ASTM G91-11(2018)

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: G91 − 11 (Reapproved 2018)
Standard Practice for
Monitoring Atmospheric SO Deposition Rate for
Atmospheric Corrosivity Evaluation
This standard is issued under the fixed designation G91; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope G140 Test Method for Determining Atmospheric Chloride
Deposition Rate by Wet Candle Method
1.1 This practice covers two methods of monitoring atmo-
G193 Terminology and Acronyms Relating to Corrosion
spheric sulfur dioxide, SO deposition rates with specific
2.2 ISO Standards:
application for estimating or evaluating atmospheric corrosiv-
ISO 9225 Corrosion of metals and alloys – Corrosivity of
ity as it applies to metals commonly used in buildings,
atmospheres – Measurement of environmental parameters
structures, vehicles and devices used in outdoor locations.
affecting corrosivity of atmospheres
1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
3. Terminology
standard.
3.1 Definitions—The terminology used herein shall be in
1.3 This standard does not purport to address all of the
accordance with Terminology and Acronyms G193.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
4. Summary of Practice
priate safety, health, and environmental practices and deter-
4.1 Sulfation plates consisting of a lead peroxide reagent in
mine the applicability of regulatory limitations prior to use.
an inverted dish are exposed for 30-day intervals. The plates
1.4 This international standard was developed in accor-
arerecoveredandsulfateanalysesperformedonthecontentsto
dance with internationally recognized principles on standard-
determine the extent of sulfur capture. Lead peroxide cylinders
ization established in the Decision on Principles for the
are also used for monitoring atmospheric SO in a similar
Development of International Standards, Guides and Recom-
manner. The results are reported in terms of milligrams of SO
mendations issued by the World Trade Organization Technical
per square metre per day.
Barriers to Trade (TBT) Committee.
2. Referenced Documents 5. Significance and Use
2.1 ASTM Standards:
5.1 Atmospheric corrosion of metallic materials is a func-
D516 Test Method for Sulfate Ion in Water tion of many weather and atmospheric variables. The effect of
D1193 Specification for Reagent Water
specific corrodants, such as sulfur dioxide, can accelerate the
D2010/D2010M Test Methods for Evaluation of Total Sul- atmospheric corrosion of metals significantly. It is important to
fation Activity in the Atmosphere by the Lead Dioxide have information available for the level of atmospheric SO
Technique when many metals are exposed to the atmosphere in order to
G16 Guide for Applying Statistics to Analysis of Corrosion determine their susceptibility to corrosion damage during their
Data life time in the atmosphere.
G84 Practice for Measurement of Time-of-Wetness on Sur-
5.2 Volumetric analysis of atmospheric SO concentration
faces Exposed to Wetting Conditions as in Atmospheric
carried out on a continuous basis is considered by some
Corrosion Testing
investigators as the most reliable method of estimating the
effects caused by this gas. However, these methods require
This practice is under the jurisdiction of ASTM Committee G01 on Corrosion
sophisticated monitoring devices together with power supplies
of Metals and is the direct responsibility of Subcommittee G01.04 on Corrosion of
and other equipment that make them unsuitable for many
Metals in Natural Atmospheric and Aqueous Environments.
Current edition approved May 1, 2018. Published June 2018. Originally exposure sites. These methods are beyond the scope of this
approved in 1986. Last previous edition approved in 2011 as G91 – 11. DOI:
practice.
10.1520/G0091-11R18.
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
Standards volume information, refer to the standard’s Document Summary page on Available from International Organization for Standardization (ISO), 1, ch. de
the ASTM website. la Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http://www.iso.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G91 − 11 (2018)
5.3 The sulfation plate method provides a simple technique within 120 days of their preparation, and if stored they should
to independently monitor the level of SO in the atmosphere to be kept in a cool dry location.
yield a weighted average result. The lead peroxide cylinder is
8. Exposure of SO Monitoring Devices
similar technique that produces comparable results, and the
results are more sensitive to low levels of SO . 8.1 In general, the level of atmospheric sulfur dioxide varies
seasonally during the year so that a minimal exposure program
5.4 Sulfation plate or lead peroxide cylinder results may be
requires four 30-day exposures each year at roughly equal
used to characterize atmospheric corrosion test sites regarding
intervals. In order to establish the atmospheric SO level at an
the effective average level of SO in the atmosphere at these
atmospheric corrosion test site which has not been monitored
locations.
previously, a program in which six 30-day exposures per year
5.5 Either sulfation plate or lead peroxide cylinder testing is
for a period of 3 years is recommended. More extensive testing
useful in determining microclimate, seasonal, and long term
may be desirable if large variability is encountered in the
variations in the effective average level of SO .
results. Thereafter, the location should be monitored with at
least four tests in a 1-year period every 3 years. If the
5.6 The results of these sulfur dioxide deposition rate tests
maybeusedincorrelationsofatmosphericcorrosionrateswith subsequent tests are not consistent with the initial testing, then
another 3-year program of six tests per year is required. Also,
atmospheric data to determine the sensitivity of the corrosion
rate to SO level. if a major change in the general area occurs in terms of
industrial or urban development, then six tests per year for 3
5.7 The sulfur dioxide monitoring methods may also be
years should again be carried out.
used with other methods, such as Practice G84 for measuring
8.2 In monitoring exposure sites, a minimum of four plates
time of wetness and Test Method G140 for atmospheric
chloride deposition, to characterize the atmosphere at sites or two cylinders shall be used for each exposure period.
8.2.1 Sites which have a significant grade or elevation
where buildings or other construction is planned in order to
determine the extent of protective measures required for variation should be monitored with at least two plates or one
cylinder at the highest elevation and two plates or one cylinder
metallic materials.
at the lowest elevation.
6. Interferences
8.2.2 Plates and cylinders should be exposed, if possible, at
both the highest and lowest level above the ground at which
6.1 The lead peroxide reagent used in the sulfation plates or
corrosion test specimens are exposed.
lead peroxide cylinders may convert other sulfur containing
8.2.3 Sites larger than 10 000 m shall have at least eight
compounds such as mercaptans, hydrogen sulfide, and carbo-
plates or four cylinders exposed for each period. In rectangular
nyl sulfide into sulfate.
sites on level ground, it is desirable to expose two plates or one
NOTE 1—Hydrogen sulfide and mercaptans, at concentrations which
cylinder at each corner.
affect the corrosion of structural metals significantly, are relatively rare in
most atmospheric environments, but their effects regarding the corrosion
NOTE 2—Some investigators have reported significantly higher sulfa-
of metals are not equivalent to sulfur dioxide. Therefore, if H S, COS, or
tion results at locations closest to the ground.
mercaptans are present in the atmosphere, that is, the odor of rotten eggs
8.3 Installation:
is present, the lead peroxide method must not be used to assess
8.3.1 Brackets shall be used to hold the sulfation plates
atmospheric corrosivity. It should also be noted that no actual measure-
ments have been made which would establish the correlation between securely in an inverted position so that the lead peroxide
atmospheric H S, COS, or mercaptan level and sulfation as measured by
mixture faces downward. The plate shall be horizontal and
this practice.
shall be placed so that it is not protected from normal winds
6.2 The inverted exposure position of the sulfation plate is
and air currents. The bracket design should include a retaining
intended to minimize capture of sulfuric acid aerosols and
clip or other provision to hold the plate in the event of strong
sulfur bearing species from precipitation. The lead peroxide
winds. The retainer clip may be made from stainless steel,
cylinder method may be more susceptible to capturing sulfuric
spring bronze, hard aluminum alloy (3003H19), or other alloys
acid aerosol particles. However, it should be noted that such
withsufficientstrengthandatmosphericcorrosionresistance.A
aerosols are rare in most natural environments.
typical bracket design is shown in Fig. 1.
8.3.2 For lead peroxide cylinders, each device shall be
7. Preparation of SO Deposition Monitoring Devices
exposed in a support similar to that shown in Test Method
G140 for chloride candles. Each cylinder shall be securely
7.1 Sulfation plates can be prepared according to the
method of Huey. The plate preparation method is given in mounted in a vertical position with a clamp or other device to
hold it securely against wind or other mechanical forces. A
Appendix X1. Laboratory prepared plates should be exposed
within 120 days of preparation. cover at least 300 mm in diameter shall be securely mounted
above each cylinder with a clearance of 200 mm between the
7.2 Lead peroxide cylinders can be prepared as shown in
top on the cylinder and the bottom of the cover.The cover may
ISO 9225. The cylinder preparation procedure is also shown in
also be rectangular or square with a minimum size of 300 mm
Appendix X2. Lead peroxide cylinders should be exposed
for the smallest dimension. The stand and cover assembly
should be constructed of materials that are not degraded by
atmospheric exposure for the expected duration of their ser-
Huey, N. A., “The Lead Dioxide Estimation of Sulfur Dioxide Pollution,”
Journal of the Air Pollution Control Association, Vol 18, No. 9, 1968, pp. 610–611. vice.
G91 − 11 (2018)
FIG. 1 Sulfation Plate Holder
in this test method in a 3-h period. Thereafter, conventional sulfate
8.4 A 30 6 2-day exposure period is recommended for
analysis can be employed, for example, by barium precipitation and either
either the plates or cylinders. At the conclusion of this period,
gravimetric or turbidimetric analysis (see Test Method D516).
the device shall be removed from the bracket or holder and
covered tightly to prevent additional sulfation. Analysis of the
9. Calculation
specimensshallbecompletedwithin60daysofthecompletion
of the exposure. The specimen identification, exposure
9.1 The sulfate analysis provides the quantity of sulfate on
location, and exposure initiation date should be recorded when
each specimen analyzed. This should be converted to an SO
the plate exposure is initiated. At the termination of exposure,
capture rate, R, by the following equation:
the completion date should be added
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