Performance Validation of Permanently Installed Guided Wave Tools
on Inaccessible Pipelines and Cased Crossings
GROUP SPONSORED
PROJECT OUTLINE
PR 21889
April 2013
Summary
This project is concerned with the implementation of improved methods for
assessing the condition of difficult-to-access sections of high pressure pipelines
in order to facilitate an Integrity Management Program. This situation primarily
arises for gas transmission and distribution pipelines which are not suitable for
internal in-line inspection (ILI) tools, so-called ‘unpiggable’ pipelines. Of
particular concern are cased crossings of roads, railways and rivers, where the
external casing prevents direct access to the surface of the carrier pipe for
direct assessment, even if it is excavated.
The aim is to use enhanced ultrasonic guided wave procedures to ensure full
coverage of the cased section and to apply signal analysis processes to allow
the size of degradation detected to be determined, so that an integrity
assessment may be applied. This situation is particularly acute in the USA
where the [US] Pipeline Safety and Improvement Act of 2002 requires
operators to implement an Integrity Management Program for cased crossings
in High Consequence Areas.
Of particular significance is the use of permanently installed sensors linked with
time-dependent monitoring to ensure that small increments of change in the
condition of the pipeline may be detected to determine if the pipe condition is
stable or if it is degrading through, for example, corrosion.
TWI has been in the forefront of guided wave developments for more than 20
years and has implemented novel features for guided wave testing evaluated
through such bodies as OPS, PRCI and NYSEARCH. Recent developments in
both pulse-echo and through-transmission testing, and also in signal analysis,
have been incorporated into a real-time monitoring system which will be
evaluated under field conditions for pipeline assessment. The outcome of this
work will be performance data which will provide pipeline operators with the
confidence to use information from guided wave monitoring as part of their
Integrity Management Program.
TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, UK. Tel: +44 (0)1223 899000
Performance Validation of Permanently Installed Guided Wave Tools
on Inaccessible Pipelines and Cased Crossings
Project Concept
The determination of the condition of high pressure pipelines which are not suitable for internal in-line
inspection (ILI) is problematic. Such transmission and distribution lines tend to be buried and have protective
coatings which make them inaccessible for easy external inspection access. This is particularly relevant for gas
lines. The situation is most significant for sections where the pipeline crosses roads, railways or rivers, where a
protective casing is present around the pipe for the length of the crossing. For these sections the outside of the
pipe is inaccessible for direct assessment, even when it is excavated, and the costs of exposing the ends of the
crossing may be excessive. Consequently, there is a need for a method of determining the condition/integrity of
such pipelines in general and that of cased crossings in particular.
Pipeline operators in the USA are particularly affected by this as they have to comply with legislation which
governs gas pipelines. The PHMSA Guidelines for Integrity Assessment of Cased Pipe for Gas Transmission
Pipelines in HCAs, published in March 2010(1), state that: ‘By Act of [US] Congress, the Pipeline Safety
Improvement Act of 2002 (as implemented by 49 CFR 192, Subpart O) mandates that all gas transmission pipe
in high consequence areas have a baseline integrity assessment and a reassessment using specified methods at
least once every 7 years, unless a waiver is granted.’
These guidelines state that where it is not possible to gather sufficient information to determine the integrity of
the cased section, excavations and direct examinations are required (unless a hydrotest is performed). Further,
the Guidelines state that long range ultrasonic testing using guided waves (GWUT or GWT) is the only ‘Other
Technology’ which may be used to provide information about the condition of cased crossings where ILI cannot
be applied. However, it is also stated that, for GWT to be accepted as a valid means of Direct Assessment of
such pipelines, 100% coverage of the length of the cased section has to be achieved. It is clear that there is
considerable benefit for the pipeline operator in using guided wave testing to reduce the number of cased
sections which are required to be excavated. However, for this approach to be acceptable to PHMSA there must
be some assurance that the required 100% coverage can be attained. Of particular significance is the rate of
attenuation (loss) of the ultrasonic energy caused by the presence of coatings on the carrier pipe, plus the
effects of end seals and centering spacers within the casing. This limits the valid test distance attainable, even
when testing from each end of the casing, such that the 100% coverage is difficult to achieve. Enhancements to
the guided wave test performance are therefore required such that full coverage can be assured in the majority
of cases. Further, the guided wave tests currently do not provide results which can be used directly as inputs to
an integrity assessment using procedures such as ASME B31-G or RSTRENG. There is a need to obtain more
quantitative information about the size and location of discontinuities so that their severity may be assessed.
This project addresses these issues and is based on the successful implementation of ultrasonic guided wave
technology for cased crossing evaluation in earlier DoT funded work(2, 3) and a novel technique for flaw sizing
using guided waves being developed with support of the pipeline industry(4). The project will be carried out by
TWI, a key player in the development of guided wave testing for pipes since its inception and through its
subsidiary, Plant Integrity Ltd, which supplies guided wave test equipment and services. Two vital elements
related to inspection of cased crossings will be studied, namely assurance of the complete coverage of the
crossing from the accessible ends and generation of relevant information about anomalies and flaws in the
crossing so that recognized fitness for purpose standards may be applied. This is achieved by using an
automated monitoring approach with permanently installed sensors. The project brings together developments
carried out by TWI on flaw sizing using guided waves, procedure enhancement for coated pipelines and
automation of long-term monitoring techniques. This has several important advantages:

Repeated monitoring using permanent sensors allows complex, but constant, responses from features
in the crossing – end seals, centering spacers, welds and other appurtenances – to be calibrated out
and only changes in condition detected,

The RATE of change of condition may be determined, thereby leading to prioritisation of remedial
actions by the operator among many inaccessible regions,

Quantitative assessment of flaw size allows engineering assessments to be made about pipeline
condition, satisfying the legislative requirements of an Integrity Management Program.
The aim of the project is to validate the performance of the long-term monitoring & surveillance system for
detection and evaluation of time-dependent degradation in pipelines, with special reference to cased road
crossings. A key element will be to bring the findings to the attention of the relevant authorities, notably US
DoT/PHMSA in order to gain approval for the use of such methods to avoid alternative requirements, such as
hydrotest and to update current guidelines for guided wave examination (5).
TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, UK. Tel: +44 (0)1223 899000
Performance Validation of Permanently Installed Guided Wave Tools
on Inaccessible Pipelines and Cased Crossings
Objectives
The overall objective of this project is to provide pipeline operators with data to define the performance of an
integrated ultrasonic guided wave monitoring system, using permanently installed sensors, for determining the
condition of inaccessible lengths of pipeline, with special reference to cased crossings.
The specific objectives are:

Demonstration of the ability of the system to achieve full coverage of pipeline/cased sections. The
crossing lengths to be studied and pipeline diameters and thicknesses will be determined by the funding
partners in the project, but these will be of sizes relevant to the gas transmission and distribution
industries.

Determination of system stability for long term monitoring and hence establish the limit of sensitivity
for detection of pipeline flaws.

Demonstration of the capability to determine the presence of flaws under field conditions.

Demonstration of the capability to establish the growth of time-dependent degradation, such as
corrosion, over the monitoring period.

Demonstration of the capability of the system to quantify the size of flaws detected so that an Integrity
Management Program may be implemented.

Presentation of the results/evidence of performance to the relevant regulatory bodies.
Benefits
The main outcomes of the project are:

The availability of data to support the application of non-invasive technology for in-service monitoring
of the Cased crossings. Such data are required for both internal justification by the operators for the
use of this technique and as evidence to support cases to regulatory bodies for its application.

The subsequent provision of a service by TWI and its Affiliates which will allow this technology to be
available to industry. Sponsors of the project will receive a discount on services provided by TWI or its
Affiliates.
The use of permanent monitoring will allow:

Direct inspection intervals to be extended with minimal degradation and quantitative information about
the condition of the pipe that can be input into FFS calculations.

Identification and prioritisation of crossings that require action for examination and repair.
The long-term benefits to Project Sponsors of the application of non-invasive technology are:

Savings in the indirect consequential costs of both inspecting these lines and for hydrotesting.

Improved knowledge based long-term planning and minimisation of disruption to management
operations.

Reduction in the likelihood of leaks occurring in these pipelines and associated environmental
contamination, through prioritisation.

Reduced risk of catastrophic failure, fire and explosion.

Demonstration of added safety in high population or environmentally critical areas.

Demonstration of added diligence on older pipelines reaching thickness limits.

Continuous information on pipe
management.
Copyright © TWI Ltd 2013
condition to
enable
better risk, integrity, and
maintenance
Performance Validation of Permanently Installed Guided Wave Tools
on Inaccessible Pipelines and Cased Crossings
Approach
The work will consist of instrumenting representative pipe sections with TWI’s novel guided wave monitoring
tooling and carrying out long-term data gathering exercises using enhanced procedures developed for this
purpose. The study will assess the performance attained for evaluation of time-dependent degradation and
quantify the accuracy of the method. Owing to the inaccessibility of the carrier pipe in cased crossings it is
envisaged that most of the work will be carried out on single pipes which are accessible for follow up by other
NDT methods. These will be a) full size specimens set up at TWI for detailed evaluation, b) Accessible pipes at
sites of funding partners, particularly those pipes where there is an actual corrosion issue that may be
monitored. However, if any partner has a cased section which is likely to be excavated or removed from service
within the duration of the project, such a crossing could also be monitored. The main areas of study are:

System stability – This influences the ultimate sensitivity of the system,

Capability for detection of time-dependent degradation (principally corrosion), in conjunction with flaw
assessment by other NDT methods,

Performance for flaw size determination.
This will be carried out both at TWI and at selected sites, agreed with the project sponsors.
Representative cased crossings will be manufactured at TWI and corrosion (real and simulated) induced to
replicate what happens in industry. The pipe sizes, lengths, coating types etc will be agreed with the sponsors.
The performance from the monitoring system may therefore be determined. In addition:

For field installations TWI will provide the equipment for the monitoring exercise and will install and
maintain it on the sponsor’s facilities. TWI will gather data and will store, analyse and interpret it.
Feedback will be given to Sponsors as to the intermediate interpretation of the data.

TWI will prepare regular condition reports on the basis of the monitoring data, which will be the basis of
comparison with any other examinations carried out.

TWI will provide the results from the representative corroded cased crossings at TWI.

On presentation of the results of the other examinations, TWI will compare these with any condition
reports from the monitoring exercise and prepare a performance report.

On completion of all the comparison exercises, a final report will be produced on the overall
performance attained by the monitoring system. This will include an assessment of the system’s
effectiveness and recommendations for industrial use of the method.
The expectation is that project participants will:

Make sections of pipe available for this monitoring exercise and facilitate access by TWI for the
installation, operation and maintenance of the monitoring systems.

Make available the results from any examinations carried out on the crossings being monitored for the
purposes of comparison with the monitoring data.
In parallel with this, technique development will continue at TWI within the project in order to improve the
signal processing and data interpretation methods so that the ability of the non-invasive technique to evaluate
cased crossings will be based on state-of-the-art methods.
Deliverables
The principal deliverable will be a body of evidence to demonstrate the performance of permanent monitoring
tools and procedures for cased crossings and other inaccessible lines. These will be presented in:

Periodic reports of the performance of the monitoring systems and the initial interpretation of the
interim monitoring data.

A final report detailing the performance achieved by the monitoring system in comparison with standard
methods of determining condition and recommendations for industrial application.
TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, UK. Tel: +44 (0)1223 899000
Performance Validation of Permanently Installed Guided Wave Tools
on Inaccessible Pipelines and Cased Crossings
References
1. ‘Guidelines for integrity assessment of cased pipe for gas transmission pipelines in high consequence areas
(HCAs)’, Revision 0, publ. PHMSA, March 1, 2010. http://primis.phmsa.gov/gasimp/documents.htm
2. D D’Zurko, JL Rose, M Avioli, PJ Mudge, P Catton, ‘Validation and enhancement of long range guided wave
ultrasonic testing: A key technology for direct assessment of buried pipelines’. Final Report, DoT contract:
DTRS56-05-T-0002, 2007
3. P Catton, PJ Mudge, D D’Zurko, JL Rose, ‘An improved methodology for guided wave inspections of
pipelines’, Pipeline and Gas Journal, June 2008, pp 36-44.
4. R Sanderson and PJ Mudge, 'Flaw Characterisation Using Guided Waves', TWI Report 19239/3/13, 2013.
5. ‘Guided wave UT Target items for go-no go procedures’ (the ‘18 point’ guidelines), publ. PHMSA, November
2007.
Price and Duration
The overall estimated price for the work is £375,000 (excluding VAT), which requires £25,000 per company per
annum for 3 years (£75,000 total) from each of the 5 Sponsors. It is anticipated that the project will commence
with an agreed scope of work with a minimum of 3 Sponsors.
Further Information
For further information on how a Group Sponsored Project (GSP) runs please visit:
http://www.twi.co.uk/services/research-and-consultancy/group-sponsored-projects/
GSP Co-ordinator: Tracey Stocks
Email: gsp@twi.co.uk
Project Leader: Peter Mudge
Email: peter.mudge@twi.co.uk
Copyright © TWI Ltd 2013