Understanding Waterhammer in Pumping Systems and Surge Suppression Options
AFT Impulse™ Technical Paper
Authors: Trey Walters, Applied Flow Technology, USA, with Amy Marroquin and Frank Smith III, BLACOH Surge Control, Riverside California, USA
Presented at the 48th Turbomachinery & 35th International Pump Users Symposia Houston, Texas USA | September 9, 2019 – Copyright © 2019, by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station
Abstract
Waterhammer in pumping systems is an area of frequent concern to designers and operators. Waterhammer has the potential to cause catastrophic failures if not properly addressed. System designers have multiple options to mitigate waterhammer in the basic design. These include pipe system design, check valve selection and motor or pneumatically operated valve selection and actuation. In some cases, surge suppression is required. Suppression options include surge vessels, relief systems, vacuum breaker valves and air release valves.
This paper provides an overview of the waterhammer phenomenon, resources for engineers to assess waterhammer issues at the design stage and, for problematic systems already in operation, the issues involved with various surge suppression options.
CONCLUSION
Waterhammer is an important issue to consider in pumping system design. It impacts maximum pressures, pipe structural support design and safety of pure fluids inside the pipes. Various options to control waterhammer exist and should be considered when unacceptable pressures result during system operations.
Below is an excerpt. Use the links above to view the full paper.
Introduction
Waterhammer (also known as surge) occurs when fluid velocity is changed by actions such as valve position changes and planned or unplanned pump trips. Little guidance exists in codes and standards, and accidents are more frequent than we would like to admit. It is the purpose here to summarize existing knowledge and practice on waterhammer, discuss the abilities and limitations of commonly used calculation methods, provide warnings on what may happen when systems experience phenomena such as transient cavitation and liquid column separation, and give some high-level guidance on how to solve surge issues in pumping systems.
Waterhammer is fundamentally the same phenomenon across all industries which need to transfer fluids. However, depending on the nature of the fluid (benign, toxic, flammable, biologically active, etc.) and nature of the application (high pressure, proximity to people, remotely located such as in Space) different concerns and strategies are involved. It is essential that engineers take proper precautions in their design and operations to ensure safe operation of pumping systems.
APPLICABLE CODES AND STANDARDS FOR WATERHAMMER
Unfortunately, very little guidance exists from codes and standards on waterhammer. In practice, engineers are expected to use judgement and experience. Here are two excerpts from ASME piping code:
ASME B31.4: “Surge calculations shall be made, and adequate controls and protective equipment shall be provided, so that the level of pressure rise due to surges and other variations from normal operations shall not exceed the internal design pressure at any point in the piping system and equipment by more than 10%.”
ASME B31.3: “In no case shall the increased pressure exceed the test pressure used under para. 345 for the piping system.” And “Occasional variations above design conditions shall remain within one of the following limits for pressure design: Subject to the owner’s approval, it is permissible to exceed the pressure rating or the allowable stress for pressure design at the temperature of the increased condition by not more than 33% for no more than 10 hr at any one time and no more than 100 hr/yr or 20% for no more than 50 hr at any one time and no more than 500 hr/yr.”