imca - sel023 - guidance on non-destructive examination (nde) by means of magnetic rope testing

Guidance onNon-Destructive Examination(NDE) by Means of MagneticRope Testing

IMCA SEL 023, IMCA M 197August 2009

International Marine

Contractors Association

www.imca-int.com

AB

AB

The International Marine Contractors Association (IMCA)

is the international trade association representing offshore,

marine and underwater engineering companies.

IMCA promotes improvements in quality, health, safety,

environmental and technical standards through the publication of

information notes, codes of practice and by other appropriate

means.

Members are self-regulating through the adoption of IMCA

guidelines as appropriate. They commit to act as responsible

members by following relevant guidelines and being willing to be

audited against compliance with them by their clients.

There are two core activities that relate to all members:

u Competence & Training

u Safety, Environment & Legislation

The Association is organised through four distinct divisions, each

covering a specific area of members’ interests: Diving, Marine,

Offshore Survey, Remote Systems & ROV.

There are also five regional sections which facilitate work on

issues affecting members in their local geographic area – Asia

Pacific, Central & South America, Europe & Africa, Middle East &

India and North America.

IMCA SEL 023, IMCA M 197

This guidance has been prepared for IMCA by a group under the

association’s Crane & Winch Operations Workgroup, reporting

to the Marine Division Management Committee and Safety,

Environment & Legislation (SEL) Committee.

www.imca-int.com/lifting

The information contained herein is given for guidance only and endeavours toreflect best industry practice. For the avoidance of doubt no legal liability shall

attach to any guidance and/or recommendation and/or statement herein contained.

© 2009 IMCA – International Marine Contractors Association

Guidance on Non-Destructive Examination (NDE)by Means of Magnetic Rope Testing

IMCA SEL 023, IMCA M 197 – August 2009

Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

3 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

4 Health and Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

5 Principles of Operation – How Magnetic Rope Testing (MRT) Works . . . . .11

6 Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

7 Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

8 Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

9 Competence and Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

10 NDE Trace Reports and Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

11 Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

12 Practical Pitfalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

13 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

IMCA SEL 023, IMCA M 197 1

Base trace The results of the first non-destructive examination carried out on the

wire rope. For best results, this NDE will be carried out early in the

wire rope’s life (before it suffers any damage in service), but does not

necessarily have to be carried out immediately after manufacture

Clearance gap (air gap) The gap between the inserts of the magnetic head and the test wire

rope

Event log A record of any events that occur during testing that may have an effect

on the final trace. For example: stopping and starting during test;

extraneous interference; weather conditions; any build-up of lubricant in

the magnetic head; etc

Fill factor The measure of the metallic cross-sectional area (MCSA) of a wire rope

in comparison with the circumscribed area given by the wire rope’s

nominal diameter (this is normally a constant for a given construction

and varies with different constructions)

Hall effect A conductor carrying a current in a magnetic field will develop a voltage

difference between its opposite sides (this is known as the ‘Hall voltage’)

Hall effect sensor A device which varies its output voltage in response to variations in a

magnetic field

Induced defect A known defect which has been intentionally introduced

Lay length The distance measured parallel to the centre line of a wire rope in

which an outer strand makes one complete spiral or turn around the

wire rope

Local fault (LF) A short anomaly in the wire rope, such as a wire break, cracked wire,

welded wire, corrosion pit or inter-strand nick

Loss of metallic area (LMA) A change in the amount of metallic material at a given position. Loss of

metallic area is normally associated with damage such as corrosion, wear

or mechanical damage

mV Millivolt – a unit of potential difference equal to one thousandth (10-3)

of a volt

Glossary of Terms

Magnetic flux A measurement of magnetism, measured across an area perpendicular to

the magnetic field

Magnetic head An assembly comprising powerful permanent magnets, sensors and a

distance measurement device that is fitted around the wire rope during

a magnetic rope test

Magnetic rope testing (MRT) The form of Non-destructive Examination most commonly used to assess

lengths of steel wire rope. During MRT, sections of the wire rope will be

progressively magnetically saturated by the relative movement of a magnet

along its length. Measurement of variations in the axial magnetic flux can

reveal the presence of variations or anomalies within the wire rope

Magnetic saturation The state reached when an increase in an external magnetic field cannot

further increase the level of magnetism within a material

Measurement span The length across which an instrument measures magnetic flux (i.e. the

length of an instrument’s sensing array)

Metallic cross-sectional area (MCSA) The sum of the metallic cross-sectional area of the individual wires

within the wire rope

Noise Spurious background information appearing on the trace

Non-destructive examination (NDE) A global term covering a range of techniques for assessing a component

for defects (internal and external) without causing significant damage to

that component

Resolution An instrument’s capacity to differentiate between multiple defects in

close proximity

Sensing coil A coil of fine wire, wound on a liner, capable of sensing and measuring

magnetic flux

Sensitivity A measure of an instrument’s ability to detect defects (i.e. the

smallest defect an instrument can detect)

Verification A means of ensuring that the machine is operating effectively

2 IMCA SEL 023, IMCA M 197


Magnetic rope testing (MRT) is a comparative process. It measures changes in magnetic flux along the length of

a wire rope and identifies the presence of anomalies in its structure. To fully assess the condition of a wire rope,

the operator of an instrument will need to know what to expect in terms of wire rope structure, fill factor and

metallic cross section.

Introduction

1


This document aims to provide guidance on the use of non-destructive examination (NDE) by means of MRT for

wire ropes, to assist with inspection and integrity management.

This document should be used as supplementary guidance to IMCA SEL 022/M 194 – Guidance on wire ropeintegrity management for vessels in the offshore industry – in which NDE is identified as one of the five tools which

can form part of a wire rope integrity management system. Where there are limiting factors to the use of NDE

equipment, IMCA SEL 022/M 194 gives further guidance.

2

Scope


This guidance has been produced as there is little other published guidance on MRT within the marine industry.

The development of the use of variations in magnetic fields to detect defects in steel wire rope started in the

early 1900s. Since that time there has been an improvement in the technology used. This particular method of

ascertaining the continuing integrity of steel wire ropes has been used in the mining and cableway industries for

many years. The most recent advances have been in the digital recording of data.

A magnetic material (such as a steel wire rope) in a magnetic field will become magnetised. The degree to which

the material has become magnetised is measured by the density of the magnetic flux within the material.

The magnetic flux is dependent on the strength of the magnetising field and the cross-section of the material

being magnetised. However, there is a limit to the maximum flux density within a material, that is, a point after

which it cannot become more magnetised, which is referred to as magnetic saturation.

MRT should be considered to be a supplement to visual examination and an aid to thorough examination. It will

identify areas in the steel wire rope in which defects may exist which will require further physical assessment.

Where there is a significant defect, suitable MRT will detect it. Its particular capabilities help offset the limitations

of visual examination, particularly on long lengths of wire rope (see ref. 2).

3

Background


In the majority of MRT systems, the magnetic head contains powerful permanent magnets. Potentially, this could

have an effect on safety:

u MRT equipment should only be transported in accordance with appropriate safety guidelines, as powerful

magnets can interfere with navigational equipment. The parameters described in publications such as the

current International Air Transport Association (IATA) Dangerous Goods Regulations or the current UK

Transport of Dangerous Goods Regulations (Civil Aviation Authority Document CAP 675 Section 12) should

be adequate;

u Powerful magnets may affect electrical, mechanical or magnetically encoded items such as laptop computers,

watches and credit cards and these should, therefore, be kept out of the vicinity of the magnetic head;

u All personnel should be aware that the powerful magnetic force will attract or be attracted to any ferrous

object and, therefore, the storage location and any movement of the magnetic heads needs to be planned

taking this into consideration;

u The magnetic head will have a powerful attraction to ferromagnetic metals. Care should be taken to avoid

trapping injuries, particularly when installing the head on a wire rope;

u Powerful magnets can affect the operation of medical equipment such as hearing aids and pacemakers.

The MRT may be carried out in a potentially hazardous marine environment. The operator should have a written

generic method statement and risk assessment. This should then be updated to address the specific on-site

conditions prior to operations commencing. This should, as a minimum:

u identify the location where the magnetic head would be installed;

u assess the risks, including manual handling;

u define exclusion zones and erect barriers;

u ensure the conduct of a toolbox talk prior to activities commencing.

Access to the wire rope under test may be difficult and may involve the operator working at height, in confined

spaces or in other hazardous conditions. This should be considered in the risk assessment and the appropriate

precautions taken.

The operators should have the correct personal protective equipment (PPE) for the task and environment in

which they are working.

During the wire rope examination, the wire rope and winding equipment will be in motion and will present

potential entanglement and/or crushing hazards:

4

Health and Safety


u It is likely that the moving machinery will be controlled from a position remote from the MRT operator.

It is essential that there is good communication between the test and machinery operators and that methods

of communication are agreed and understood by all parties prior to starting the test (see IMCA SEL

020/M193 – Guidance on operational communications: Part 2 – Lifting operations);

u The operator should ensure that the wire rope is not moving before installing or adjusting the magnetic

head;

u The operator should remain clear of moving wire rope and equipment and should set up the equipment in

a position of safety. Where a computer is utilised, its location should be sufficiently remote from the

magnetic head;

u Where the operation of the test is utilising the magnetic head in a static position, it is essential to suitably

secure the head;

u Any surface defects, protruding wires or accumulations of surface debris may cause the head to stick and

snatch.



During magnetic rope testing, the wire rope is moved through a magnetic head (normally containing powerful

permanent magnets) magnetising the wire rope to saturation. Any reduction in the metallic cross-section, such

as broken wires or material loss due to corrosion or wear, will cause a reduction in the magnetic flux within the

wire rope.

The principal defects within a wire rope are categorised as being either:

u loss of metallic area (LMA) – a change in the amount of metallic material at a given position. Loss of metallic

area is normally associated with damage such as corrosion, wear or mechanical damage; or

u local fault (LF) – a short discontinuity in the wire rope, such as a wire break, cracked wire, welded wire,

corrosion pit or inter-strand nicking.

The two types of defect will affect the magnetic flux differently and, therefore, will be measured differently. Loss

of metallic area will generally result in a gradual reduction in the magnetic flux over an area of the wire rope,

which can be measured directly. For local faults, the loss in metallic area and reduction in flux is likely to occur

over a very short length and in this case it is necessary to detect the flux leakage event as opposed to measuring

the reduction in the magnetic flux. LMA is, therefore, a quantitative measurement whereas LF is qualitative.

Variations in the magnetic flux can be detected by a number of methods, with the principal types of sensor being

measurement coils and Hall effect sensors. Sensors are mounted within the magnetic head. Different

instruments use different sensor configurations and may be set up to detect either LMA or LF or, in the case of

dual function instruments, both. The configuration and type of sensors used will determine an instrument’s

measurement span, sensitivity and resolution.

Detection of defects is generally accompanied by some method of distance measurement, often a rotating wheel

running along the surface of the wire rope (note the second bullet point in Section 12). This allows any defect

to be traced back to its position within the wire rope, for subsequent investigation.

Signals from the sensors are processed (amplified and filtered to remove extraneous ‘noise’) to facilitate

interpretation. Verification (see Section 7) of the instrument, prior to inspecting a wire rope, will allow the

operator to equate these changes in magnetic flux with changes in metallic cross-section.

5Principles of Operation –How Magnetic Rope Testing (MRT)Works


This part of the guidance is aimed at the factors which should be addressed in order to minimise the potential

for misinterpretation:

u Sensitivity – Whilst it is not always practical to use the same machine, or the same model of machine,

consideration should be given to their comparative sensitivity levels. If a different machine is used, all

personnel involved should be made aware of its sensitivity level and its implication (if any) for comparisons.

Although not critical in respect of major defects, lower sensitivity machines may not reveal the more minor

indications that a higher sensitivity machine will show. Sensitivity is a machine characteristic and is not

variable by the operator;

u Speed limits and speed variability – All machines have upper and lower speed limits within which accurate

results can be obtained. Ancillary items of equipment (such as winches) need to be able to be operated

within the speed range of the NDE equipment being used. There is a need to be aware that some machines

are sensitive to speed variability, which may affect the consistency of the result;

u Resolution – Consistency of resolution is an important aspect. High resolution capability will assist the

process of identifying close proximity defects and, therefore, should be considered in the selection process.

This is a machine characteristic;

u Gain – Increasing gain will provide a more prominent pictorial indication of a defect and should be set by

the operator prior to commencing the trace. Gain should not be altered whilst a trace is being taken (see

Section 7). However, when comparing traces with different gain settings, it would be necessary for the

competent person to take the effect of the gain settings into account during interpretation.

6

Parameters


Prior to use, it is necessary for the machine to be verified for each wire rope diameter and construction in

accordance with the manufacturers’ instructions. To verify the extent of the LMA the metallic cross-sectional

area (MCSA) it will be necessary to know the wire rope construction. The MCSA or the fill factor may be

obtained from the wire rope manufacturer for the specific wire rope construction and diameter. To verify for

LF, a function check is required. One method of conducting this is to attach a short test wire representing a

known percentage of the MCSA to the exterior of the wire rope and measure the ‘induced defect’.

7

Verification


The application of the NDE process as described in this document should be as a result of assessment taking

into account the likely deterioration modes induced by particular use. This assessment should identify the

following:

u Wire ropes which should be subject to NDE;

u The extent (length) which should be subjected to the process taking into account past, current and future

usage;

u The periods/frequency at which the process should be applied. Where NDE is elected for use it may be

carried out at a frequency of at least once per year, but the frequency and extent may be increased as a result

of the previous findings and usage;

u Any specific usage, such as prolonged heave compensation, which could cause internal damage to the wire

rope, may require an increased frequency of NDE.

Ideally, a pre-use NDE base trace should be taken at the installation of the wire rope onto the deployment system

at site. This will provide a base trace which includes any background influence on the trace. In circumstances

where this cannot be done or is impracticable, an NDE trace should be carried out at the earliest opportunity.

It should be borne in mind that the process may prove of value to detect defects even in circumstances where

significant use has occurred or where the wire rope may contain a significant defect prior to the base trace being

carried out.

8

Procedures


It is necessary for the NDE to be supervised by a competent person.

It is necessary for the operator carrying out the NDE to be trained in both visual wire rope inspection and the

use of NDE techniques, and to have the required knowledge, skill and experience.

The operator should be trained on the machine that is expected to be used, taking into account the

manufacturer’s instructions.

The operator should be aware of the following aspects:

u Equipment transport and storage including ‘dangerous goods by air’ and ‘dangerous goods by sea’

requirements;

u Equipment limitations, e.g. wire rope diameter, construction and test speed;

u Equipment setup and verification;

u Awareness of wire rope travel direction in relation to the magnetic head;

u Troubleshooting and practical pitfalls;

u Effect of weather conditions on the test;

u Effect of local interference, e.g. electrical machinery, radio signals, etc.;

u Effect of the fleet angle of the wire rope through the magnetic head;

u Effect of the wire rope surging through the magnetic head;

u Effect of loss of air gap in the magnetic head;

u Anomalies which may be caused by extraneous factors, such as metallic contamination;

u The difference between a minor and a significant indication on the trace.

9

Competence and Training


An integral and essential part of all NDE is thorough reporting and record keeping.

The following items should be recorded at the time of test:

u Date of test, wire rope identification and certificate;

u Wire rope history and likely future service – history is of particular relevance especially if, for example, the

wire rope has been refitted ‘end-for-end’ (with the ends reversed); future use could be relevant if the service

conditions of the wire rope are about to change, e.g. to working in deeper water;

u Length of the section of wire rope inspected;

u Manufacturer and model and serial number of magnetic head:

– sensitivity

– speed limits and speed variability

– resolution

– gain;

u Direction of travel of wire rope relative to magnetic head;

u Details of head inserts and liners (if not dedicated magnetic head);

u Verification settings;

u Event log – e.g. stopping and starting during test, extraneous interference, weather conditions, any build up

of lubricant in the magnetic head;

u Sight of previous reports and traces;

u Name of operator.

The trace results need to be interpreted by a competent person. Visual inspection of the wire rope is essential

when interpreting an anomaly in the NDE trace.

The trace record can be electronic and may be e-mailed onshore, which will facilitate additional support and

detailed interpretation if required.

The results can be used to determine the frequency of further inspections.

10

Reports and Interpretation


The system and format for the recording and retention of records should be considered and confirmed prior to

initiating magnetic rope testing. A standard format should be used across the entire fleet to facilitate

comparisons between traces for each individual wire rope and to compare traces for similar wire ropes

throughout the fleet and wire ropes in storage.

Consideration should be given to having a backup copy of all data held in a secure location.

Records should be retained by the owner/operator of the wire rope for the life of the wire rope as a minimum.

However, consideration should be given to maintaining post-disposal records of the wire rope to provide

research data for future use.

Data which should be recorded and retained is detailed below:

u The unique identity of the wire rope

– The manufacturer’s number plus any differentiators for multiple lengths cut from a single drum/

production run

– If intermediaries have applied different identity numbers these should also be recorded and a cross-

reference document maintained;

u The manufacturer’s test (mill) certificate and if necessary a supplementary record containing:

– Fill factor

– Lay length

– Comprehensive description of the construction;

u Wire rope integrity management records (see ref. 2) including:

– Inspection and thorough examination records

– Periodic dimensional measurements

– Original and current length record, including the dates of cutbacks, length of cutbacks, reasons for

cutbacks and confirmation of the end from which the cutback was taken

– Whether the wire rope has been reversed end-for-end

– Lubrication records

– Location of all visible broken wires which have been trimmed back/made safe;

u Wire rope history:

– Installation date

– Loading history – as a minimum, the number of hours the wire rope has been utilised in heave

compensation;

11

Records

u Test execution:

– The identity, competency and training records of the operator

– The identity of the machine being used to conduct the test – make, model and serial number

– Each time the machine is used a verification check should be undertaken and recorded prior to the

examination of the wire rope. These records are to be retained with the trace of the wire rope which

has been subject to the MRT

– Date of trace being taken

– Weather conditions

– Machine settings records, including the gain setting and whether the gain has been altered at any time

during the test run

– Whether the test run was completed without any halts and if halts made at what point and for how

long

– The length of the wire rope examined and the start point

– The speed at which the trace was taken

– The direction in which the trace was taken (e.g. from drum end or from wet end)

– All data related to what the operator considered a false indication, e.g. build-up of grease, swarf found

and location, etc.;

u The findings of the analysis of the individual trace and any actions resulting from the analysis, e.g. dimensional

checks;

u All base traces and previous reports and traces should be retained for the life of the wire rope.



An operator should be aware of the situations and/or conditions which may occur at the site of an examination

and which could potentially complicate interpretation of the results, but may not necessarily invalidate the test.

These may include:

u Heavy lubrication – In some cases lubricant may cause slippage in the distance measurement system. Errors

in distance measurement will make it impossible to determine the position of a defect along the length of

the wire rope, preventing further examination;

u The distance measurement system should be monitored to verify that it continues to operate. If the

equipment on which the wire rope is installed has a line-out meter, this can be used to confirm the accuracy

of the distance measurement;

u Metallic contamination – Metallic (ferrous) contaminants on the surface of the wire rope will increase the

noise trace and create anomalous indications. Larger pieces of debris could cause damage to the machine

and excessive lubricant can hold metallic contaminants;

u External interference – The presence of powerful magnetic sources, large pieces of ferromagnetic material

or radio transmitters, close to the magnetic head may affect the trace. If there is relative movement between

the magnetic head and the source of the interference then its effect will be variable and potentially significant;

u Rope/head movement – A magnetic head is designed to accommodate a range of wire rope sizes and to

minimise movement, inserts are fitted suitable for the size of wire rope under test. If inappropriate inserts

are used or there is a lot of lateral movement within the wire rope, then this may result in noise and/or

spurious indications on the trace;

u Fleeting – Changes in the fleet angle during the test can result in unpredictable movement of the wire rope

through the magnetic head, resulting in lateral movement of the wire rope in the head (see above);

u Surging – Where the wire rope is wound between two winches, speed variations can result in unpredictable

movement of the wire rope through the magnetic head. This can result in lateral movement of the wire rope

in the head (see above) or the NDE system operating outside its speed envelope;

u Continuity of examination – The configuration of the wire rope and access restrictions may prevent the wire

rope being examined in a single uninterrupted test. The operator should ensure that part tests are correctly

reassembled to provide a single trace that accurately identifies the position of any defects.

A competent operator who is aware of likely conditions in the field should have no difficulty differentiating

between real and spurious indications.

12

Practical Pitfalls


1 Safe use of lifting equipment. Lifting Operations and Lifting Equipment Regulations 1998. Approved Code of Practice – L113 HSE Books 1998 ISBN 0 7816 1628 2

2 Guidance on wire rope integrity management for vessels in the offshore industry – IMCA SEL 022/M 194, 2008

3 Guidelines for lifting operations – IMCA SEL 019/M 187, 2007

4 ASTM E1571-06: Standard practice for electromagnetic inspection of steel wire ropes – American Society for

Testing of Materials 2006

5 Wire Rope Non Destructive Testing – Survey of Instrument Manufacturers – HSE Offshore Technology Report

OTO 2000 064 2000

6 SANS 10293:1996 (SABS 0293) Condition assessment of steel wire ropes in mine winders – Standards

South Africa 1996 ISBN 0 626 10929 9

7 SANS 10369:2007 Non-destructive examination and testing of steel wire rope – Standards South Africa 2007

8 BS ISO 4309: 2004 Cranes – Wire Ropes – Care, maintenance, installation, examination and discard – BSI 2004

ISBN 0 580 44558 5

9 Guidance on the installation, maintenance and use of steel wire ropes in vertical mine shafts – Deep Mined

Coal Industry Advisory Committee (DMCIAC) via HSE website (www.hse.gov.uk)

10 BS EN 12927-8: 2004 Safety requirements for cableway installations designed to carry persons – Ropes – Part 8: Magnetic rope testing (MRT) – BSI 2004 ISBN 0 580 44661 1

11 The IATA Dangerous Goods Regulations manual 2009

12 UK Transport of Dangerous Goods Regulations (Civil Aviation Authority Document CAP 675 Section 12)

13

References

imca - sel023 - guidance on non-destructive examination (nde) by means of magnetic rope testing

Documents

magnetic rope testingimca

magnetic field

magnetic head etcfill

environment legislation

magneticrope testingimca

test wire ropeevent

wire ropes life

circumscribed area