Understand the Harmonic Analysis and Ensure the Pressure pulsation comply with API 674 (With PDF)

Harmonic analysis is the dynamic analysis used to predict the steady-state dynamic response of the piping system subjected to sinusoidally varying loads. All kinds of externally applied loads like nodal, elemental, gravity, and thermal loads can be included as load input. Accordingly, load cases are required to prepare and included in the solution. Load components in each load case use the same factor and phase angle. Different load cases may have different factors and phase angles, but the frequency for all loads is the same. The points that will be covered in this article are:

  • Introduction
  • Reviewing the Static Model
  • Creating the Harmonic input
  • The Harmonic Analysis
  • Result Review
  • Acoustic vibration and resonance is caused by Positive displacement pumps

Introduction to Harmonic Analysis

The harmonic analysis considers the effect of a harmonic load being applied to the system. The load is usually applied as a sinusoidal function (Fig. 1), e.g. pressure pulsation from reciprocating equipment. Being of a cyclic nature, harmonic loading relates to the fatigue allowable of the design code and should be considered. Care should be taken when undertaking a harmonic analysis for the accuracy of input data. Information relating to existing field problems can be derived from the measurement of pressure pulsation, deflection, forces, etc.

Reviewing the Caesar II Static Model for Harmonic Analysis

Introduction to Harmonic Analysis
Fig.1: Introduction to Harmonic Analysis

Creating harmonic Input for Analysis in Caesar II

Follow steps shown in Fig. 2

Steps for creating harmonic input
Fig. 2: Steps for creating harmonic input

The effect of damping on the response

Effect of Damping
Fig. 3: Effect of Damping

The Frequency-phase Dialog

The frequency phase dialog
Fig. 4: The frequency phase dialog

Harmonic Analysis Results Review


Nodal Movements in Harmonic Analysis
Fig. 5: Nodal Movements in Harmonic Analysis


Loads in Harmonic Analysis
Fig. 6: Loads in Harmonic Analysis


Stress Window of Harmonic Analysis in Caesar II
Fig.7: Stress Window of Harmonic Analysis in Caesar II
Occasional Stress
Fig. 8: Occasional Stress
Fatigue Approach
Fig. 9: Fatigue Approach
Updated Stress Results
Fig. 10: Updated Stress Results
Caesar II Steps for adding Fatigue data
Fig. 11: Caesar II Steps for adding Fatigue data
Updated Caesar II output result with Fatigue Data
Fig. 12: Updated Caesar II output result with Fatigue Data

Author: This presentation is prepared by Mr. Deepak Sethia who is working in ImageGrafix Software FZCO, the Hexagon CAS Global Network Partner in the Middle East and Egypt. He has extensive experience in using Caesar II software and troubleshooting.

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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.

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