An Integrated Approach For Underwater Survey And Damage Assessment Of Offshore Platforms
Authors: Kallaby Joseph , O&apos;Connor P.E. 
Published: October 2008

Ageing platforms form a substantial portion of the platform inventory in the Gulf of Mexico, and to a lesser degree, elsewhere. The need for assessment of these platforms is highlighted by the recent issue of Draft Section f 7of AH RP 2A-WSD. Although platform maintenance has been ongoing for decades, it still lacks uniformity consistency and an integrated approach for planned maintenance. This paper outlines such an approach, discusses the essential elements of a planned maintenance program, provides guidelines for survey planning and assessment of damage and presents damage threshold guidelines. The paper is based on extensive work carried out by Amoco in the North Sea, and later used as a basis for planned maintenance work in the Gulf of Mexico and elsewhere.

INTRODUCTION

The Gulf of Mexico (GOM) is the birthplace of the offshore platform in the early forties. It is currently populated with over 4000 fixed platforms of all configurations, in water depths up to 1350 feet. While platforms are maintained and repaired when needed, there is no industry guideline for uniform procedures for accumulating, documenting and evaluating quality survey data. With a sharp increase in the number of ageing platforms, maintenance has become essential. The authors suggest that an integrated approach be established leading to a uniform and cost effective maintenance program, which combines all tasks essential for platform assessment, including underwater surveys and data management.

API has recognized the need for uniform assessment guidelines, and has completed a Draft Section 17 "Assessment of Existing Platforms" of RP 2A-WSD currently out for industry comment. The draft is mainly based on GOM experience. This paper is one of six papers being presented at the OTC, each dealing with a specific aspect of the assessment process3,4,12,13,14.

WHAT IS AN INTEGRATED APPROACH?

The approach is an integrated maintenance program, referred to as Planned Maintenance. The program is based on over a decade of extensive maintenance work performed by Amoco in the North Sea. As a result, damage assessment and cost effective underwater surveys became routine, and platform repairs and strengthening minimal. A similar approach for the GOM region tailored by each operator for his platform inventory needs, would go a long way to establishing industry accepted guidelines, and provide a basis for similar guidelines elsewhere. The paper is not intended as a blueprint for such guidelines, but highlights the important tasks associated with an integrated approach, with emphasis placed on gathering and management of quality data, and subsequent damage assessment.

Platform Performance History:

Factors affecting platform performance history are outlined in Figure 1. These are "Quality" and "Exposure". As platforms age their resistance to loads generally decrease while their exposure to loads increase. The installation date is a key indicator of platform structural integrity, in that it reflects the state of the design and fabrication technology and code requirements at the time. Thus, the figure points out that older platforms benefit from more survey and assessment attention.