Important Considerations For Successful Fabrication Of Offshore Structures
Authors: Doody T.A. , Salama M.M. 
Published: October 2008

This paper addresses several key issues that are necessary to ensure the successful and sound fabrication of offshore structures. These issues are identified and based on the experience in the fabrication of major structures in both the North Sea and the Gulf of Mexico. The issues include project planning and organization; steel and fabrication specifications; quality assurance procedures; and causes, prevention, and resolution of fabrication problems.

INTRODUCTION

With the increasing Size and complexity of offshore projects, it becomes critical that certain aspects of fabrication be carefully considered and reviewed. The continuous expansion of offshore activities to deep water imposes stringent requirements on the cost, schedule, and quality of offshore structures. Neither the reliance on minimum code requirements nor over specification is appropriate. A rational review of performance requirements is necessary to establish realistic and meaningful specifications. The proper identification of the performance requirements during design and the efficient planning and implementation of quality assurance and control during fabrication are essential. These steps are the key to achieve the competing goals of enhancing the reliability and safety of the structure while also achieving a reduction in final cost. This paper draws from past experience in the fabrication of major offshore structures and recent advances in the area of structural steel and welding to identify the steps necessary to achieve successful fabrication. This paper addresses these topics:–Project organization–Fabricator experience–Specification requirements–Evaluation of new steels–Weldability–Fabrication quality control–Inspection–Use of Engineering Critical Assessment (ECA)

PROJECT ORGANIZATION

An important ingredient to ensure the success of any project is the utilization of proper project organization. For smaller, conventional offshore projects, a majority of the work is usually done by groups assigned product responsibility. This means that both engineering and fabrication are under the auspices of a single group. As the complexity of recent projects has increased, project organization has tended toward functional responsibility (Fig. 1), based on the need for more involved engineering tasks. This can lead to inter-group conflicts when problems arise during fabrication. In addition, the basis of detailed engineering requirements becomes removed from the fabrication site, causing delays and misunderstandings when difficulties require investigation and resolution. These difficulties with functionally-oriented organizations can be overcome with several developments consciously taken during the project organization. These include:The involvement of the fabrication group in the detailed review of design, purchase, and fabrication specificationsAn organized and timely procedure for investigating site queries for engineering evaluation or specification deviation.Shifting of key members of the design team to the fabrication group once construction has started. This allows for the rational and timely evaluation of fabrication difficulties as they arise.

Without this, even commonplace problems become difficult to resolve. With the large number of non-conformances to specification requirements that remain uncorrected on most major projects after installation, the question always arises as to the suitability of the original requirements (this also highlights the need for rational, performance-based specifications).