A Discussion of Wire Rope Inspection Methods and Instrumentation

2. Welcome to this
PowerPoint Presentation
on our
Magnetic Rope Testing (MRT) Technology
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3. In the following, we will demonstrate
1. that our MRT Systems are Linear and
2. that any rope deterioration can be modeled, with any desired degree of accuracy, as the sum of properly sized and spaced Step Changes.
Therefore,
3. test results from our MRT systems can be represented as the corresponding sum of Step Responses.
Those familiar with the concepts of Linearity, Linear Superposition, and Linear Transformation will immediately associate them with the
equation, f(x+y) = f(x) + f(y).
In layman’s terms and on a practical level: A process is linear if, when you double the input, you will double the output.
For example, consider the operation of a flour mill: Assume you double the “wheat input,” then, obviously, you will also double the “wheat
flour output.” This simply means that the flour mill is a linear system.
In the following, we will present additional examples to further illustrate the concepts of linearity.
Step Input (or Step Change) and Step Response. The concepts of “Step Change” and “Step Response” can be immediately explained in terms of
a steel wire (or rod) that is attached to a wire rope. Then, the added wire represents a “Step Change” of the overall rope metallic cross-
sectional area (CSA). Then, the resultant signal traces, produced by an MRT system, are the corresponding “Step Responses.”
This presentation will show that our MRT Systems are linear. Here, the rope condition (i.e., various types of rope deterioration) is the MRT
system input, and the test signals (or chart traces) are the outputs of our linear MRT systems. By way of example, step changes of wire rope
cross-sectional metallic area (CSA) (produced by short pieces of steel wires attached to the rope) are used to simulate system inputs, with the
corresponding step responses as outputs. As an aside, broken or missing wires also cause step changes of rope CSA.
Demystifying MRT Chart Interpretation
There is a general lack of knowledge of MRT and an unwillingness to use it – even among
otherwise experienced wire rope professionals. Entire operations are jeopardized by a
sometimes perplexing and irrational reluctance to use proper inspection procedures.
This presentation is intended to untangle some of the complexities that hamper reliable wire
rope nondestructive examinations (NDE), which will be done by using two basic concepts that
have been extensively used – for example – in control systems engineering.
They are the notions of
1. Linear Systems, and
2. Step Input (or Step Change) and Step Response.
Here, it is important to realize that our MRT Systems are Linear Systems. This means that
changes of the rope metallic cross-sectional area (CSA) can be represented with any desired
accuracy as the sum of properly sized and spaced Step Changes of CSA, and that the LMA and LF
chart signals are simply the sum of the corresponding Step Responses.
The above sounds much more complicated than it is. Actually, these ideas are quite intuitive.
The following easy-to-understand examples will completely explain the basic concepts. We hope
that you will find them straightforward and even entertaining.
Complete Wire Rope Nondestructive Examination (NDE):
Visual and Magnetic Rope Testing (MRT)
Modern wire ropes (including multistrand and IWRC ropes) deteriorate internally with no
externally visible signs. This situation clearly calls for MRT.
Conversely, visual inspections are indispensable for rope sections that are not accessible by MRT
(for example, near end terminations and on compensating sheaves).
MRT and visual inspections complement each other and should be combined.
A complete wire rope inspection consists of several components. This means, a thorough
inspection must consider all aspects of a rope's condition, including:
a. the results of an MRT rope inspection,
b. the findings of a visual inspection,
c. the rope construction,
d. the rope's operating conditions and related damage mechanisms,
e. the history of the rope under test and that of its predecessors.
In other words,
• the inspector should use all inspection methods available to him, and
• he should know in advance what type of rope deterioration he can expect to find.
Prologue
Rope wearing out and breaking is an old problem that is still bringing down today’s gigantic and
hugely expensive loads. Only now, it is much harder to locate worn rope, for example in 2000
feet of reeving tackle and looking for it 200 feet up in the air.
On top of that, modern ropes deteriorate inside, so sole visual inspections are out of the
question. In addition, most wire ropes are covered with grease, which makes visual inspection
unfeasible -- even for surface deterioration.
There are a great many modes of wire rope deterioration such as external and internal broken
wires, mostly in clusters, valley breaks, corrosion including corrosion pitting, IWRC core
deterioration, total core failures, bird caging, kinks, etc. This situation is complex. It makes visual
inspections unreliable.
For example, consider IWRC ropes. They typically deteriorate internally, starting with core
degradation and, eventually, total core failure. Deterioration then progresses to so-called valley
breaks – a very serious warning sign of imminent rope failure. Failures of IWRC ropes are usually
unexpected without any advance visual indications.
As an illustration of the above, please consider the pictures on the right. For additional details,
please click on each of the images to follow the links.
Click to Proceed

4. Basic Examples
Linear Systems
Linearity
Linear Superposition
Linear Transformation

5. Linear Superposition
Rotational Motion
Translational Motion
This slide illustrates the linear superposition of
two motions. The movement of the soccer ball can
be described as a combination of two separate
motions:
translation without rotation, and rotation without
translation.
Please click on the green icon to start the
translation, and on the blue icon to start the
rotation. Click on the respective icons again to
start and stop each motion.

6. Transformation
Transformation
Transformation
Linear
Transformation
Linear
Superposition
Coin-to-Candy
Transformation Machine
Proceed

7. MRT System
MRT
System
Input
(Rope
Condition)
MRT System Output
(Test Signals)

8. Step Changes of CSA
Step Response LMA Signal
Step Response LF Signal

9. Sensor Head
LMA & LF
Sensors
LMA Signal
LF Signal
Step
Discontinuities
Rope Under
Test (RUT)
Display
Screen
Forward
Reverse

10. 200%
100%
0
150%
50%
100%
0
50%
200%
100%
0
150%
50%
200%
100%
0
150%
50%
CSA = 100%
CSA = 25%
Total CSA = 200%
Total CSA = 200%
Total CSA = 125%
Total CSA = 75%
Wire Rope Roughness (WRR), a
new indicator for the quantitative
characterization of wire rope
deterioration
Click here for
instructions
Proceed

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17. Click here for
instructions
Standard
ASTM E 1571
Echoes
Proceed

18. Echoes
3 Missing Wires
2 Missing Wires
LMA Signal
LF Signal

19. Echoes
LMA Signal
LF Signal

20. Wire Rope Cross-Sectional Area (CSA) Changes,
Step Change Approximations, and
Linear Superposition
Any Change of Metallic Cross-Sectional Area (CSA)
can be represented – with any desired degree of
accuracy – as the sum of Step Changes.
Then the LMA and LF Signals caused by this Change
of CSA can be approximately represented as the
sum of the corresponding Step Responses.

21. Rope Cross-Sectional Area
Step-Change Approximation
Step Response
Rope Cross-Sectional Area

22. Rope Cross-Sectional Area
Step-Change Approximation
Step Response
Rope Cross-Sectional Area

23. Epilogue.
Consider the job of an auto mechanic. It has become increasingly specialized in the 21st century. Until the 1960s, all
you needed was a set of wrenches, screw drivers, a strong pair of pliers, and you could repair most cars. Modern
cars are much more evolved, with hundreds of computer chips. Specialized equipment is required to diagnose
problems with these sophisticated electronic devices, and auto mechanics today must learn how to use modern
electronic diagnostic equipment as well as all the traditional tools of the trade.
***
Similarly, consider the job of a wire rope inspector. Even all the way into the 20th century, everything he needed was
some rags, a marlin spike, calipers, a pair of pliers, flashlight, cleaning fluid, and, maybe, some cash register paper
together with wax crayons. These tools were sufficient for the visual inspection of simple ropes, typically with a fiber
core.
In contrast, modern wire ropes (including multistrand and IWRC ropes) are much more complex. They will inevitably
deteriorate inside with no visible indications. So, sole visual inspections are out of the question. In addition, most
wire ropes are covered with grease, which makes visual inspection unfeasible – even for surface deterioration.
Specialized MRT equipment is required to diagnose problems with these sophisticated modern wire ropes, and
inspectors today must learn how to use advanced electronic MRT diagnostic equipment as well as all the traditional
tools of the trade.

24. Visual Wire Rope Inspection Methods: Past and Present
Here is a short discourse of visual inspection methods.
• The "rag-and-visual" method can be used to check for external damage. Grab the slowly moving rope lightly with a rag or
cotton cloth. Broken wires will often "porcupine" (stick out) and these broken wires will snag on the rag. If the cloth catches, stop
and visually assess the rope.
Paradoxically and completely irrationally, the elevator industry has refused to use preformed wire ropes, at least until the 1980s,
for no other reason than the fact that broken wires will not porcupine and, therefore, the rag-and-visual method becomes
ineffective. Please note that preforming is universally used because it offers many advantages.
Caution: The rag-and-visual” method is very dangerous and has caused serious accidents in the past. Sarcastically, this
approach has also been called the “bloody-hand” method.
• If broken wires do not porcupine, another test must be implemented. The inspector will move along the rope in two to three feet
segments while examining each section. This method becomes tedious and very cumbersome for the inspector if cables are well
lubricated with grease and must be cleaned for the inspection.
• Another visual inspection method is to measure the rope diameter with a caliper. Compare the rope diameter measurements with
the original diameter. If the measurements are different, this change indicates external and/or internal rope damage.
• Visually check for abrasions, corrosion, pitting, and lubrication inside the rope. Insert a marlin spike beneath two strands and
rotate to lift strands and open the rope.
For simple fiber-core ropes, visual inspections can be effective because all wires will eventually become externally visible along
their length. However, this is not the case for modern ropes that deteriorate internally with no visible indications.

25. Safety
Critical
Mission
Critical
Single
Points of
Failure
Wire
Rope
A safety-critical system or life-critical system is a
system whose failure or malfunction may result in one
(or more) of the following outcomes:
• death or serious injury to people
• loss or severe damage to
equipment/property
• environmental harm
A single point of failure (SPOF) is a
part of a system that, if it fails, will stop
the entire system from working.
Mission critical .systems or business critical
systems are defined as systems whose failure
will cause extreme losses for a business.
The Importance of Wire Ropes
The Importance of Wire Ropes cannot be overemphasized. For any operation that uses wire ropes, they are safety critical as well as single
points of failure. Consequently, they are also mission critical.

26. The Responsibilities of a Wire Rope Inspector
Failures of high-value offshore and other ropes – which are safety critical, single points of failure and mission
critical – are unacceptable. Besides loss of life, they can cause and have caused catastrophic losses in the seven,
eight, and even nine figure range.
These huge losses can significantly affect the bottom line and the reputation of even major corporations. They should
and will eventually draw the attention of upper management
Despite their mission critical importance, wire ropes are frequently considered low-tech commodities without much
interest. Failures are frequently considered and accepted as “inevitable.”
While appropriate rope inspection methods, discard criteria and maintenance procedures are available, they are
frequently not applied. Entire operations are jeopardized by an unexplained and sometimes perplexing reluctance to
use proper wire rope safety procedures. Traditional preventative maintenance and replacement schedules – if
followed at all – typically are based on some form of in-service visual inspection and, maybe, MRT inspections often
with instruments of dubious performance by inspectors with questionable skills, combined with a large amount of
educated or blind guesswork.
Considering the above, wire rope users and inspectors have an obligation to use all available inspection methods –
including MRT – for their wire Rope Nondestructive Examinations (NDE). Sole visual inspections must be considered
inadequate and even negligent.

27. NDT Technologies
At NDT Technologies, we have 41 years of R&D and practical experience with all aspects of wire rope Nondestructive
Examination (NDE). Our MRT instrumentation, hardware and software, was developed by highly qualified electrical,
signal processing, and instrumentation engineers.
The performance of our MRT instrumentation is unmatched. In contrast to any of our competitors, we offer high-
fidelity and completely noise-free signals that are quantitative and, therefore, can be used for making reliable rope
retirement decisions.
Our MRT instrumentation was extensively evaluated by impartial government and semi-government agencies in
various Round Robin tests. For information on these and other validation trials, please click on the link to openand
peruse these “Reports on Validation Trials.”
Buyer beware: With much dubious MRT equipment on the market, users are well advised to use due diligence and
to be careful when making purchase decisions. Manufacturers claims are often unsubstantiated and should be
viewed with considerable suspicion.
As demonstrated by this presentation, an easy do-it-yourself first test for the comparison of competing MRT devices
is to evaluate their step responses. Simply push-pulling a steel rod through a sensor head and observing the step
response is a simple experiment. Of course, there are many additional questions to ask, such as IP ratings of the
equipment, inspection accuracy, rationality of signal interpretation, ease of handling, etc.

28. Thank you
Herbert Weischedel
herb.weischedel@ndttech.com
Wire ropes are critical system components, wherever they are used.
Their importance cannot be overemphasized.
This presentation tried to take some of the mystery out of MRT inspection and
chart interpretation by explaining some of the basic underlying principles. .