Reliability and Integrity Analysis of an Air-Cooled Heat Exchanger: A Case Study

Air-cooled heat exchangers (AC-HEs) are used extensively throughout the oil and gas industry, from upstream production to refineries and petrochemical plants, under high pressure and high temperature conditions, as well as corrosive fluids and environments. Some defects and discontinuities can be introduced during the heat exchanger manufacturing process and are not necessarily found as part of QA/QC inspections. Other damage mechanisms (e.g. erosion-corrosion, sulfide stress corrosion cracking, thermal fatigue, and pitting corrosion due to CO2 or because of chloride content in the process stream) can occur while heat exchangers are in service. Equipment complexity, which can make inspection challenging, and the safety, environmental and business consequences in case of equipment failure (loss of containment), justify that a good asset integrity management program be developed and applied. An asset integrity management program seeks to ensure that all equipment, especially pressure equipment, where loss of containment/failure is unacceptable, is designed, constructed, inspected, and maintained to the appropriate standards and best practices. Simultaneously, maintenance efforts should be optimized to be cost-effective, thus, guaranteeing a sustainable and safe operation.

This article covers a reliability and integrity process analysis of an AC-HE in hydrocarbon service. This process, as part of an Asset Integrity Management Program (AIMP), includes a Risk Based Inspection Strategy (RBIS), Acoustic Pulse Reflectometry (APR) inspection and degradation analysis as part of the remaining life assessment (RLA). The work process helps engineers, maintenance managers and plant managers make informed decisions, even in an uncertain environment.

Background

A recent HSE Survey, “Ageing Plant Study Phase 1,” sheds light on the various issues that age-related deterioration brings to plants:

Recent research shows that 50% of European major hazard “Loss of Containment” events arising from technical plant failures were primarily due to ageing plant mechanisms such as erosion, corrosion and fatigue. This data analysis for HSE has shown that across Europe, between 1980 and 2006, there have been 96 major accident potential loss of containment incidents reported in the EU Major Accident Database (MARS) which are estimated to be primarily caused due to ageing plant mechanisms. This represents 30% of all reported ‘major accident’ loss of containment events in the MARS database, and 50% of the technical integrity and control and instrumentation related events. These ‘ageing’ events equate to an overall loss of 11 lives, 183 injuries and over 170Million € of economic loss. This demonstrates the significant extent and impact of ageing plant related failures on safety and business performance.1