Pipe Stress Analysis from Water Hammer Loads

It is well-known that water hammer is caused in a piping system by sudden closure or opening of the valves or due to pump trips. During those events, the pressure increases to a huge extent and that causes an unbalanced load in the piping system which is known as Water hammer loads. All these loads created due to water hammer acts in the changes in directions and can be of sufficient magnitude to cause the piping system failure. So, during the design phase, water hammer analysis must be performed to calculate the water hammer loads and design piping and support systems to avoid failures. In this article, we will discuss the pipe stress analysis methodology for water hammer loads.

In piping systems, sudden changes in flow cause pressure unbalanced forces between elbows, valves, tees, reducers, and other inline components. These forces damage the piping system when it is not properly designed to accommodate them.

The main advantage of using PASS/START-PROF + PASS/HYDRO SYSTEM is that the 3D piping model can be easily converted between these software packages both ways.

3D piping model from PASS/START-PROF can be converted into the 3D piping model in PASS/HYDRO SYSTEM, then generate 3D water hammer loads for all nodes at certain moments of time (not only just in one node!) and pass it directly into stress analysis software PASS/START-PROF automatically (not manually!).

PASS Suite START-PROF + HYDRO SYSTEM allows us to model it very easily, just in several clicks, and help to find a way to reduce water hammer damage to the piping system. Let’s study how to perform stress analysis of the piping system from water hammer loads.

The simple piping system created in PASS/START-PROF software is shown on below screenshot:

Simple Stress System for Water hammer load explanation
Simple Stress System for Water hammer load explanation

After saving the PASS/START-PROF file, we can open it using PASS/HYDRO SYSTEM software.

Importing the file in HYDROSYSTEM
Importing the file in HYDROSYSTEM

Set pressure 0.15 MPa at node 1, and 0.16 MPa at node 11

Inputting for Water hammer Analysis
Inputting for Water hammer Analysis

Choose water steam library

Choosing Object properties for Water Hammer Analysis
Choosing Object properties for Water Hammer Analysis

Define the period of surge analysis 2.5 sec, data output stem 0.01 sec, and dynamic load factor DLF=2.0.

Entering Dynamic parameters for Water hammer loads
Entering Dynamic parameters for Water hammer loads

Select Valve in node 12 and in the “Waterhammer” tab set that valve is immediately closed.

Setting the valve for Water Hammer Analysis
Setting the valve for Water Hammer Analysis

Run Isothermal Flow analysis

Calculating isothermal Flow
Calculating isothermal Flow

Run water hammer analysis

Running the Water Hammer Analysis

Running the Water Hammer Analysis

After that export unbalanced pressure forces into (.ctpf) file. Also HYSROSYSTEM allows to export data into (.frc) file that can be opened by CAESAR II.

Exporting Unbalanced pressure forces into FRC file
Exporting Unbalanced pressure forces into FRC file

(.ctpf) file contains forces multiplied by DLF factor for all nodes in piping models at several most dangerous moments of time. The most dangerous moments of time is found automatically by HYROSYSTEM software.

Force vs Time Plot for water hammer loads
Force vs Time Plot for water hammer loads

This is the (.ctpf) file structure

Structure of CPTF file
Structure of CPTF file

This means, that PASS/HYDROSYSTEM generates unbalanced pressure loads for all nodes in the piping system at a certain moment of time.

Water Hammers loads with respect to Time
Water Hammers loads with respect to Time

Now open PASS/START-PROF, open Operation Mode Editor and import waterhammer forces into first operating mode.

Importing water Hammer loads
Importing water Hammer loads

Eight additional force-based load cases are imported from the file

Creating additional load cases for water hammer analysis
Creating additional load cases for water hammer analysis

You can check the force values at any node properties

Water hammer loads at nodes
Water hammer loads at nodes

Now run piping stress analysis and see results

Deformed Shape at any moment of time

Deformed shapes due to water hammer loads
Deformed shapes due to water hammer loads

Stress table at any moment or time

Stress Table during water hammer analysis
Stress Table during water hammer analysis
Detailed stress value during water hammer analysis
Detailed stress value during water hammer analysis

And maximum stresses from all load cases (static and all moments of time during waterhammer)

Maximum stresses
Maximum stresses

The same table can be checked for displacements, support loads, flange leakage, expansion joint deformations, etc.

Output results
Output results

Watch the following video with detailed analysis process described above:

Video Tutorial for Pipe Stress Analysis from water hammer loads

Some more ready references for you…

Introduction to Pressure Surge Analysis
Water Hammer Basics in Pumps
Understanding Centrifugal Compressor Surge and Control
Stress Analysis using Start-Prof

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Alex Matveev

Alex Matveev is one of the authors of pipe stress analysis codes GOST 32388-2013 Process Piping, and GOST 55596-2013 District Heating Networks. He is also one of the developers of PASS/Start-Prof software, which is developed since 1965 and used in 95% of process, power, district heating, gas and oil transportation design companies in Russia and CIS countries; it is industry standard in that region. He is the head of the PASS/START-PROF pipe stress analysis software development team. Also, He offers technical support and training for users of their software that number already 3000+, developing since 1965, industry standard in several countries for 50+ years, translated into English in 2017, come out from their domestic market, and started sales for the international market since 2018.

One thought on “Pipe Stress Analysis from Water Hammer Loads

  1. what is the advantage of used spring loaded zero velocity valve in place of conventonal NRV in water supply pipe line pl discuss

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