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Macaw's Pipeline Defects

by Colin Argent, Kevin Prosser, David Norman, Peter Morganand Roger Weatherhead

Yellow Pencil Marketing; Publication Date: Aug 2003; ISBN0-9544295-0-8 (125.00)

The aim of this book is to illustrate the range of defects that may be encountered in high pressure steel pipelines and pipeline coatings. It gives advice on the probable cause and significance of the defects and comments on appropriate remedial actions. This book is not intended as a complete "Do It Yourself Manual" for the diagnosis and analysis of defects and use of this manual will not make the user an "Instant Expert". Many of the defects require analysis and diagnosis by a qualified expert using specialist analytical techniques.

The defects included in this book encompass all aspects of high pressure steel pipeline manufacture, construction and operation.

The section on manufacture includes defects in steel plate, seamless pipe and seam welds produced by electrical resistance welding (ERW) and submerged arc welding (SAW). Girth welds are dealt with in the section on construction along with poor construction practices such as lack of cover, electrical shorts, poor pipe support etc.

The section dealing with operational defects encompasses internal corrosion, external corrosion, erosion, fatigue, third party damage, denting and buckling.

Faults in the external corrosion control system are dealt with in separate sections. Coating defects are shown for the common types of mill applied pipe coating and field applied girth weld coatings. Common problems with cathodic protection schemes are also illustrated.

The final section of the book shows examples of the inter-action between fault conditions to create a new integrity risk to the pipeline; for example shielding of the cathodic protection by a disbonded coating to create the conditions for stress corrosion cracking.

Each section in this book has been compiled and edited by experienced engineers with many years practical experience in pipeline engineering, metallurgy, welding, coatings and corrosion. We believe this volume will provide a useful pictorial reference for engineers working in the pipeline industry. We would welcome constructive comment, suggestions or contributions that would enhance the practical value of future editions.

All photographs and information contained in this document are intended for guidance only. No comment or suggestion should be adopted as an authoritative action without seeking additional guidance from the relevant codes, procedures or specialist advisors. No responsibility can be taken for any problems which may arise as a result of the use of any information contained within this document.

Manufacturing Defects

The first section deals with defects that occur during steelmaking, rolling of the plate for pipe manufacture and the manufacturing process itself. In principle, all critical defects of this kind should be eliminated in the proof test carried out in the pipe mill.

Construction Defects

The second section considers defects that may be introduced into the pipeline during the construction process. Critical defects of this kind should be detected in the post construction hydrostatic pressure test.

Operational Defects

The third section of the book deals with defects that initiate and grow after the pipeline has been commissioned. These defects may initiate from a pre-existing fault within the pipe or they may initiate from an area of the pipe surface that is free of any manufacturing or construction faults.

Operational faults represent the largest problem for the pipeline operator who must assess which defects are likely to develop, the rate at which they will develop and the consequences for pipeline safety.

All of these issues are dealt with in the operational risk assessment for the pipeline and the findings of this risk assessment will decide the frequency and type of periodic proof tests or inspections designed to prevent operational failures.

Coating and CP Defects

The fourth section deals with defects in the external pipe coating and the cathodic protection system. These faults create the conditions in which external corrosion can develop.

Defect Interaction

The final section provides examples of how defects interact to generate new or modified risks to pipeline integrity.

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