Risk Assessment & Management Based Criteria for Design and Requalification of Pipelines and Risers in the Bay of Campeche

Abstract

Risk Assessment and Management (RAM) based criteria for the design and requalification of pipelines and risers in the Bay of Campeche have been developed and implemented by PEMEX and IMP. The criteria address pipeline pressure integrity and corrosion, hydrodynamic stability, and capacity to withstand movements of the sea floor soils (the soft sea floor soils in the Bay of Campeche develop significant motions during hurricanes). The pipelines are assessed for three Safety and Serviceability Classifications. The SSC are based on risk acceptance criteria derived from considerations of economics, historic performance of pipelines, and current standards-of practice. Desirable and acceptable reliabilities of the pipelines for the three conditions cited are defined. Reliability formulations of pipeline 'demands' and 'capacities' are developed for loss of containment integrity due to corrosion, and hydrodynamic instability. Design for corrosion is linked to Inspection, Maintenance, and Repair (IMR) programs that will be implemented to manage corrosion. Uncertainties and biases associated with the analytical procedures are evaluated. Given the risk based characterizations, the reliability formulations, and the assessments of uncertainties and biases, design and requalification criteria are defined. Introduction At the present time, there are more than 500 km of pipelines located in the Bay of Campeche. These pipelines transport in excess of 2 million barrels of oil and 1.5 billion cubic feet of gas per day. The majority of the pipelines are located in water depths between 30 m and 50 m. Most of these pipelines were installed in the 1980's and 1990's, with some pipelines installed in the late 1970's. In October 1995, hurricane Roxanne formed in the western Caribbean Sea, crossed the Yucatan Peninsula, and entered the Bay of Campeche. Due to a southward moving front, the hurricane did not follow the normal northerly path of most hurricanes. It was forced back into the Bay of Campeche and the eastern coast of Mexico where it did considerable damage. Roxanne was the most severe hurricane to affect the Bay of Campeche during this century. It generated environmental conditions which approximated those of 100-year return period hurricanes.1 The majority of damage was confined to pipelines.2 Pipeline damage consisted of broken and leaking connections (above and under water), and damaged weight coatings. Given the results from the pipeline inspections and fitness for purpose studies, PEMEX and IMP initiated development of Risk Assessment and Management (RAM) based criteria for design and requalification of the pipelines in the Bay of Campeche. The RAM based criteria was to take advantage of the results from the oceanographic, pipeline design and inspections. and fitness for purpose studies, recent results from studI.es conducted by DNV3, AG4A, ISO5, BSI6, and API7 to develop advanced criteria for design of new pipelines and assessment of existing pipelines. Probability based reliability methods were used to evaluate the full scope (environmental and operating hazards), life-cycle (design, construction, operations, maintenance, decommissioning) risk characteristics associated with the Bay of Campeche pipelines (Risk Assessment).8–15 PEMEX and IMP utilized advanced risk management and decision analysis methods to define how the criteria should be defined to develop acceptable risks (Management).11,16,17

Factors of Safety for Design and Requalification of Pipelines and Risers in the Bay of Campeche, Mexico

“…ACi are the costs that are required to lower the probability of failure of the pipeline by a factor of 10. PVF is a present value function that brings to present day the future costs associated with the pipeline loss of quality or failure [3],…”

“…Based on current analyses of the causes of pipeline failures in the Bay of Campeche, in the case of pipelines, the probability of failure due to accidents, Pfa was taken equal to 0.25Pft; thus, the probability of failure due to operating conditions, Pfo is equal to 0.75Pft [3]. In the case of risers, which are located closer to human activity and at a higher risk of failures related to accidents, it was considered that the probability of failure due to accidents is 50% of the total probability of failure; thus, for risers, the probability of failure due to operating conditions is equal to 0.50Pft.…”

“…Information about pipeline failures in the Gulf of Mexico and in the North Sea indicates that Pfp=Pfs for pipeline and risers [3].…”

“…This format uses a nominal static loading to define the serviceability response characteristics and strength of the structure. Based on characterization of the demands and capacities as Lognormally distributed, the traditional factor of safety (FS) in working stress design [5] can be expressed as:…”

“…The bias (B) and uncertainties (v) for capacity and demand that are used in the obtaining of the factors of safety in the phase of design and reassessment for tension are proposed for Bea R. [5] and they are shown in table 1.…”