Evaluation of Below Ground Emergency Shutdown Valves in Sour Gas Pipelines

Abstract

The purpose of emergency shut-down valves (ESDVs) is to provide the capability of dividing sour gas pipelines into segments, which can be individually isolated during upsets or ruptures by closure of the ESDVs. CIMARRON Engineering Ltd. (CIMARRON) performed a study in 2003 to evaluate installing ESDVs below ground for sour gas pipelines. The direct burial advantages of easier pigging, reduction in pipeline stresses, smaller surface footprint, less visibility, lower installation and maintenance costs, less chance of vandalism, and less chance of unauthorized operation are all desirable. This direct burial option, using weld neck valves, is contrary to the conventional above ground installation with flanged valves, which dominates the practice in Western Canada. CIMARRON has used the criteria of feasibility, benefits, and limitations in evaluating the option of direct burial. To these three (3) criteria have been added measures to mitigate any identify limitations or constraints. In addition, piggability for cleaning and in-line inspection is considered to be a required feature for all sour gas pipelines. CIMARRON has reviewed and gathered extensive field data and background case studies for the preparation of this paper. In addition to the industry standard of above ground ESDVs, they are also occasionally installed in vaults. However, entry into any vault constitutes a “confined space entry” with its associated implications on safety. CIMARRON contends that if certain capabilities are provided for functional access from the surface to a buried ESDV, then compliance with all requirements of the governing legislation is possible without being able to physically see or access the buried valve. Enhancements to the responsiveness of ESDVs to pipeline upsets and failures are important. Using SCADA at both wellsites and ESDV sites can provide a significant advantage in limiting any potential sour gas releases. The simplifications associated with buried ESDVs can constitute a significant advantage. Taking all these aspects into consideration, there are substantial benefits to burying ESDVs when compared to both the above ground and vaulted options.