Subsea pipelines network represents a key component of oil and gas offshore operations, thus determining the integrity status for each pipeline to ensure a safe, reliable and cost-effective operation is crucial. It is always difficult to regularly check pipelines of tremendous length and large diameter, which are frequently laid in places that are not easily accessible. This paper presents a risk assessment model developed as part of a holistic study conducted to evaluate the condition of subsea pipelines. A systematic semi-quantitative risk-based model was developed to identify, analyze and evaluate risk associated with each subsea pipeline. The risk calculation combines the Probability of Failure (PoF) and the Consequence of Failure (CoF). The PoF calculations considered different factors, which believed to have direct impact on the likelihood of pipelines failure including: internal corrosion, hydrogen induced cracking (HIC) susceptibility and mechanical integrity. The CoF calculations factor safety, environment, economic and reputation impact. In overall, the study determined the risk level of each pipelines and provided measures and recommendations to lower the total risk.
The hydrocarbon exploration in the ocean and deep sea has started as early as early as 1850s, when the first drilling was carried out in California. Other early oil explorations activities were later recorded in Pakistan (1886), Peru (1869), India (1890) and Dutch East Indies (1893) (Hassan, 2008). In 1930s, the development of the Gulf of Mexico as an offshore area started with oil first being produced in 1938. The production from the North Sea has brought more technical challenges in to the offshore industry. The North Sea was first explored as a potential offshore area in the early 1960s (Patel, 1995). Since then the pace of oil exploration and production in shallow water has gradually increased to deep water with the exploration phase started in 1975 while production began twenty years later.
The development of an offshore industry is directly related to the development of subsea pipelines as well. As the industry expands towards deeper water envelopes, the pipelines are required to have better material designs, operation practices and maintenance strategies to withstand the challenging environments. These pipelines are exposed to elevated temperatures, high pressures, and corrosive fluids. Subsea pipelines Operators find it difficult to regularly check pipelines of tremendous length and with pipes of large diameter, which are frequently laid in inaccessible places. Besides corrosions, the pipelines are also exposed to hazards like extreme weather conditions, collision with vessels, trawl impact and pipeline span, as presented in Figure 1.