Cost of Ownership: Part 2

Improving Cost of Ownership With Vibration Risk Reduction: Part 2 of 2  

Field Vibration Acceptance Testing (VAT), Vibration Analysis, and Modal Testing (Part 2 of 2) 

The Part 1 case history provides an overview about lowering the risk of vibration problems in new or modified plant designs. It also provides more detail about the specification writing and analysis portion of the risk reduction effort. This Part 2 case history discusses the post-installation vibration verification testing (lower right in Figure 1).

Summary 

Field Vibration Acceptance Testing (VAT) or verification testing plays a critical role in reducing vibration risk, improving rotating equipment reliability, and lowering total cost of ownership (TCO) for pump, blower, and centrifuge systems. Beyond confirming compliance with industry vibration standards such as ANSI/HI 9.6.4, ISO 10816, and API, advanced vibration testing techniques—including vibration test data analysis, experimental modal analysis (impact) testing, and motion magnification video—help identify and mitigate resonance,  misalignment, imbalance, and structural issues before plant startup. In many cases, impact testing producing Frequency Response Function (FRF) plots are used to ensure compliance with specified natural frequency separation margin criteria.

When performed by an independent testing firm, these methods provide measurable long-term benefits such as reduced maintenance costs, extended equipment life, improved uptime, and enhanced predictive maintenance capabilities.

Figure 1. Answers the question “At what point in a project timeline should vibration expertise be used to help reduce risk for a successful new or modified plant design?” Red Box at lower right is covered by this Part 2 Case History with the remainder being covered in Part 1.

Why VATs and Verification Testing Matters

What Is the Primary Purpose of a VAT? 

The most obvious objective of a field VAT is to confirm that rotating equipment—such as pumps, blowers, or centrifuges—meets the overall vibration acceptance criteria specified in the project documents.

Commonly referenced standards include:

• ANSI/Hydraulic Institute Standard 9.6.4 (pumps, Figure 2)
• ISO 10816 (rotating machinery)
• API vibration standards
• Owner- or AE-firm-specific vibration limits

However, compliance alone does not guarantee long-term reliability or low operating costs. 

Understanding Overall Vibration Measurements 

How Is Overall Vibration Measured During Testing? 

Overall vibration levels are typically recorded at specified measurement locations and in three orthogonal directions (horizontal, vertical, axial) while the equipment operates within its acceptable operating range.

Figure 2 (one example deliverable):

• Displays overall vibration levels at one measurement location
• Includes multiple operating speeds for variable-speed equipment
• Confirms vibration acceptability across the operating envelope

Figure 2. Example overall vibration measurement compared to the HI acceptance criteria for a specific type of pump at a single location and running speed (measured in three directions). The number of specified measurement locations is dependent on the pump type.

Why FFT Vibration Analysis Should Be Required 

What Is FFT Vibration Analysis and Why Is It Important? 

Specifications should require delivery and analysis of Fast Fourier Transform (FFT) vibration plots, also known as vibration signatures (or filtered plots) even if the referenced standard such as HI 9.6.4 does not require this activity. FFT plots display vibration amplitude versus frequency, enabling early detection of mechanical and structural issues.

Common Issues Identified Using FFT Analysis

• Shaft imbalance
• Coupling or piping misalignment
• Mechanical looseness
• Internal rubbing
• Vane pass frequency excitation
• Can initially identify possible resonance

Figure 3 (example FFT deliverable):

• Measures vibration amplitude at important excitation frequencies (1/2 running, running speed, multiples of running such vane pass frequency, and unusual non-synchronous frequencies)

• Identifies the separation margin between excitation frequencies and natural frequencies

• Enables corrective action, if needed.

Figure 3. An example FFT comparing vibration magnitude versus frequency indicating a pump with good vibration characteristics and a lower probability of encountering a resonance issue. The experienced pump engineer identified the maximum running speed (1x) and vane pass frequency (2x for a 2 bladed pump). They have also labeled the approximate frequency of the first and second structural natural frequencies.

Key Insight:
FFT analysis adds minimal cost and schedule impact while delivering significant risk reduction and long-term value. 

Experimental Modal Analysis: Predicting the Future

How Does Impact Testing Lower Cost of Ownership? 

If reducing total cost of ownership is a project objective, experimental modal analysis (impact testing) should be specified.

An impact test allows engineers to:

• Identify system natural frequencies

• Evaluate structural and acoustic vibration modes

• Predict future resonance risks as equipment ages

Frequency Response Function (FRF) Plots Explained

What Is an FRF Plot and Why Does It Matter? 

Figure 4 shows a Frequency Response Function (FRF) plot, a key deliverable from impact testing.

FRF plots are used to:

• Confirm no structural or acoustic resonance exists in the rotating equipment or connected piping

• Verify frequency separation margins between excitation sources (e.g., running speed) and natural frequencies—typically 15% or greater

• Assess long-term resonance risk due to stiffness changes, wear, or operating condition changes over time (i.e., aging plant issues)

Figure 4. Example Frequency Response Function (FRF) plots based on specialized impact test results. FRFs are used to help an experienced pump engineer differentiate between benign structural natural frequencies versus natural frequencies that could lead to a resonant (high vibration) condition. This is particularly important for variable speed equipment and pumps with a low impeller vane count.  

Motion Magnification Video: An Emerging Best Practice 

What Is Motion Magnification and When Should It Be Used?

Motion magnification video is an emerging vibration verification technology originally developed for troubleshooting but now increasingly used for validation testing.

Figure 5 (motion magnification example):

• Uses high-speed cameras and specialized software

• Exaggerates and slows system motion

• Reveals dynamic behavior invisible to the naked eye

Figure 5. Static image of a Motion Magnified Video (MMV) is a troubleshooting test method that is emerging measurement tool for vibration verification testing. It is also currently used to test a pump system prior to it being modified. This is motion magnified video of a vertical turbine pump with a soft foot issue due to a loose anchor bolt (see video below).

Capabilities include:

• Detecting displacements as low as 0.1 mil peak-to-peak

• Visualizing structural, piping, and baseplate vibration

• Excellent for measuring vibration of piping and other elevated machinery and structures from a safe stand-off distance (50 feet plus)

Vibration Data as a Predictive Maintenance Baseline 

How Can Verification Testing Support Predictive Maintenance? 

Vibration data collected during VAT serves as a baseline “birth certificate” for the equipment. When combined with a predictive maintenance program, this baseline enables:

• Accurate vibration trending

• Early fault detection

• Reduced unplanned outages

• Lower maintenance and repair costs

• Safer machinery operation

Long-Term Benefits of Independent Vibration Testing 

Implementing vibration analysis and VAT through an independent testing company significantly reduces risk for:

• Plant owners

• EPC contractors

• Engineers

• Equipment manufacture

Over the life of the facility, these practices deliver:

• Improved equipment reliability

• Reduced vibration-related failures

• Lower operating and maintenance costs

• Measurable reductions in total cost of ownership

Frequently Asked Questions  

What vibration standards are commonly used for pump testing? 

ANSI/HI 9.6.4 is most commonly specified for pumps for many applications such as water, wastewater, and flood control, while ISO 10816 and API standards are often used for other rotating equipment including oil and gas, power generation, and industry.

Is FFT vibration analysis required by industry standards? 

FFT analysis is not always required, but it is highly recommended because it identifies root causes of vibration that overall vibration levels alone cannot reveal.

What separation margin is typically required between excitation and natural frequencies? 

Most specifications require a minimum 15% separation margin to avoid resonance if modern analysis methods are being used by an experienced engineer.

How does vibration testing reduce lifecycle costs? 

By identifying vibration issues early, vibration testing prevents premature failures, reduces maintenance costs, and extends equipment life.

Is motion magnification replacing traditional vibration testing? 

No. Motion magnification complements traditional vibration testing by providing visual confirmation of dynamic behavior.