| Connect Follow us on Twitter Like us on Facebook
About | Subscribe | Advertise


G84 Standard Practice for Measurement of Time-of-Wetness on Surfaces Exposed to Wetting Conditions as in Atmospheric Corrosion Testing

All Standards | ASTM Standards
Search Standards

Click to Purchase and Download this Standard or Test Method

Revision Date: April 03, 2012
Updated On: April 04, 2012
Editorial Change:
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 develop relationships between TOW and levels of ambient relative humidity (RH), long term studies have been carried out to show that the TOW experienced annually by panels exposed under standard conditions is equivalent to the cumulative time the RH is above a given threshold value. This time value varies with location and with other factors. Probability curves have been developed for top and bottom surfaces of a standard panel at one location which show the probable times that a surface will be wet as a percentage of the cumulative time the relative humidity is at specific levels. If needed, it should be possible to develop similar relationships to deal with other exposure conditions.

(Back to all Standards)


Novetas Solutions
Abrasive Blasting near or over water?

100% Recycled Glass! NO Arsenic, Beryllium or other Toxic Metals! Great White Metal Finish and Safer than Slags! Call us at 866-775-6226

Axxiom Manufacturing
Schmidt Introduces
the New miniBRS

Reduced in size, it is incredibly easy to maneuver and operate! The perfect alternative to larger blast & recovery units when project space is limited.
Call 1-800-231-2085

Blastman Robotics Ltd.
Robotic Blast Cleaning

Replace manual blasting with new Blastman robot models. Contact us to boost your production and save costs!

Carlisle Fluid Technologies
Built for Tough Jobs

From Epoxies to Urethanes to other high solid coatings, the new Binks Airless 75 delivers a great finish using an ergonomic design. Visit for more information.

ABKaelin, LLC
ABkaelin, LLC

MONITORING-Environmental and worker monitoring CONSULTING & INSPECTION – Coatings, EHS, and compliance.

HoldTight Solutions Inc.

Our HoldTight®102 salt remover & flash rust
preventer prevents flash
rust by removing surface contaminants. Contact us
for your nearest distributor.
(800) 319.8802

Abrasives Inc.
Check our Prices for Blast Abrasives

Faced with higher abrasive costs? We invite you to call & check our rates on Black Magic® coal slag and other quality blast materials. Abrasives Inc. 800-584-7524

International WorkBoat Show

Clemco International GmbH
Global engineering-trusted solutions

For more than 70 years, Clemco has provided the highest quality blast equipment with a total commitment to comfort and safety.

Corrosion Probe, Inc.
From Detection to Correction

Corrosion Probe, Inc. has the Most Concrete Coatings Experience and Expertise. Contact us today at

Technology Publishing

The Technology Publishing Network

The Journal of Protective Coatings & Linings (JPCL) PaintSquare
Durability + Design Paint BidTracker

EXPLORE:      JPCL   |   PaintSquare News   |   Interact   |   Buying Guides   |   Webinars   |   Resources   |   Classifieds
REGISTER AND SUBSCRIBE:      Free PaintSquare Registration   |   Subscribe to JPCL   |   Subscribe to PaintSquare News
MORE:      About   |   Privacy policy   |   Terms & conditions   |   Site Map   |   Search   |   Contact Us

© Copyright 2000-2016, Technology Publishing / PaintSquare, All rights reserved
2100 Wharton Street, Suite 310, Pittsburgh PA 15203-1951; Tel 1-412-431-8300; Fax 1-412-431-5428; E-mail