Erosion in Piping Systems

Computer-Based Training Module: Erosion In Piping Systems

October 2006

Effective December 6, 2006, this report has been made publicly available in accordance with Section 734.3(b)(3) and published in accordance with Section 734.7 of the U.S. Export Administration Regulations. As a result of this publication, this report is subject to only copyright protection and does not require any license agreement from EPRI. This notice supersedes the export control restrictions and any proprietary licensed material notices embedded in the document prior to publication.

2© 2006 Electric Power Research Institute, Inc. All rights reserved.

Introduction to Navigation

• Module can be navigated in a linear fashion

– Click Page Down or Enter.

• By following hyperlinks for more information– The file must be viewed in “Slide Show” mode for the hyperlinks to

work– Click on a hyperlink to go directly to related information in the

training, clicking page down or enter will take you back to where you left off.

• Click on the camera picture to view a related photograph, page down, or enter will return to the original page.


Introduction

• Mechanical damage is commonly found in piping systems.

• There are various mechanisms possible.

• They are normally combined under the category of “erosion” or “erosive damage.”


Turbine blades damaged by solid particle erosion.

Examples of Erosive Damage

Pump impellor damaged by cavitation.


Purpose

This module will:

• Introduce the subject

• Describe the four common mechanisms that cause damage in piping systems

• Discuss how these mechanisms cause damage, and

• Describe where damage is typically found.


Purpose - Continued

• Discuss inspection approaches, materials and countermeasures.

• This module will not treat damage in machinery, e.g., pumps, steam turbines.

• A short quiz is provided at the end of this module.


Erosion - Description

• Erosion is the damage of materials caused by physical processes such as high-speed, impinging flows or solid impacts on the surface.

• This is contrasted to corrosion which involves a chemical or electrochemical process.

• For more information on corrosion – go to corrosion.


Erosion – Description - Continued

• Erosion occurs in a variety of power-plant systems – see sample photographs.

• To successfully manage problems caused by erosion, the cause of the damage must be identified as there may be substantial differences between mechanisms.


Erosion Mechanisms

• The four most common erosion mechanisms in power plants are:

– Cavitation erosion

– Flashing erosion

– Droplet impingement

– Solid particle erosion

• These will be introduced


Photographs of Damage

Cavitation Erosion Flashing Erosion

Droplet Impingement Solid Particle Erosion photo courtesy of EDF photo courtesy of Bruce Power

photo courtesy of Florida Power & Light


Summary Table

Cavitation Erosion

Flashing Erosion

Droplet Impingement

Solid Particle Erosion

Fluid Conditions

WaterWater U/S 2-phase D/S

Two-PhaseSingle or two

phase

Surface Very roughSmooth – polished

Very rough Variable

Noise -

VibrationYes Yes No No

Damage rate Non-linear Non-linear Non-linear Linear

D/S = Downstream

U/S = Upstream


Types of Erosion Damage

For more information:

• Cavitation erosion -- see

• Flashing erosion -- see

• Liquid droplet impingement -- see

• Solid particle erosion -- see.


Other Related Mechanisms

• There are other types of damage that may be experienced:

– Corrosion and erosion may occur simultaneous (see next slide)

– Erosive effects may also be combined

– Other erosion mechanisms.


Photograph of Corrosion and Erosion Damage

Elbow Damaged by Erosion and FACphoto courtesy of Public Service Electric & Gas


Other Erosion Mechanisms

• Wire drawing – high speed liquid flow normally encountered in valve internals.

• Steam cutting – high speed steam flow normally occurring in valve seats or when leaks occur in heat exchangers.


Photographs of Damage Caused by Steam Cutting

Steam cutting in a steam trap body

Steam cutting in a flange


For More Information

• CHUG website

– User experience

– Past presentations on erosion.

• EPRI Report 1011231.

• EPRI Report TR-108943-V2.


Quiz

Question 1Droplet impingement and solid particle erosion are similar in many ways.

True False

Question 2There are materials that are more resistant to cavitation erosion than carbon steel.

True False


Quiz - Continued

Question 3In order for cavitation to occur the downstream pressure must be less than the local vapor pressure.

True False

Question 4In order for flashing to occur the downstream pressure must be less than the local vapor pressure.

True False


Quiz - Continued

Question 5Data sets are available to describe cavitation in:

a) Valvesb) Orificesc) Valves and orificesd) Elbowse) Nearly every situation

Question 6Models to calculate the rate of droplet impingement are commonly used to determine susceptibility of components in piping systems.

True False


Quiz - Continued

Question 7

Flashing erosion and droplet impingement often occur in high pressure drop situations.

True False

Question 8

Solid particle erosion has been found to have

a) A damage rate that is linear with time.

b) A damage rate that varies linearly with velocity

c) A damage rate that is independent of the particle size

d) A well understood damage mechanism

e) All of the above


Quiz - Continued

Question 9

Noise and vibration associated with a valve indicate that cavitation erosion is occurring.

True False

Question 10

The critical velocity for damage caused by droplet impingement is much greater than the critical velocity for solid particle erosion.

True False


Training Complete!

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This report describes research sponsored by the Electric Power Research Institute (EPRI).

The report is a corporate document that should be cited in the literature in the following manner:

Computer-Based Training Module on Erosion in Piping Systems. EPRI, Palo Alto, CA: 2006. 1013570.

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Erosion in Piping Systems