ‘Internal deterioration
Regulations required that ‘A winding rope
was suggested by anomaly indications
shall not be used if the breaking force at ANY
appearing where no rope outer wire fractures
POINT in the rope is less than nine-tenths of
were visible. Since the nature of this deterio-
the original breaking load’. ration was unknown the condition of the ropes
The question of establishing the remaining could not be assessed accurately on the basis
strength accurately at any point along a rope, of the non-destructive, magnetic rope tests’3.
using non-destructive methods, has been a Numerous samples were cut from the ropes
point of debate for many decades. after discard. Three sections were de-stranded
In the 1980s South African mining houses to ascertain the actual condition of the rope. It
started identifying means of hoisting is interesting to note that no broken wires had
economical payloads from very deep shafts. occurred on the 9 outer strands of any of the
One of the issues raised during these investi- rope samples. It was, however, disturbing to
gations was the efficacy of rope condition find 148 broken wires on the inner six strands
assessment. The investigations indicated that of two of the 2-m long samples. In one sample
no common standard existed internationally 21 broken wires were found in an axial rope
for rope condition assessment. Tests of length of 100 mm. Figure 1 indicates the
discarded ropes also indicated that the positions of the broken wires.
remaining strength varied greatly. These results clearly indicated that the
Numerous projects were funded, initially non-destructive testing methods employed by
by the Chamber of Mines of South Africa, later the South African mining industry at that time
by the Government, which addressed mine were not able to detect broken wires located on
hoisting ropes in general and the condition the inner strands of multi-layer ropes.
assessment and discard criteria of ropes in Representatives from the mining industry
particular. The focus was on six stranded proposed a project to ascertain the defect
ropes as these are predominantly used in the detection capabilities of magnetic rope test
South African mining industry.
This work culminated in the publication of
the SABS 0293: 1996: Code of Practice:
Condition Assessment of Steel Wire Ropes on
* Mechanical Engineering, Johannesburg, R.S.A.
Mine Winders. This code is now applied
© The South African Institute of Mining and
throughout the South African mining industry Metallurgy, 2000. SA ISSN 0038–223X/3.00 +
by rope inspectors certificated in terms of the 0.00. This paper was first published at the SAIMM
code by the South African Qualification and Colloquium, Mine Hoisting 2000, Sept. 2000.
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The Journal of The South African Institute of Mining and Metallurgy NOVEMBER/DECEMBER 2000 437
How effective is the non-destructive examination
instruments in respect of multi-layer, low rotation rope Furthermore, the non-destructive examination could
constructions on an international basis. This paper describes either be conducted by an expert using his own instrument
the results of the project. and performing the analysis of the instrument output signals
himself whereafter the expert would submit a detailed report
Literature survey regarding the condition of the rope sample, or the researcher
could subject each instrument to a series of pre-defined tests
Little reference was found to the actual resolution obtained and then analyse the outputs from the various instruments
by magnetic rope test instruments in the non-destructive and draw conclusions for each instrument tested.
testing of multi-layer, low rotation ropes. From the literature survey it was quite clear that the
While some of the papers suggest that internal broken efficiency of rope NDE is to a large degree dependent on the
wires can be identified accurately by means of magnetic rope expert using his own instrument and his experience plus his
test instruments, others seem to indicate this to be understanding of the ropes being tested and his instrument.
problematic, especially where a multitude of broken wires It was therefore decided to contract world-class rope NDE
exist within a multi-layer, low rotation rope. experts to conduct the examinations and for them to submit
Similarly there are varying opinions regarding the detailed reports.
remaining strength of corroded ropes. In some quarters there
is the belief that sophisticated algorithms built into the Choice of NDE experts
instruments can lead to accurate predictions of the condition
of corroded ropes. Eight organizations were identified as having expert
The literature survey clearly indicated that there is no knowledge in the field of rope NDE. Several of these organi-
simple solution to the accurate identification of internal zations produce the rope test instruments used for the
broken wires and the estimation of remaining strength of examinations as well. Most have produced several papers in
multi-layer, low rotation ropes. the field of rope NDE and have conducted research in this
field.
Research methodology The following were invited and accepted the invitation.
➤ NORANDA, from Canada
Choice of methodology ➤ Lloyds Beal Limited, from the United Kingdom
➤ DMT—Gesellschaft für Forschung und Prüfung, from
The basic methodology proposed for the experiment was to
Germany
fit a rope sample from the Vaal Reefs 9# experiment into a
➤ NDT Technologies, Inc. from the USA
tensioning device and to have the rope examined non-
destructively by a number of expert rope inspectors. After the ➤ Universität Stuttgart—Institut für Fördertechnik, from
non-destructive examinations had been completed samples of Germany
the rope would be destranded into its individual components ➤ AATS—from South Africa
to establish the position of each broken wire or destructively ➤ The University of Mining and Metallurgy in Cracow,
tested to ascertain its remaining strength. The NDE results Poland. (The University withdrew from the project
would then be compared to the actual condition of the rope during the year because of high workload. The Polish
sample to establish the detection capabilities and resolution instrument supplier Meraster was identified as a
of the instruments. substitute)
It was decided to employ a discarded rope from the field ➤ Rotesco Inc. from Canada
with an unknown distribution of internal broken wires
instead of a manufactured rope sample with known internal
defects. The manufacture of rope samples with known Choice of testing laboratory
defects is possible but time consuming. The resultant defects Several test facilities were identified in Europe, South Africa
are not necessarily a replica of the wire breaks experienced and the United Kingdom. It was decided to conduct the
under operating conditions. The choice of rope sample was experiment at the DMT—Testing and Transport Technology
discussed at a meeting with mining representatives and it Laboratories in Bochum, Germany because two tensile
was unanimously decided that rope samples from the field be testing machines of suitable capacity and length were
employed. available in one hall at the DMT. This facility allowed the
NDE to progress in quick succession. The location is also
convenient from a logistics point of view. Four of the NDE
organizations were able to travel by car to Bochum.
Facilities were installed at both tensile test benches which
allowed the test heads to be pulled back and forth over the
ropes at various pre-determined speeds in a controlled
manner.

Choice of rope samples

Figure 1—Position of broken wires within a multi-layer, low rotation As stated earlier, it had been decided to employ discarded
rope sample rope samples from the field for the experiment.
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438 NOVEMBER/DECEMBER 2000 The Journal of The South African Institute of Mining and Metallurgy
How effective is the non-destructive examination
Corroded rope sample remaining strength of the rope and to substantiate the
remaining strength estimates with calculations, calibration
The researchers were able to source a unique 36 mm
procedures, instrument traces, etc.
diameter, 21 strand—21 (9 x 6 x 6) construction, multi-layer,
low rotation rope of some 23 m length in very good condition Broken wire rope sample
except for an approximately 3 m length exhibiting heavy
The 48 mm diameter rope was installed into the tensile
corrosion. This was an ideal sample because there were no
testing machine and pre-tensioned to 20,8 ton.
broken wires in the sample and the bulk of the rope was in
Each contractor was required to fit his instrument to the
excellent condition, allowing for the calibration of the
rope and prepare for the following tests.
instruments on a good portion of the rope.
Broken wire rope sample Test 1

There were a number of 48 mm diameter, 15 strand 9 x 10 The contractor was required to obtain instrument traces for
the rope, using a minimum instrument to rope air gap of 5
(8/2)/6 x 14 (8/6 + 3T)/WMC fishback, low rotation, multi-
mm for similar conditions as stated previously.
layer rope samples available from the experiment conducted
at Vaal Reefs. Test 2
After discussions with experts in the rope testing field it
was decided to use a rope sample exhibiting the least amount The rope sample, approximately 18 m in length, had a
of damage. In theory, the fewer the number of clusters of magnetic marker taped to the rope at a distance of approxi-
broken wires contained within the rope under test the better mately 6,8 m from one end of the rope. The contractors were
instructed to reference all broken wires identified in the rope
the chances of accurate detection of the broken wires.
by the NDE to this marker.
Various rope samples were examined, non-destructively,
Three sections of the rope were marked off for specific
in great detail by AATS rope inspection personnel at the CSIR
analysis (see Figure 3 for clarity).
premises at Cottesloe. The ‘best’ rope sample, showing the
Contractors were required to examine the marked off
least number of internal broken wires and ‘noise’, was
sections of the rope in detail using NDE methods. Again an
identified and prepared for shipping to Bochum.
airgap of at least 5 mm was specified. Contractors were
allowed to use any instrument velocity deemed necessary to
Test procedures conduct their tests.
After the examination, contractors were required to
Corroded rope sample analyse the data and to submit a report to the researcher
detailing the position and the number of broken wires
The 36 mm diameter rope was installed into the tensile identified in the rope, referenced to the marker for sections
testing machine and pre-tensioned to 9,6 tons, which is 10% DS1 and DS2.
of the ultimate breaking strength of a new rope. The contractors were also requested to submit the
Each contractor was required to fit his instrument to the estimated remaining strength of section TP1.
rope and prepare for the following tests:
Test 3
Test 1
In the third test contractors were allowed, to non-destruc-
The contractor was required to obtain instrument traces of tively examine the rope in any other way they wanted in
the rope, using a minimum instrument to rope air gap of 5 order to enhance the results of the examination.
mm, for the following conditions:
Actual physical condition of the ropes
➤ At an instrument velocity of 0,5 m/s in both directions
➤ At an instrument velocity of 1,5 m/s in both directions After the NDE tests had been completed in Germany the
ropes were returned to South Africa for destructive
➤ At an instrument velocity of 2,0 m/s in both directions
examination.
➤ At an instrument velocity of 2,5 m/s in both directions.
The traces were to be handed to the researcher directly Destranding and destructive testing of broken wire
after the test. sample

Test 2 The broken wire rope sample was sent to Haggie Rand
Limited for analysis.
The rope sample, some 21 metres in length, had a magnetic TP1 was destructively tested to establish the remaining
marker taped 5,35 m from one end of the rope. Two portions strength of this particular rope section.
of the rope sample, each 3,75 m long, were marked off. The DS2 was destranded to establish the exact position and
one portion was in the good section of the rope (test piece 1 number of broken wires relative to the marker within the
or TP1) while the other covered the badly corroded section sample.
(test piece 2 or TP2). See Figure 2 for details.
The contractors were required to establish the remaining Results
breaking strength of the rope at TP1 and TP2, where TP1
should reflect a breaking strength very close to the breaking
Corroded rope sample
strength of the new rope.
The contractors were also required to give an indication Table I summarizes the results of the non-destructive as well
of the methodology employed during the test to establish the as the destructive test results for TP1.
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The Journal of The South African Institute of Mining and Metallurgy NOVEMBER/DECEMBER 2000 439
How effective is the non-destructive examination

Table I
Corroded sample: TP1 results
Actual Estimated % Loss in
Breaking Breaking Breaking
Strength in kN Strength in kN Strength

Breaking strength of 961 - -

the new rope
Results of destructive 947 - Approx. 1,46% Figure 2—Corroded rope sample
test of rope sample
NDE results
NORANDA - No significant -
loss
Lloyds Beal Limited - No significant -
loss
DMT - Nominal of -
new rope
NDT technologies - - Assume 0%
Universität Stuttgart - Approx. 0%
AATS - No significant
loss
Meraster - 800–940 between approx.
2,2% and 16,8%
Rotesco - Less than 1%

Figure 3— 48 mm rope sample with broken wires

Table II
supply more detailed information and to reference each
Corroded sample: TP2 results
broken wire identified to the marker. A number of
Actual Estimated % Loss in contractors reported that this was impossible due to the
Breaking Breaking Breaking resolution limits of their instruments and that reports would
Strength in kN Strength in kN Strength
be submitted detailing the number of broken wires identified
Breaking strength of 961 - - in 100 mm or even 200 mm intervals along the axial length
the new rope of the rope.
Results of destructive 497 - 48,3%
test of rope sample A total of 609 broken wires were identified when the 8
NDE results metre rope sample, DS2, was destranded into its individual
NORANDA 10% best case
components. Rope condition assessment contractors
20% worst case identified between 0 and 750 broken wires in the same rope
Lloyds Beal Limited greater than 14% sample using non-destructive techniques.
DMT between 20%
and 25%
NDT technologies approx. 9%
Universität Stuttgart At least 80% not more Details of results: broken wire sample DS2–8 m length
of new than 20%
AATS approx. 576kN approx. 40%
Meraster 500kN to between 28%
Noranda
690kN and 50%
Rotesco between 30% Test 2 results
and 44%
The Noranda team identified a total of 31 broken wires along
the length of the rope sample using the Magnograph II in
Table II summarizes the results of the non-destructive as
terms of the procedures laid down for Test 2. These
well as the destructive test results for TP2.
anomalies were classified on the trace as:
Broken wire rope sample ➤ Numerous internal broken wires (small diameter)
➤ Localized group of broken wires with added MA
As stated previously contractors were required to assess the (possibly some bent back)
number of broken wires in the designated rope sections. ➤ Single broken wire (large diameter).
Although the researcher requested that each broken wire
Each anomaly was referenced to the rope marker, i.e. an
identified by the NDE be referenced in axial distance from the
exact location for each broken wire was given relative to the
marker, this was not attained in all cases. The resolution of a
marker.
number of the instruments does not allow the inspector to
Only 5% of the actual number of broken wires existing in
pinpoint each broken wire accurately to the nearest mm or
the rope sample were identified.
even 100 mm from a fixed point.
Many of the initial reports received by the researcher
Test 3 results
from the rope inspectors only stated the total number of
broken wires per sample. The contractors were requested to No results were presented.
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440 NOVEMBER/DECEMBER 2000 The Journal of The South African Institute of Mining and Metallurgy
How effective is the non-destructive examination
following comments:
No of Broken Wires

‘All charts show large clusters of broken wires in areas

along the length of the rope at the following distances;
➤ 0,3–0,7 m
➤ 2,5 m
➤ 4m
➤ 5,4 m
➤ 10–11 m
➤ 12,4–13,5 m.
--- Actual Lloyds Beal
Besides these large clusters of broken wires, the LMA
Figure 4—Lloyds Beal: Broken wire comparison for Test 2 at 100 mm
traces show considerable variations of cross-sectional area
intervals along the entire length of the rope. This, together with the
indications of the LF trace, implies that there are innumerable
broken wires and clusters of broken wires along the entire
length of the rope’.
Lloyds Beal

Test 2 results
Lloyds Beal personnel identified 142 broken wires in the rope
sample, which represents 23% of the actual number of
broken wires in this sample. The broken wires identified by
Lloyds Beal were reported in the number of broken wires per
100 mm interval.
The details of the NDE are shown in Figure 4.
The graphs indicate that the inspectors were able to
Lloyds Beal ----- Actual
identify broken wires in areas of the rope sample where
broken wires were physically present. However, some 77% of
the actual broken wires were not identified. Figure 5—Lloyds Beal: Broken wire comparison for Test 3 at 100 mm
intervals
Test 3 results
In this test Lloyds Beal inspectors used a 48 mm diameter
insert in the test head. Results obtained were much better
than in the previous test, in that 291 broken wires were
identified in the rope sample. This represents 48% of the
actual number of broken wires. Such tight inserts are,
however, not practicable in the field where grease covers the
ropes.
More broken wires were identified and there appears to
be a correlation between some of the peaks in the graphs.
DMT
----- Actual NDT TECH
Test 2 results
The team from DMT identified 84 broken wires in the test Figure 6—NDT Technologies: Broken wire comparison for Test 2 at 100
mm intervals
sample which equates to 14% of the actual number of broken
wires in the sample. They initially presented the number of
broken wires in 1 metre intervals. This was later refined to
100 mm intervals.

Test 3 results
No results submitted.
NDT Technologies

Test 2 results
The rope test personnel from NDT Technologies stated in
their report that they were able to identify 636 broken wires
in the rope sample. This is 27 broken wires more than
actually present in the rope sample.
The initial report contained a number of traces and the Figure 7—Stuttgart Universität—3D scan
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The Journal of The South African Institute of Mining and Metallurgy NOVEMBER/DECEMBER 2000 441
How effective is the non-destructive examination
At a later date NDT Technologies submitted an addendum peaks. In these graphs an offset between peaks is noticeable
to the initial report stating the number of wires identified in which may indicate a problem with the axial measurement
terms of 100 mm intervals. system of the instrument. As with the NDT Technologies
Details of the results are shown in Figure 6. results, an understatement of the number of broken wires in
The graphs indicate a correlation between the actual the 5 200 mm area is evident.
number of broken wires and those identified by means of
Test 2 results—RMS instrument
NDT. There is an offset noticeable between some peaks,
which may be due to an axial measurement error in the AATS personnel repeated the test using a second instrument.
instrument. The graphs also indicate an overstatement of the This instrument is directly coupled to a chart recorder and the
number of detected broken wires in the areas closest to the analysis of the results was entirely dependEnt on the chart.
marker and an understatement of broken wires in the In this test 67 broken wires were identified in the sample.
5 200 mm area. The results were submitted in terms of ‘number of broken
wires per 200 mm interval’.
Test 3 results
Test 3 results
In this instance NDT Technologies personnel wound an
annular coil onto their instrument to enhance resolution. No results were submitted.
The rope inspectors identified 750 broken wires in the 8
Meraster
metre rope sample. This is 23% more than the actual number
of broken wires present in the rope.
Test 2 results
Universität Stuttgart
The rope inspectors from Meraster identified 19 anomalies in
the rope sample. These anomalies were each referenced in
Test 2 results
mm from the marker. Each anomaly was described, for
Personnel from the University identified 42 broken wires in example
the 8 m rope sample. This represents 7% of the actual ➤ accumulated broken wires of inner strand
number of broken wires in the rope. The report submitted to ➤ accumulated broken wires of rope core
the researcher identified each broken wire in relation to the ➤ inner, 2 or more wires
marker. ➤ WMC, 2 or more wires
Test 3 results ➤ outer, 2 or more wires.
The researcher was unable to obtain a more detailed
The Stuttgart Universität rope experts also tested the rope
breakdown of the number of broken wires identified by
using the ‘Hochauflösende Magnetische Seilprüfmetode’. The
Meraster.
inspectors identified the same number of broken wires using
this method as they did using their normal instrument.
Figure 7 shows a black and white rendition of a 3D scan. Comments by Rotesco
AATS
a) Position and number of broken No broken wires were positively
wires identified in the rope, identified in the rope from the
Test 2 results—AATS instrument referenced from the marker Rotescograph Test Results. None
(Rotescograph Test) were identified because the
The AATS team identified 341 broken wires in this rope signals from the broken wires,
if there were any,
sample, which equates to 56% of the actual number of were masked or were
broken wires. Some anomalies were classified as ‘large’. indistinguishable from the
Each broken wire identified was referenced to the signals caused by other types
of deterioration, which appeared
marker. to be wear and possibly
The results are reflected in Figure 8 internal nicking.
These results indicate correlation between some of the b) Position and number of any A 64 mm diameter solenoid
additional broken wires coil was placed inside the
identified in the rope from other Rotescograph Test Head and
tests (Solenoid test) the rope was tested using this
solenoid coil. The output
from the solenoid coil was
integrated to provide a signal
of the loss of metallic
cross-sectional area. Based
on the test results from the
solenoid coil, no broken wires
were positively identified in
the rope. None were identified
because the signals from the
broken wires, if there were any,
were masked or were
indistinguishable from the
signals caused by other
types of deterioration, which
------Actual AATS appeared to be wear and possibly
internal nicking.
Figure 8—AATS: Broken wire comparison for Test 2 at 100 mm intervals
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442 NOVEMBER/DECEMBER 2000 The Journal of The South African Institute of Mining and Metallurgy
How effective is the non-destructive examination
Test 3 results Table III
No results were submitted. Remaining strength comparison of 48 mm rope,
Rotesco TP1
Test 2 results Strength of TP1 % Reduction
in strength
Rotesco identified no broken wires in the rope sample.
Breaking strength of new rope 2080 kN
Test 3 results Actual remaining strength 1452,7 kN 30,2%
as determined by destructive test
A solenoid coil was wound into the instrument for this test. Noranda - -
Using this method no broken wires were positively identified Lloyds Beal - -
DMT - -
on the rope. NDT Technologies - -
Universität Stuttgart - -
Results of Test No 1 AATS - -
Meraster - -
A quantitative comparison of the traces was difficult because ROTESCO 4% to 6%
of the different chart speeds used for different tests.
The analysis of the traces indicated that the velocity of
the instrument and the direction of travel influenced the is calibrated) with the measured MA in another section
output signal of certain of the instruments. This can affect of the rope (the deteriorated section). The
the repeatability and accuracy of the rope condition measurement of the LMA should be relatively straight-
assessment. forward.
➤ The values presented for %LMA varied from 9% to
Remaining strength of section TP1 45%, in relation to the good section of the rope. This
The rope condition assessment contractors were all requested indicates that calibration and measuring procedures are
to determine the remaining strength of the rope section not universal nor adequate. Different instruments used
designated as TP1 in the 48 mm rope sample. to measure the same rope section should at least give
Only one took the challenge. reasonably similar LMA values.
The fact that only one contractor tried to estimate the ➤ The derivation of the loss of breaking strength (LBS)
remaining strength of the rope sample gives an indication of was presented in different ways by the different rope
inspectors. Some of the experts used formulas to
the complexity and difficulty in estimating the remaining
calculate the LBS, others used graphs, some multiplied
strength of ropes.
the LMA value by two while others halved the LMA
DMT experimental rope containing artificial defects value they had recorded. One inspector gave the
remaining strength estimate within a very wide
The DMT made their in-house experimental rope available for
tolerance band.
further tests to all of the rope inspection organizations which
➤ The rope condition assessment experts calculated LBS
took part in the Bochum experiment. The experimental rope
values of between 9% and 50%. This must be
is a multiple oval, flattened strand rope of 48 mm diameter
compared to the actual value of 48,3% LBS established
and SES-U+7x[1+6+(6+6)+16] construction. The rope is
by destructive testing.
mounted on a vertical position and the test heads are moved ➤ The above also indicates a lack of consistency in the
up and down over the rope by means of a crane. methodologies and standards rope inspectors apply to
The rope has a number of artificial defects built into it determine the loss of breaking strength. This fact
ranging from single broken wires to a broken core. should be of grave concern to users employing ropes in
All 8 rope inspection teams were able to identify every critical applications.
anomaly in the rope. ➤ The researcher is not keen on relying on the
proprietary algorithms proposed by certain inspectors
Analysis and discussion for assessing the condition of ropes. These proprietary
algorithms lead to a ‘black box’ approach. The user of
Corroded rope sample the instrument generally does not understand the
➤ The wide variation in the remaining strength values reason for rope discard when using this proprietary
submitted by the different rope inspectors gives an technology built into the instrument.
➤ For the algorithms to be useful every combination of
indication of the complexity and the unknowns
rope construction, deterioration mechanism, rope
inspectors have to contend with when deriving the
diameter, tensile grade and instrument characteristic
remaining strength of corroded rope sections. The wide
needs to be tested and compared to the actual LBS of
spread of results further indicates the lack of interna- the ropes under review to demonstrate the reliability of
tional standards for the condition assessment of the algorithm.
corroded ropes. ➤ In the South African context, the researcher has seen
➤ The loss of metallic area (LMA) determined by the instances where the LMA traces indicated very little
various rope inspectors varied considerably. It must be signs of deterioration and the LF trace showed no
noted that the percentage LMA is a relative anomalies, yet the ropes had lost more than 35% of
measurement. It is usually a comparison of the their original breaking strength. The loss in these
measured metallic area (MA) in one section of the rope instances was due to very localized abrasion of the
(usually a ‘good’ section of rope where the instrument crown wires over a short section of the rope.
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The Journal of The South African Institute of Mining and Metallurgy NOVEMBER/DECEMBER 2000 443
How effective is the non-destructive examination
➤ It is therefore imperative to visually examine all determined by the inspector, between 9% and 45%,
indications of anomalies diligently and to combine the indicates that calibration procedures and measuring
results obtained by the visual examination, procedures are not adequate nor universal.
measurements and magnetic tests with the in-depth ➤ The wide variation in the methodologies of calculating
experience of the rope inspector. The researcher the loss in breaking strength (LBS) indicates a lack of
suggests that the ‘black box’ approach be avoided. consistency in the procedures and standards rope
➤ The South African Bureau of Standards Code of inspectors apply.
Practice 0293: 1996 ‘Condition assessment of steel ➤ Inspectors must be wary of implementing a ‘black box’
wire ropes on mine winders’ provides good guidelines approach, when assessing the condition of corroded
for establishing the condition of corroded ropes by ropes.
means of NDE, even though it is a time consuming ➤ The SABS 0293 guidelines for assessing the condition
process. of corroded ropes provide a good basis for rope NDE,
even though it is time consuming and laborious to
Assessment of the broken wire rope sample conform to these guidelines.
➤ Although the researcher attempted to choose the ‘best’ Broken wire rope sample
rope sample, with the least number of broken wires,
from the samples available for the experiment, the ➤ Magnetic rope test instruments are not able to identify
chosen rope still contained up to 24 broken wires/100 each wire break within multi-layer, low rotation ropes.
mm rope length at the worst spot. The 8 m section of ➤ The results indicate that instruments are not capable of
the rope sample, which was subjected to intense pin-pointing broken wires accurately, not even to the
analysis, contained 609 broken wires. The rope nearest 20 mm, along the axial length of the rope.
inspectors identified between 0 and 750 broken wires ➤ From the material presented by the rope inspectors it is
in the same 8 m rope sample applying NDE methods. obvious that it is not possible to ascertain the radial
It must be noted that the ropes from which the samples position of the broken wires within multi-layer, low
were cut were in service on a mine until discarded in rotation ropes.
terms of the discarded criteria available at that time ➤ Given the above, it must be concluded that it is not
(1993). The same discard criteria apply today. feasible to implement discard criteria for multi-layer,
➤ The large number of broken wires contained in the low rotation ropes based on the premise that the
rope made the examination and analysis of the rope accurate identification of the axial and radial position
condition more difficult than having fewer broken of wire breaks within the rope by means of magnetic
wires. NDE is possible.
The results of the experiment clearly indicate that the ➤ As stated in the conclusion to the literature search, a
rope inspectors were unable to identify each broken vast amount has been written about non-destructive
wire in the rope accurately. Two of the inspectors were rope testing and many successes have been claimed in
able to identify a large percentage of the broken wires. this field. Application of high-tech computerized
It must however, be noted that both these contractors systems are seen to be able to automate and deskill
were unable to identify the numerous clusters of rope NDE. The experiment conducted at Bochum,
broken wires situated around the 5200 mm mark. however, indicates that rope NDE in practice is not as
➤ The lack of response by rope inspectors to estimate the advanced as claimed in the literature.
remaining strength of a portion of the rope gives a
clear indication that inspectors are loath to derive General
remaining strength estimates for any ropes. Only one The researcher noted that the output signals from several
rope inspector calculated the LBS at between 4% and instruments were influenced by the speed and the direction
6%. Actual LBS was determined by destructive test to in which the test head travelled. This can influence the NDE
be 30,2%. results negatively.
Alternative instrument configurations
Acknowledgement
The results clearly indicate that the annular coil configuration
coupled with small airgaps improves the sensitivity of the The author would like to express his gratitude to SIMRAC for
instruments. This configuration is however impractical in the the financial support for this project, GAP503 and the
field. guidance received by the GAP(EAG) committee. He would
also like to thank the management of AATS for allowing him
Conclusions to prepare and submit this paper.

Corroded rope sample References

➤ The loss of breaking strength (LBS) values presented 1. SEMMELINK, A. Electromagnetic Testing of Winding Ropes—S.A. Institute of
by the various rope inspectors varied between 9% and Electrical Engineers, vol. 44, Part 5, May 1953.
50%. This clearly indicates the complexity inspectors 2. HARVEY, T. and KRUGER, H.W. The Theory and Practice of Electronic
Testing of Winding Ropes. Transactions of the S.A. Institute of Electrical
have to deal with when determining the LBS of Engineers. June 1959.
corroded ropes and the lack of standards. 3. KUUN, T.C. Low rotation winding ropes for long lift drum winders. Internal
➤ The large variation in the loss of metallic area (LMA) Anglo American of South African Limited document. May 1993. ◆
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444 NOVEMBER/DECEMBER 2000 The Journal of The South African Institute of Mining and Metallurgy