Offshore asset maintenance and inspection programs have become increasingly widespread with the desire for improved safety, asset integrity, life extension, well control systems, and blowout prevention practices.

An example of this is a new inspection program being implemented on the UK Continental Shelf (UKCS) that is aimed at ensuring aging infrastructure does not have an adverse effect on safety.

Asset integrity on UKCS
Driven by the UK Health and Safety Executive (UK-HSE), the inspection program is part of a series of initiatives to regulate asset integrity. Known as Key Program 4 (KP4), it is the next stage in the Executive’s Aging and Life Extension Inspection Program and means operator assets will be subject to scrutiny by safety inspectors to ensure standards are maintained. The program will run until September 2013 and has the potential to impact the way operators manage the structural integrity of their assets globally.

This image shows an example of a collapse mode and stress state on a jacket leg when topside load increases. (Images courtesy of PSN)

There are more than 6,700 platforms in operation around the world. On average, 30% have been in operation for more than 20 years. In the North Sea alone, more than 50% fall into that category. Many of these are operating beyond their original design life, but as more oil and gas discoveries are made, operators are required to extend the life of their offshore assets without compromising asset integrity, reliability, productivity, and more importantly, safety.

Individual inspections of mature assets and life extension programs identify shortcomings and impose remedial actions. The belief is that KP4 will stimulate a common industry approach to managing aging installations that will ensure safe offshore operations for the long term. If this approach is adopted globally, much of the North Sea experience gained by companies in the UKCS can be transferred to operator assets in the Gulf of Mexico and beyond.

The spotlight that KP4 has focused on operators to take responsibility for managing the risks associated with asset integrity and life extension programs already has increased the profile and importance of structural integrity management. Operators are keen to increase the value of their assets, and a robust structural integritymanagement (SIM) system is seen as a function of critical importance to ensuring a safe working environment offshore.

SIM for life extension
A life extension project can increase the value and viability of an asset.

Demonstrating the structural integrity of aging assets is of paramount importance when considering life extension. There are regulations, assessment requirements, and guidelines published by various authorities for life extension. In Norway, an application for life extension is a formal requirement, and in the UK, a safety case must be reviewed when installation design life has been exceeded.

Corrosion is a common integrity issue because of harsh operating environments.

The effects of the Deepwater Horizon tragedy in the Gulf of Mexico has led to an announcement by the Bureau of Ocean Energy Management, Regulation and Enforcement that all operations and drilling facilities on the Outer Continental Shelf will be required to develop and maintain a safety and environmental management system (SEMS).

The SEMS Final Rule is designed to improve workplace safety offshore. The rule will hold operators accountable for overall facility safety, including ensuring that all contractors and subcontractors have safety policies and procedures in place that support the implementation of the operator’s SEMS program and align with the principles of managing safety set forth in API RP 75, the recommended practice for offshore oil, gas, and sulfur facilities and associated equipment.

This has a consequential affect on how operators manage asset integrity and impacts the process for considering asset life extension. The challenges commonly posed by life extension include:

-Corrosion – due to harsh environments;

-Overload – wave action, additional topsides, and environmental loads;

-Operational changes – platform modifications;

-Incidents – ship collision, explosion; and

-Fatigue – the deterioration of structural design.

Applying a structural integrity management system (SIMS) can help operators overcome these challenges.A SIMS provides structural integrity assurance for offshore assets covering topsides, jackets, appurtenances, and foundations. The primary activities normally undertaken to create a SIMS include producing key SIMS documentation and annual integrity summary reports, managing the platform inspection philosophy (topsides and subsea), reviewing inspection results, maintaining an anomaly database and engineering of anomaly repairs, emergency response services, and providing structural analysis models and a weight control database.

All of these components are required to extend the life of an asset or demonstrate enhanced structural capacity beyond the original design values.

A demonstration of enhanced structural integrity can involve sophisticated structural analysis techniques such as:

-In-place assessments;

-Progressive collapse and pushover analysis;

-Boat impact and redundancy analysis;

-Liner and non-liner finite element analysis;

-Structural dynamic assessment and post-buckling response;

-Blast assessments; and

-Fatigue and fracture mechanics.

SIMS principles
Asset integrity means an asset can perform its required function effectively while ensuring HSE.

All encompassing, structural integrity management systems now can provide complete engineering, integrity, and regulatory solutions that, when coupled with life extension developments, add real economic value to an asset.

Three areas are integral to effective structural integrity management: inspection, change management, and advanced analysis/ integrity assessment.

UK-HSE states that aging is not about how old the equipment is; it is about what is known about its condition and how that is changing over time. The optimal solution to managing structural integrity and reducing the risk of potential failures is to develop and integrate inspection strategies and work scopes from the original design phase of a development.

An integrated SIMS covers the development of such inspection strategies, work scopes, inspection results reviews, and the maintenance of inspection record databases. SIMS also makes it easier to identify and manage defect assessments and develop repair solutions, both for topsides and subsea.

Change management is required when modifications are made to an installation. Platform developments normally involve changes in the physical and operational parameters of a platform, and new developments often require operational changes as well as updated procedures. Modifications should be designed with an understanding of the brownfield environment.

The capacity of the existing structure to support modifications is key to this process. A SIMS specifies a weight control procedure that is implemented as part of good change management for any offshore structure or vessel.

A structural analysis computer model also must be developed for every installation to quantify the effect of any change on the structure. The main purpose of advanced analysis or structural integrity assessment is to ensure the structural critical elements are acceptable and that performance standards are being fulfilled. It also provides valuable input for the decision-making process surrounding platform life extension.

In a number of instances, PSN has adopted advanced analysis techniques to demonstrate enhanced structural capacity or to minimize the need for structural strengthening. Often this type of analysis is critical to the viability of the entire project.

Note: This work is based on an SPE paper delivered at ADIPEC 2010.