Non-destructive Testing and Repair of Pipelines

Transmission pipeline systems have supreme significance for an effective functioning

of the petroleum industry, providing European market with energy

resources: crude oil, natural gas, liquid petroleum products, and liquefied natural or

petroleum gas. Taking into account the long life of such pipeline networks and the

present situation, with over 20% of the large-diameter pipelines having exhausted

their lifetime, an important task at the present moment becomes safeguarding the

reliability for these transmission systems. In such a context, pipeline maintenance

activities (comprising inspection and repair) are very important. Many studies have

proven that among the main reasons of steel pipeline failures are the volumetric

surface defects (VSDs, also named local metal loss defects), generated by corrosion

and/or erosion processes and by this way considerably decreasing the pipeline

strength and expected lifetime.

The present book is devoted to a provision of efficient and safe operations of

transmission pipelines by improvement of existing and development of new

methods for the detection (by means of non-destructive techniques, based on

low-frequency ultrasonic testing with directional waves) and repair (using advanced

composite materials systems) of VSDs, generated in the pipelines. These studies are

performed in order to bring the efficiency of damaged sections up to the level of the

undamaged pipeline. The combination of both research directions mentioned above

is, in our opinion, important since the increased technological opportunities of

long-range ultrasonic testing promote a more efficient application of composite

repair technologies, which are developed taking into account an assessment of the

stress–strain state in the VSD areas of in-service repaired pipelines.

The activities of transporting petroleum, natural gas and petroleum products are

services that must be provided continuously. As a consequence, the present-day

maintenance strategies require that the inspection and technological repair procedures

normally used should be applied without removing the pipelines from service.

In such conditions, the pipe repair systems, based on composite materials (that are

analysed in the present book), are more and more often used, because they have a

v

good economic efficiency. They considerably increase the remaining life of the

repaired pipelines and they do not require welding operations (implied by using

another repair methods, which require special precautions, when performed on

pipelines under pressure).

In order to ensure efficient and safe operation of existing transmission pipelines,

operating companies routinely inspect the pipes. The methods normally used to such

a purpose, like for instance “smart pigs”, are sufficiently expensive, require significant

reconstruction and have, in some cases, an insufficient sensitivity. As an alternative,

the application of long-range ultrasonic testing and phased array technologies,

studied in Chapter “Long-Range Ultrasonic and Phased Array Technologies”,

contributes to the increase of the functional capability of non-destructive testing,

namely range of test, defect detection, positioning and sizing capabilities.

Aiming at the development of recommendations for an application of the

long-range ultrasonic and phased array technologies for pipeline diagnostics, different

types of generated and received guided ultrasonic waves, their interaction

with discontinuities and directional properties of ultrasonic antenna array are

analysed. An accurate characterisation of damaged area detected in the transmission

pipeline by the long-range ultrasonic waves is carried out using the wavelet

transform and inverse techniques. The vibration-based damage detection (VBDD)

techniques, based on the changes in the dynamic characteristics of a structure

caused by the defect, are also analysed for steel pipeline systems. The localization

of impact damage in thin-walled composite structure using variance-based continuous

wavelet transform technique is investigated, and the defects identification

method in pipeline systems, based on a combination of finite element method and

artificial neural networks, is proposed.

The methods for the assessment of the pipeline areas, requiring maintenance

works, are performed. The remaining strength of a transmission pipeline on which

VSDs have been detected (using the results of non-destructive testing) are analysed

and compared in Chapter “T- and L-Types of Long-Range Guided Waves for

Defect Detection”, with the help of several case studies. The VSDs are characterised,

the criteria and procedures, defined by the norms presently used, are discussed,

focusing on the assessment of the remaining strength factor and residual life

of damaged pipelines. The procedures for the evaluation of the possible interaction

between several adjacent VSDs are also discussed and compared.

Different types of materials (polymeric fillers, fibre reinforced materials and

polymeric adhesives) are studied in Chapter “Directional Properties of Ultrasonic

Antenna Array” in their application to advanced composite repair systems. After

reviewing the properties of such materials, the methods of enhancing the strength of

adhesion interaction between the composite wrap/sleeve, used for repair and the

steel pipe, are analysed. The mechanical properties of composite materials are

characterised by both fracture methods (used to determine also dynamic characteristics)

and non-destructive techniques (impulse excitation and inverse technique,

vi Preface

based on low-frequency vibrations, laser-induced ultrasound, used to define elastic

properties), demonstrating the efficiency of the developed procedures and the

reliability of the obtained results.

The existing technologies using advanced polymeric composite materials systems

for the reinforcement of pipelines with VSDs are analysed and compared in

Chapter “Interaction of Low-Frequency Guided Waves with Discontinuities”, using

information from the manufacturers of such repair systems, the pipeline operating

companies and the experience of the authors. The technologies, based on composite

materials, used for pipelines coating to ensure their protection against corrosion, are

also present, together with repair methods for such coatings. The design methods,

applied for the definition of the characteristic dimensions (thickness and length)

of the composite wraps/sleeves, used in the repair systems, are also compared and a

new design procedure is proposed by the authors.

Many standards dealing with the composite repair systems are based on simplified

approaches and do not take into account the complex stress–strain state in

the damaged areas. Consequently, several analytical and numerical procedures,

presented in Chapter “Vibration-Based Damage Detection of Steel Pipeline

Systems”, are developed for the detailed assessment of the stress–strain state in

the repaired VSD areas. The recovery, by applying advanced composite repair

systems, of the carrying capacity of pipeline sections with local corrosion damage is

also analysed, using the finite elements method, considering also the case of pipes

with two interacting VSDs. Several analytical models, developed to model the

contact interaction between the steel pipe and the composite wrap, are also

described. An optimisation methodology, based on the planning of experiments and

response surface technique, is developed for the composite repair systems considerably

reducing the required computational expenses.

An experimental programme (comprising full-scale hydraulic tests of pipes

under inner pressure, up to bursting), developed and performed by the authors,

aiming at studying the reinforcement effects of a repair system using composite

materials for a damaged transmission pipeline, is described in Chapter

“Localization of Impact Damage in Thin-Walled Composite Structure Using

Variance-Based Continuous Wavelet Transform”. Validation of the developed

numerical models and estimation of the composite repair efficiency is made, based

on the results of such a programme.

The topics discussed and the solutions formulated in this book will be interesting

and useful for a wide audience, namely for students and researchers studying and

developing effective non-destructive techniques and advanced composite materials

repair systems for transmission pipelines, as well as for the providers or manufacturers

of the components of such techniques and repair systems and for the

engineers designing, planning and executing maintenance activities for different

pipelines belonging to the transmission systems of hydrocarbons or of other fluids.

The authors would like to express their gratitude to the European Commission

for the financial support of their research work under FRAMEWORK7 programme,

Preface vii

Marie Curie action, contract no. PIRSES-GA-2012-318874, project “Innovative

Non-destructive Testing and Advanced Composite Repair of Pipelines with

Volumetric Surface Defects (INNOPIPES)”.