Semi-Quantitative Risk Model for Managing the Integrity of Subsea Pipelines

Introduction

Pipelines, which transfer hydrocarbon products across thousands of miles, are an integral part of the oil and gas supply chain. This makes the integrity of the pipeline network a high priority; pipelines need to be inspected and tested to ensure their mechanical integrity. Many plants follow a time-based inspection approach without considering the associated risk of each pipeline. Nowadays, the general industry practice is that a risk-based integrity management approach, commonly referred to as risk-based inspection (RBI), should be applied.

The intention of using a risk-based approach is that the inspection activities are selected and scheduled based on their ability to explicitly detect, characterize, measure, and manage threats to the pipeline system and ensure that associated risks are managed to be within acceptable limits.

Methodology Overview

RBI methodology should consider the following:

• Identification of threats and failure modes
• Estimation of probabilities of failure (POF)
• Estimation of consequences of failure (COF)
• Estimation of risk level (COF × POF).

The POF should consider failure modes of operation, design, corrosion, and third-party impacts, while the COF covers probable environmental, human safety, and financial impacts. Failure is defined as failure modes of operation, design, corrosion, and third-party impacts. COF assessment covers the environmental impact and human safety.

The determination of the POF is carried out by assessing the remaining lifetime and by using the POF index procedure as illustrated in Figure 1. The minimum value of both is taken as POF.