Identifying Cause of Rupture Disk Breaks at Alberta Capital Region Wastewater Commission Parkland Pump Station

This paper provides a case study to identify the cause of rupture disk breaks at the Parkland pump station and demonstrate the need to understand the limitations of hydraulic transient model software and importance of understanding the design and limitations of certain surge mitigation devices.The Alberta Capital Region Wastewater Commission (ACRWC) commissioned a study to complete a hydraulic transient analysis of the Parkland pump station and force main to evaluate the hydraulic conditions in the force main, determine the reason for the frequent rupture disk failures, and provide recommendations to improve system performance and minimize or eliminate future rupture disk breaks.The hydraulic transient analysis required a comprehensive data collection effort, construction and calibration of a hydraulic transient model, reviewing the failure history of the rupture disk and understanding operational conditions at the time of the failure, completing multiple scenarios to evaluate the effectiveness of each surge mitigation device, performing model runs using steady and unsteady transient friction methods due to limitations of the Method of Characteristics discrete vapor cavity model, and reviewing the design limitations of surge mitigation equipment.Study results indicate the maximum pressures experienced in the force main do not exceed the design working pressure of the pipeline. Although column separation and surge pressures are likely contributing to the failure of the rupture disk, model results do not indicate the disk is rupturing due to pressures within the force main exceeding the disk burst pressure rating. Per discussion with the rupture disk manufacturer, the disk may be failing due to fatigue as it is desirable for pressures to remain below 70% of the burst pressure rating of the disk for the type of disk used. Replacing the existing rupture disk with a reverse bucking rupture disk, which can accommodate pressure fluctuations up to 90% of the burst pressure rating without fatigue, could minimize or eliminate future rupture disk breaks.