Page 613 - Marine Structural Design

Part V

Risk Assessment

Chapter 34 Risk Centered Maintenance

34.1 Introduction

34.1.1 General
Offshore maintenance covers engineering tasks for various offshore facilities and equipment,
from the seabed to the topside. The tasks include routine maintenance, inspection and repair of
these facilities, and modifications I enhancements to the plant and the equipment.
The maintenance of offshore facilities presents many unique difficulties, which are not usually
encountered in inland applications. This is mainly due to factors such as:
Statutory requirements for safety are very restrictive
Improper maintenance often results in big losses in terms of safety, environment
protection, production, materials damage, and reputation in case of breakdown
Maintenance costs are relatively high due to high costs of manpower, offshore storage,
transportation between onshore and offshore, etc.
It is much more difficult to perform a maintenance task in the splash zone and subsea
Maintenance activities are often restricted by seasons (e.g. adverse weather conditions)
Logistics offshore can be the greatest problem to be resolved for an actual maintenance
task to be camed out
Therefore, operators for offshore installations usually establish good maintenance programs to
ensure that the production programs are met in terms of safety, reliability, availability, quality,
and quantity of supplies.
Scheduled (proactive) maintenance includes two major classifications:
Preventive Maintenance: Maintenance task frequencies are determined from a known
relationship between time (number of cycles, usage, age etc.) with reliability (survival
probability with respect to wear-out, corrosion, fatigue etc.).
Predictive Maintenance: Condition-based maintenance tasks are scheduled based on the
achievement of certain routinely measured conditions. The P-F interval is defined as the
distance from the point where we can find potential failure to the point where failure
actually occurs (Moubray, 2000). Condition-based maintenance tasks must be conducted at
intervals less than the P-F interval.
This chapter describes the application of risk analysis to maintenance of facilities on offshore
installations. It mainly consists of Preliminary Risk Analysis (PRA) and Reliability Centered