ASTM G96-90(2013)
(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. TEST METHOD A—ELECTRICAL RESISTANCE (1-6)4
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 and health practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in 5.6.
General Information
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Standards Content (Sample)
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Contact ASTM International (www.astm.org) for the latest information
Designation: G96 − 90 (Reapproved 2013)
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 D1125Test Methods for Electrical Conductivity and Resis-
tivity of Water
1.1 This guide covers the procedure for conducting online
G1Practice for Preparing, Cleaning, and Evaluating Corro-
corrosion monitoring of metals in plant equipment under
sion Test Specimens
operatingconditionsbytheuseofelectricalorelectrochemical
G3Practice for Conventions Applicable to Electrochemical
methods. Within the limitations described, these test methods
Measurements in Corrosion Testing
can be used to determine cumulative metal loss or instanta-
G4Guide for Conducting Corrosion Tests in FieldApplica-
neous corrosion rate, intermittently or on a continuous basis,
tions
without removal of the monitoring probes from the plant.
G15TerminologyRelatingtoCorrosionandCorrosionTest-
3
1.2 Thefollowingtestmethodsareincluded:TestMethodA
ing (Withdrawn 2010)
for electrical resistance, and Test Method B for polarization
G59TestMethodforConductingPotentiodynamicPolariza-
resistance.
tion Resistance Measurements
1.2.1 Test Method A provides information on cumulative
G102Practice for Calculation of Corrosion Rates and Re-
metal loss, and corrosion rate is inferred. This test method
lated Information from Electrochemical Measurements
responds to the remaining metal thickness except as described
in Section 5.
3. Terminology
1.2.2 Test Method B is based on electrochemical measure-
3.1 Definitions—See Terminology G15 for definitions of
ments for determination of instantaneous corrosion rate but
terms used in this guide.
may require calibration with other techniques to obtain true
corrosion rates. Its primary value is the rapid detection of
4. Summary of Guide
changes in the corrosion rate that may be indicative of
4.1 Test Method A–Electrical Resistance—The electrical
undesirable changes in the process environment.
resistance test method operates on the principle that the
1.3 The values stated in SI units are to be considered
electricalresistanceofameasuringelement(wire,strip,ortube
standard. The values in parentheses are for information only.
of metal) increases as its cross-sectional area decreases:
1.4 This standard does not purport to address all of the
l
safety concerns, if any, associated with its use. It is the R 5 σ (1)
A
responsibility of the user of this standard to establish appro-
where:
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. Specific precau- R = resistance,
tionary statements are given in 5.6. σ = resistivity of metal (temperature dependent),
l = length, and
2. Referenced Documents
A = cross-section area.
2
2.1 ASTM Standards: In practice, the resistance ratio between the measuring
element exposed to corrosion and the resistance of a similar
reference element protected from corrosion is measured, to
1
This guide is under the jurisdiction ofASTM Committee G01 on Corrosion of
compensate for resistivity changes due to temperature. Based
Metals and is the direct responsibility of ASTM Subcommittee G01.11 on
Electrochemical Measurements in Corrosion Testing. on the initial cross-sectional area of the measurement element,
Current edition approved Aug. 1, 2013. Published August 2013. Originally
the cumulative metal loss at the time of reading is determined.
approved in 1990. Last previous edition approved in 2008 as G96–90 (2008). DOI:
Metal loss measurements are taken periodically and manually
10.1520/G0096-90R13.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. 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 (2013)
or automatically recorded against a time base.The slope of the i
corr
corrosionrate 5 K EW (4)
1
curve of metal loss against time at any point is the correction ρ
rateatthatpoint.Themorefrequentlymeasurementsaretaken,
where:
the better is the resolution of the curve from which the
K = a constant.
1
corrosion rate is derived.
4.1.1 The electrical resistance of the metal elements being
4.2.4 Equivalent weight of an elem
...
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