Two years ago this month I wrote this blog article: "Should Engineers Always Perform Waterhammer Analysis of New Pipe Systems?". This was a popular blog. It was written from the fluid dynamic engineer's perspective.
Last month I was teaching an AFT Impulse training seminar and this same question came up during the class from an astute attendee. However, the question came more from a pipe stress engineer's perspective. And I realized that the answer to the question is not necessarily the same for a pipe stress engineer. Thus came the idea to write a Part 2 to the previous blog.
A fluid dynamic engineer's interest in waterhammer is typically to make sure the pipe system is designed and/or operated in such a way that the maximum allowable pressure is not exceeded. However, a pipe stress engineer's interest in waterhammer encompasses the fluid dynamics engineer's interest but also includes making sure the pipe supports are adequate to support the resulting loads from waterhammer. Adequacy in pipe supports includes proper placement, proper type and proper strength.
Among the features in AFT Impulse is the capability to predict imbalanced forces on pipes. I discussed this capability back in 2012 here: "May the Force Be With You: Evaluating Unbalanced Forces Caused by Waterhammer". This capability is used frequently by AFT Impulse users to generate loads for pipe stress analysis.
The astute engineer in my training seminar last month I mentioned earlier shared images to the class from a waterhammer event. In that event the pipe did not burst but was moved significantly from its supports and incurred significant damage to the insulation. And it is this aspect of waterhammer that adds a new wrinkle to the question "Should Engineers Always Perform Waterhammer Analysis of New Pipe Systems?"
Specifically, even when pumping benign fluids under otherwise acceptable pressure levels, the potential for imbalanced forces and their impact needs to be included among the reasons to perform a waterhammer analysis. A quick check of the surge pressure obtained from the Joukowsky Equation applied to the pipe area of interest would produce a force that in most cases is worst case. However, often that force calculation is too severe and a better force calculation is necessary. In such cases some kind of more in depth waterhammer analysis will be required. This is another reason for engineers to consider performing waterhammer analysis on new pipe systems.