# Difference between Primary loads and Secondary loads in a Piping System

Piping Stress Analysis is the scientific or engineering study of all the stresses generated in a piping system. Now from where this stress comes? From the mathematical definition of stress, we all know that Stress is the Reaction Force per unit area. So, this clarifies that piping stresses are generated because of some kind of loads or forces in the piping system. The forces the piping system faces are categorized into two distinct groups.

1. Primary loads and

In this article, we will study the differences between these two types of load categories.

## What is a Primary Load in a Piping System?

Normally Force driven loads are called Primary loads. These loads are generated due to gravitational forces, internal or external fluid pressure, spring forces, relief valve discharge, pressure waves during water hammer or surge effects, etc. Hence, Primary loads originated due to some kind of force acting on the piping system. A large value of Primary loads creates plastic deformation leading to catastrophic failure. In a catastrophic failure, each individual crystal is subjected to stresses that the body can not withstand and causes rupture.

## What is a Secondary Load in a Piping System?

Secondary loads are usually displacement-driven loads. These loads are generated due to some kind of displacements imposed in the piping system, for example, thermal expansion, settlement, anchor movement, vibration, etc. Most of the time (not always, for example, tank settlement) these are cyclic in nature.  Such kind of loads normally results in fatigue failure. In fatigue failure, the grains collectively fail because of incremental damage done by each cycle.

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The following table lists the major differences between primary and secondary loads.

Few more useful resources for you..

Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

## 4 thoughts on “Difference between Primary loads and Secondary loads in a Piping System”

1. Junhyo Lee says:

Simple but fantastic explanation about self-limiting nature!!

2. Fahid Masood says:

Very Informative and summarised in a good way!

3. manish says:

Perfectly explain as it should be. Thanks a lot

4. Pai says:

Hello Sir,

I have a basic question.
does primary load induce secondary stress..?