ASTM G84-89(2012)
(Practice)Standard Practice for Measurement of Time-of-Wetness on Surfaces Exposed to Wetting Conditions as in Atmospheric Corrosion Testing
Standard Practice for Measurement of Time-of-Wetness on Surfaces Exposed to Wetting Conditions as in Atmospheric Corrosion Testing
SIGNIFICANCE AND USE
This practice provides a methodology for measuring the duration of wetness on a sensing element mounted on a surface in a location of interest. Experience has shown that the sensing element reacts to factors that cause wetness in the same manner as the surface on which it is mounted.
Surface moisture plays a critical role in the corrosion of metals and the deterioration of nonmetallics. The deposition of moisture on a surface can be caused by atmospheric or climatic phenomena such as direct precipitation of rain or snow, condensation, the deliquescence (or at least the hygroscopic nature) of corrosion products or salt deposits on the surface, and others. A measure of atmospheric or climatic factors responsible for moisture deposition does not necessarily give an accurate indication of the TOW. For example, the surface temperature of an object may be above or below both the ambient and the dew point temperatures. As a result condensation will occur without an ambient meteorological indication that a surface has been subjected to a condensation cycle.
Structural design factors and orientation can be responsible for temperature differences and the consequent effect on TOW as discussed in 4.2. As a result, some surfaces may be shielded from rain or snow fall; drainage may be facilitated or prevented from given areas, and so forth. Therefore various components of a structure can be expected to perform differently depending on mass, orientation, air flow patterns, and so forth. A knowledge of TOW at different points on large structures can be useful in the interpretation of corrosion or other testing results.
In order to improve comparison of data obtained from test locations separated on a macrogeographical basis, a uniform orientation of sensor elements boldly exposed in the direction of the prevailing wind, at an angle of 30° above the horizontal is recommended. Elevation of the sensor above ground level should be recorded.
Although this method does not develo...
SCOPE
1.1 This practice covers a technique for monitoring time-of-wetness (TOW) on surfaces exposed to cyclic atmospheric conditions which produce depositions of moisture.
1.2 The practice is also applicable for detecting and monitoring condensation within a wall or roof assembly and in test apparatus.
1.3 Exposure site calibration or characterization can be significantly enhanced if TOW is measured for comparison with other sites, particularly if this data is used in conjunction with other site-specific instrumentation techniques.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 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.
General Information
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: G84 − 89 (Reapproved 2012)
Standard Practice for
Measurement of Time-of-Wetness on Surfaces Exposed to
1
Wetting Conditions as in Atmospheric Corrosion Testing
ThisstandardisissuedunderthefixeddesignationG84;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope cellisfedthroughasignalconditioningcircuittoanindicating
or recording device. The objective is to record the time that
1.1 This practice covers a technique for monitoring time-
moisture is present on the sensing element during any given
of-wetness (TOW) on surfaces exposed to cyclic atmospheric
period. The fact that a potential is generated is critical to this
conditions which produce depositions of moisture.
technique.Aspertainstothispractice,theabsolutevalueofthe
1.2 The practice is also applicable for detecting and moni-
potential generated is essentially of academic interest.
toring condensation within a wall or roof assembly and in test
2.2 This practice describes the moisture-sensing element,
apparatus.
procedures for conditioning the elements to develop stable
1.3 Exposure site calibration or characterization can be
films on the electrodes and verifying the sensing-element
significantly enhanced if TOW is measured for comparison
function, and use of the element to record TOW.
with other sites, particularly if this data is used in conjunction
3. Significance and Use
with other site-specific instrumentation techniques.
3.1 This practice provides a methodology for measuring the
1.4 The values stated in SI units are to be regarded as
durationofwetnessonasensingelementmountedonasurface
standard. No other units of measurement are included in this
inalocationofinterest.Experiencehasshownthatthesensing
standard.
elementreactstofactorsthatcausewetnessinthesamemanner
1.5 This standard does not purport to address all of the
as the surface on which it is mounted.
safety concerns, if any, associated with its use. It is the
3.2 Surface moisture plays a critical role in the corrosion of
responsibility of the user of this standard to establish appro-
metals and the deterioration of nonmetallics.The deposition of
priate safety and health practices and determine the applica-
moistureonasurfacecanbecausedbyatmosphericorclimatic
bility of regulatory limitations prior to use.
phenomena such as direct precipitation of rain or snow,
condensation, the deliquescence (or at least the hygroscopic
2. Summary of Practice
nature) of corrosion products or salt deposits on the surface,
2.1 This practice describes a technique for detecting and
and others. A measure of atmospheric or climatic factors
recording surface moisture conditions. The moisture serves as
responsible for moisture deposition does not necessarily give
an electrolyte to generate a potential in a moisture sensing
an accurate indication of the TOW. For example, the surface
element galvanic cell that consists of alternate electrodes of
temperature of an object may be above or below both the
copper and gold, silver and platinum, or zinc and gold. The
ambient and the dew point temperatures. As a result conden-
spacing of the electrodes may be 100 to 200 µm, the width
sationwilloccurwithoutanambientmeteorologicalindication
dimension is not considered critical (Fig. 1). However, when
that a surface has been subjected to a condensation cycle.
zinc is used as an electrode material, the effects of the
3.3 Structural design factors and orientation can be respon-
hygroscopic nature of the corrosion products on the perfor-
sible for temperature differences and the consequent effect on
mance of the sensor should be kept in mind. Also, the use of
TOW as discussed in 4.2. As a result, some surfaces may be
copper as a sensor material should be avoided in sulfur
shielded from rain or snow fall; drainage may be facilitated or
dioxide-laden atmospheres to avoid premature deterioration of
prevented from given areas, and so forth. Therefore various
the sensor’s copper substrate. The output (potential) from this
components of a structure can be expected to perform differ-
ently depending on mass, orientation, air flow patterns, and so
forth. A knowledge of TOW at different points on large
1
This practice is under the jurisdiction ofASTM Committee G01 on Corrosion
structures can be useful in the interpretation of corrosion or
of Metals and is the direct responsibility of Subcommittee G01.04 on Atmospheric
Corrosion.
other testing results.
Current edition approved Jan. 1, 2012. Published March 2012. Originally
3.4 In order to improve comparison of data obtained from
approved in 1981. Last previous edition approved in 2005 as G84–89(2005). DOI:
...
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