Underwater Inspection and Repair for Offshore Structures

 Underwater Inspection and Repair for Offshore Structures

Underwater Inspection and Repair for Offshore Structures

All structures deteriorate and experience damage with time, particularly due to fatigue cracking, corrosion and damage from extreme and accidental events. This requires inspections, monitoring and appropriate repair of these structures to be performed to avoid an unsafe condition. Significant research and development work have been undertaken related to typical damage types, inspection and monitoring methods, evaluation of damage, and the need and methods for repair. This book aims at giving the reader an overview of this research and development work in addition to providing current practice in these areas, both to inform the reader about the existence of this work and to avoid unnecessary repetition of research and development.

Since early 1980 the first author of this book, John V. Sharp, has been active in the majority of these research programmes through his role initially in managing the relevant UK Department of Energy research work and later as Head of Offshore Research for the UK HSE. Since early 2000 the second author, Gerhard Ersdal, has had
similar roles in managing several research programmes funded by the Norwegian Petroleum Safety Authority. Both authors have specific relevant expertise and have published a number of papers on inspection and repair of offshore structures and both are now actively involved in these areas at the universities of Cranfield and Stavanger, respectively, as Visiting (part time) Professors.

This book has mainly been written by using online web conferencing and in its later stages this has been forced upon us because of the Covid 19 lockdown in the UK, Norway and many other parts of the world. The opinions expressed in this book are those of the authors, and they should not be construed as reflecting the views of the organisations the authors represent. Further, the text in this book should not be viewed as recommended practice but rather as an overview of important issues that are involved in the management of inspection and repair.

Offshore structures for the production of oil and gas have a long history. The early offshore oil and gas exploration started in the 1940s in the Gulf of Mexico (GoM) andthe Caspian Sea 4 . This was followed by the development of the North Sea and Brazil in the 1960s and later activities in the Persian Gulf, Africa, Australia, Asia and other areas. More recently offshore structures for wind energy production have been developed, initially in Denmark in the early 1990s followed by significant growth in several European countries, particularly the UK.These offshore structures are continuously exposed to:
a sea water environment, which can cause corrosion and erosion; active and environmental loads, which may cause fatigue cracking and buckling;and incidents and accidents causing physical damage such as dents and bows.Damage of these kinds can cause loss of integrity of the structure and decrease the margin of safety. In addition, many oil and gas structures and the earliest of the wind structures are now ageing and many have been through a life extension process.

Nevertheless, there is a continuing requirement to demonstrate that these installations remain safe for the personnel that operate them. Unfortunately, there have been a number of accidents over the years with considerable loss of life resulting from structural failures related to inadequate inspection or failure to mitigate anomalies.

lack of in service inspection, which led to a catastrophic failure. Other accidents with serious loss of lives have occurred in which structural failure played a part. In the shipping industry the MV Erika and MV Prestige accidents are examples of structural failures in storms where anomalies in these vessels failed to be detected and mitigated. It is clear from these accidents that in service inspection and repair of structures are vital for the safety of structures. In addition, these are also normally required by regulators and class societies (i.e. ship classification societies, alsoknown as ship classification organisations).
There are numerous incidences of damage and deterioration that had they not been detected by inspection and subsequently repaired or remediated could have led to serious accidents and loss of life. As later shown in this book these types of damage and deterioration include severe corrosion, fatigue cracks, dents and bows from impact loads, and severed members that could have resulted in more widespread structural failure and ultimate collapse of the structure. While these instances are well known to the companies involved and the relevant regulators, they are not necessarily well reported in the public domain. However, they show the importance and value of undertaking inspection and repair in a timely way for the prevention of escalation and maintaining safety. In addition, many offshore structures are now in an ageing phase where inspection and repair are likely to be more important. The authors believe that this is an opportune time to review this previous work on inspection, evaluation, repair and mitigation of such structures.

There are few books on underwater inspection and repair and those that exist are now significantly out of date. However, a significant amount of previous work is available from research and technology developments on the topic providing an extensive expertise accumulated in inspection and repair of structures through many years of offshore operational experience. Unfortunately, many of these reports are presently unavailable in the public domain.

This book is intended to indicate the current practice in these fields for those involved in keeping offshore structures safe, including practicing engineers involved in structural integrity management and also for students in the field


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