ASTM G96-90(2018)
(Guide)Standard Guide for Online Monitoring of Corrosion in Plant Equipment (Electrical and Electrochemical Methods)
Standard Guide for Online Monitoring of Corrosion in Plant Equipment (Electrical and Electrochemical Methods)
SIGNIFICANCE AND USE
5.1 General corrosion is characterized by areas of greater or lesser attack, throughout the plant, at a particular location, or even on a particular probe. Therefore, the estimation of corrosion rate as with mass loss coupons involves an averaging across the surface of the probe. Allowance must be made for the fact that areas of greater or lesser penetration usually exist on the surface. Visual inspection of the probe element, coupon, or electrode is required to determine the degree of interference in the measurement caused by such variability. This variability is less critical where relative changes in corrosion rate are to be detected.
5.2 Both electrical test methods described in this guide provide a technique for determining corrosion rates without the need to physically enter the system to withdraw coupons as required by the methods described in Guide G4.
5.3 Test Method B has the additional advantage of providing corrosion rate measurement within minutes.
5.4 These techniques are useful in systems where process upsets or other problems can create corrosive conditions. An early warning of corrosive attack can permit remedial action before significant damage occurs to process equipment.
5.5 These techniques are also useful where inhibitor additions are used to control the corrosion of equipment. The indication of an increasing corrosion rate can be used to signal the need for additional inhibitor.
5.6 Control of corrosion in process equipment requires a knowledge of the rate of attack on an ongoing basis. These test methods can be used to provide such information in digital format easily transferred to computers for analysis.
SCOPE
1.1 This guide covers the procedure for conducting online corrosion monitoring of metals in plant equipment under operating conditions by the use of electrical or electrochemical methods. Within the limitations described, these test methods can be used to determine cumulative metal loss or instantaneous corrosion rate, intermittently or on a continuous basis, without removal of the monitoring probes from the plant.
1.2 The following test methods are included: Test Method A for electrical resistance, and Test Method B for polarization resistance.
1.2.1 Test Method A provides information on cumulative metal loss, and corrosion rate is inferred. This test method responds to the remaining metal thickness except as described in Section 5.
1.2.2 Test Method B is based on electrochemical measurements for determination of instantaneous corrosion rate but may require calibration with other techniques to obtain true corrosion rates. Its primary value is the rapid detection of changes in the corrosion rate that may be indicative of undesirable changes in the process environment.
1.3 The values stated in SI units are to be considered standard. The values in parentheses are for information only.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in 5.6.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G96 − 90 (Reapproved 2018)
Standard Guide for
Online Monitoring of Corrosion in Plant Equipment
1
(Electrical and Electrochemical Methods)
ThisstandardisissuedunderthefixeddesignationG96;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
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1.1 This guide covers the procedure for conducting online 2.1 ASTM Standards:
corrosion monitoring of metals in plant equipment under D1125Test Methods for Electrical Conductivity and Resis-
operatingconditionsbytheuseofelectricalorelectrochemical tivity of Water
methods. Within the limitations described, these test methods G1Practice for Preparing, Cleaning, and Evaluating Corro-
can be used to determine cumulative metal loss or instanta- sion Test Specimens
neous corrosion rate, intermittently or on a continuous basis, G3Practice for Conventions Applicable to Electrochemical
without removal of the monitoring probes from the plant. Measurements in Corrosion Testing
G4Guide for Conducting Corrosion Tests in FieldApplica-
1.2 Thefollowingtestmethodsareincluded:TestMethodA
tions
for electrical resistance, and Test Method B for polarization
G15TerminologyRelatingtoCorrosionandCorrosionTest-
resistance.
3
ing (Withdrawn 2010)
1.2.1 Test Method A provides information on cumulative
G59TestMethodforConductingPotentiodynamicPolariza-
metal loss, and corrosion rate is inferred. This test method
tion Resistance Measurements
responds to the remaining metal thickness except as described
G102Practice for Calculation of Corrosion Rates and Re-
in Section 5.
lated Information from Electrochemical Measurements
1.2.2 Test Method B is based on electrochemical measure-
ments for determination of instantaneous corrosion rate but
3. Terminology
may require calibration with other techniques to obtain true
3.1 Definitions—See Terminology G15 for definitions of
corrosion rates. Its primary value is the rapid detection of
terms used in this guide.
changes in the corrosion rate that may be indicative of
undesirable changes in the process environment.
4. Summary of Guide
1.3 The values stated in SI units are to be considered
4.1 Test Method A–Electrical Resistance—The electrical
standard. The values in parentheses are for information only.
resistance test method operates on the principle that the
1.4 This standard does not purport to address all of the
electricalresistanceofameasuringelement(wire,strip,ortube
safety concerns, if any, associated with its use. It is the
of metal) increases as its cross-sectional area decreases:
responsibility of the user of this standard to establish appro-
l
priate safety, health, and environmental practices and deter-
R 5 σ (1)
A
mine the applicability of regulatory limitations prior to use.
Specific precautionary statements are given in 5.6. where:
1.5 This international standard was developed in accor-
R = resistance,
dance with internationally recognized principles on standard-
σ = resistivity of metal (temperature dependent),
ization established in the Decision on Principles for the l = length, and
Development of International Standards, Guides and Recom- A = cross-section area.
mendations issued by the World Trade Organization Technical
In practice, the resistance ratio between the measuring
Barriers to Trade (TBT) Committee.
element exposed to corrosion and the resistance of a similar
1 2
This guide is under the jurisdiction ofASTM Committee G01 on Corrosion of For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Metals and is the direct responsibility of ASTM Subcommittee G01.11 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Electrochemical Measurements in Corrosion Testing. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved May 1, 2018. Published June 2018. Originally the ASTM website.
3
approvedin1990.Lastpreviouseditionapprovedin2013asG96–90(2013).DOI: The last approved version of this historical standard is referenced on
10.1520/G0096-90R18. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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G96 − 90 (2018)
reference element protected from corrosion is measured, to 4.2.3 The corrosion current density, i , can be converted
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compensate for resistivity changes due to temperature. Based to corrosion rate of the electrode by Faraday’s law if the
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