Vibration, dynamics and noise

formerly BETA Machinery Analysis and SVT Engineering Consultants

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GMRC Gas Machinery Conference 2020

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Week 1
Solving small-bore problems for compressors and associated piping

Tuesday, October 6
9:00 AM–10:30 AM

Small-bore connections (SBC) on compressor packages and piping are prone to failure, and available guidelines are not widely applied.

On new designs, standard practices can prevent failures but may be difficult to balance with varying client requirements. In these instances, application of guidelines and more advanced analysis can determine safe design solutions.

On existing systems, the same techniques and processes can be applied to focus analysis and mitigation efforts to reduce failure risks.

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Foundation design practices for rotating machinery

Wednesday, October 7
9:00 AM – NOON

Background

A well-designed foundation is essential for reciprocating and rotating machinery installations to operate in a safe and reliable manner for many years. Design of foundations is often focused on static design principles that are well known to many engineers.

There is a general lack of appreciation and understanding of dynamic design principles for machinery foundations. Reciprocating compressor foundations are a particular challenge due to the high amplitude and complex dynamic loads resulting from normal operation.

Based on Wood’s extensive experience in this field, a good foundation design requires consideration of static and dynamic loading, soil dynamics, machinery generated dynamic loads, and basic static and dynamic design principles.

Objectives

The goal of this short course is to provide insight into static and dynamic design considerations and best practices for different types of foundations supporting rotating machinery packages.

Course outline

1. Overview of vibration

  • Review of key terminology used in the industry
  • Overview of vibration causes of vibrations
  • The vibration equation
  • Introduction to reciprocating and rotating machinery
  • Dynamic loads generated by centrifugal and reciprocating machines
  • How to consider dynamic loads to create a reliable foundation design

2. Types of foundations

  • Overview of foundations types commonly used to support centrifugal and recipro- cating machines
  • Concrete block and elevated (table top) foundation
  • Pile foundations including driven and screw piles
  • Gravel pad foundations

3. Static and dynamic design considerations

  • Static and dynamic design principles for different types of foundation
  • Rule of thumb for foundation sizing
  • Basic static checks
  • Soil dynamic properties
  • Design goals such as resonance avoidance
  • Design principles for each foundation type

Case studies

Multiple case studies will be presented to demonstrate the discussed design principles.


GMRC research update – fiberoptic strain pulsation measurements

Wednesday, October 7
1:15 PM – 2:00 PM

Dynamic pressure measurement in pipelines and pressure vessels is a common practice for vibration and pulsation troubleshooting. Data processing of dynamic pressure signals can reveal the root cause of vibration problems such as high pulsation-induced shaking forces, flow-induced vibration (FIV), flow-induced turbulence (FIT) or acoustic-induced vibrations (AIV).

Piezoelectric pressure sensors are typically used for dynamic pressure measurements. These sensors are invasive devices and have transducers that come into contact with the flowing fluid.

They are also called ‘wetted’ transducers. These invasive sensors can only be installed on existing pressure taps on the line. Using these sensors in the field has the following limitations: the system must be shut down and depressurized to install the sensors, available pressure taps are rarely in the area of interest, pressure data can only be collected at a few test points, replacement of the sensor during operations is not possible, they can pose a hazard when employed in flammable environments as their pressure gauges are often electrical-based devices, and piping integrity might be compromised by the installation of the invasive sensors. Gas leakage from the transducer to pipe fitting is likely.

One approach to avoid these limitations is to implement a non-intrusive pressure sensing system using strain gages from the ‘breathing’ mode of the piping, which can be installed on the exterior of a pipe or vessel and does not require pressure taps, drilling of holes or mechanical attachments.

This indirect technique must be robust enough to reject the effects of other shell modes and bending. Several factors influence the ability to measure breathing mode responses accurately, including strain gage configuration options and data processing methods.

In this paper, finite element analysis (FEA) will be utilized to evaluate the effects of various parameters such as pipe wall thickness and boundary conditions on the relationship between strain measurement and internal pressure. The most reliable methods to collect strain data, process and calculate internal pressure will be presented.

Fibreoptic sensors provide excellent possibilities to measure strain on the piping either circumferentially or along the axis of pipe on a large number of test locations. In this project, fiber bragg grating (FBG) sensors will be used to measure strain.

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Surge valve flow-induced turbulence in a centrifugal unit

Wednesday, October 7
3:15 PM – 4:00 PM

During the startup process of a 40,000 HP centrifugal compressor unit, significant low-frequency vibration was observed on the piping and support structure. The shaking was significant enough that plant personnel shut down the unit after a few minutes. The highest vibration was observed when the hot recycle valve was open during unit startup.

Several rounds of structural modifications were implemented to improve the stiffness of pipe supports, with little to no effect on vibrations. Further investigation revealed that the root cause of the problem was a flow-generated pulsation (turbulence) in the hot recycle valve. The hot recycle valve was put in reverse orientation and vibrations and dynamic pressure were significantly lower at all test points compared to normal orientation of the valve. The valve’s normal orientation was in flow-to-open direction (flow tending to lift the plug), this configuration allowed the use of low-noise trims. The normal orientation of the valve maximized noise attenuation by allowing the expanding gasses to exit the valve trim and continue downstream.

With this valve orientation, and under certain conditions, a low-pressure zone adjacent to the valve seat ring is created. This low-pressure region detaches from the valve body wall, enters the free stream and forms a free eddy. The hollow cavity inside the valve plug can be another source of generating vortices and turbulence.

Putting the valve in reverse orientation changed the flow stream, removed the vortices, significantly reduced dynamic pressure at low frequencies and allowed the unit to operate without vibration issues.

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Reducing pipe strain to reduce vibration - application of a GMRC guideline

Thursday, October 8
9:00 AM – 10:30 AM

Pipe strain and flange misalignment can lead to higher-than-normal vibrations on piping configurations. The problem of high vibration due to pipe strain is more common on reciprocating compressor packages due to several factors: high dynamic forces that are part of normal operation, compact designs for equipment packages and improper piping assembly and installation processes.

The case study in this paper will describe the evaluation process of vibration and pipe strain on several reciprocating compressor installations. Field testing found high vibrations at several locations even though proactive measures were taken to conduct API 618 design studies. Field assessments showed an excessive amount of pipe strain on different components. Removing the pipe strain led to a reduction of the vibrations to acceptable levels.

The paper will present the field observations and analysis results as well as recommendations provided in the GMRC guideline to avoid vibration problems on reciprocating compressor installations.

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Week 2
Technology updates

8-minute technology updates and innovation presentations by Wood, ACI Services, HOERBIGER, SIEMENS, Southwest Research Institute, MIRATECH Group, AAA Technology & Specialties, EMIT Technologies, INNIO Waukesha Gas Engines, Solar Turbines, Monico Monitoring and Dow.

We will present:

  • One clamp to rule them all – part III
  • Torsional vibration monitoring kit

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Introduction to pulsation and vibration on reciprocating compressors

Monday, October 12
1:00 PM – 4:00 PM

This introductory short course is geared to entry and intermediate level engineers, technicians and other staff involved in the field operations, maintenance and design of compressor systems.

Attendees will learn about:

  • Common sources of vibration problems on piping, foundation, skids, vessels, crankshaft and small-bore attachments
  • Pulsations and their impact on piping vibration
  • Techniques to avoid mechanical resonance Design requirements for new and retrofit installations
  • Vibration guidelines
  • Basic commissioning and troubleshooting recommendations

We will discuss several real-life case studies and use video clips to illustrate and reinforce the concepts.

The presenters encourage the audience to raise application- and vibration-related questions to ensure an interactive session.

This course is a primer to the popular two-day GMRC training course “Compressor station vibration and the impact on cost, performance and reliability”.

The authors have significant vibration design and field experience from a wide range of applications, including pipelines, gas storage, offshore facilities and upstream compressors.

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Piping design practices for reciprocating and centrifugal pumps

Designers of pump packages and the associated piping system are generally familiar with centrifugal pump best practices that ensure a safe and reliable installation.

Reciprocating pump installations, however, require special design considerations beyond those typically included in a centrifugal pump installation design. An incomplete design basis for reciprocating pump installations can lead to costly remedial actions after commissioning, significant downtime or more serious problems which, if undetected, can lead to failures of pump components, requiring a major redesign of the pump installation.

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Resolution of expansion turbine rotordynamic instability at a compressed air energy storage facility

Renewables can provide economical carbon-free electricity, but due to inconsistent weather, power from solar and wind is intermittent. Technologies that can temporarily store electricity to firm-up the supply from renewables will allow electricity grids to meet energy demand with a lower carbon footprint. Hydrostor, a Canadian start-up that is storing energy by injecting compressed air into deep underground caverns, has designed systems that make compressed-air energy storage economically viable.

Excess renewable electricity is used to run compressors that inject air into underground caverns. When electricity is needed, the compressed air is expanded through turbines to generate electricity. A water injection system moderates the pressure in the cavern and allows the machinery to operate at consistent operating pressures.

This case study focuses on rotordynamic instability that was experienced on one of the expansion turbine stages during commissioning of a compressed air energy storage (CAES) facility in Ontario, Canada. The turbine which experienced the vibration is a two-stage, integrally geared, radial turbine powered by heated compressed air and coupled to a 1,800 kW induction generator. The turbine rotor is equipped with tilt-pad bearings and operates at 42,000 RPM.

Broad-spectrum sub-synchronous vibration was experienced on the rotor during the initial runs, which was determined to be due to aerodynamic instability. The vibration caused the turbine to trip prior to reaching the full power operating condition. Swirl brakes, a flow straightener in the turbine exhaust, and reduced bearing oil supply temperature were implemented during commissioning with limited improvements to rotor stability. The thrust balance pressure and resulting thrust load also showed only a minor influence on rotor stability.

The rotordynamic simulation model was then investigated to duplicate the field test results and determine potential design or operating changes to increase the stability margin. The original rotor model confirmed marginally stable results at the design operating conditions. However, subsequent analysis determined that start-up operating conditions resulted in reduced stability margin.

Experimentation in the field established that with careful control of the turbine inlet variable nozzles that manage mass flow and interstage pressures, as well as manual control of impeller thrust balance pressure, successful operation to full power could be achieved without a vibration trip. Ultimately, automation and tuning of turbine inlet nozzles and thrust balance pressure allowed the turbine to be routinely started and operated to full power while avoiding or quickly passing through unstable operation.

The rotordynamics model was also used to design a squeeze-film damper bearing to significantly improve the stability margin. The new bearing was procured, along with an optimized swirl brake, and these items are available as a precaution to be installed if stability problems reappear in the future.

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Related Pages

Machinery analysis  •   Field engineering and troubleshooting  •   Products  •   Rotating equipment reliability  •  

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