Procedure for Evaluation in VIS-4

Posted on 15. Mar, 2009 by in NSRP

Procedure for Evaluation in VIS-4

When do you evaluate the Flash Rust?
 Flash rust and the substrate (surface) condition are evaluated at or before the time of painting. 
 Look at the Project Documents to determine the length of time that can lapse between inspection points and paint application.
 Plan your inspection of flash rust so that the paint can be applied during the time periods allowed by the project documents between the inspection points and application.

 If the surface conditions change between time of inspection and time of painting, then typically this Change is a “stop” or “hold” point.  This requirement that the substrate condition remain the same between inspection and application is true also for dry abrasive blasting. 

 Prior to painting, compare the flash-rusted surface with the flash rust photographs.
 Wipe or use tape as a further determination.
 Prior to painting, the degree of flash rust must be in accordance with the contract specifications.
Keep in mind that you are evaluating is the surface apparent or obscures, and what is the quantity of loose rust dust.  The coatings manufacturer makes the recommendation about the suitability of the coating system over the amount of clean flash rust.  If there is a doubt about interpretation, talk with an experienced field representative or the technical support group of the coating to be applied.

Caution: Do not develop a technique where you wipe like the dickens in order to prove the flash rust is unacceptable based on “the ease of removing a lot of color.“ Any rusted surface will transfer some brown color to a rag if it is scrubbed against the surface.

In addition, Hempel describes a pressure sensitive tape test as a quantitative measurement.  This manual provides detail of the wipe tests, and does not include details of the tape test as it is not included in the “standard” definition.
Four Ways to Lightly Wipe the Surface
 Wipe with hand **
 Wipe with cloth held in hand
 Wipe with cloth in a swatch
 Wipe with cloth around a brush

** SSPC SP-12 and VIS-4 describe the use of a cloth in the definitions.  While wiping with a hand is often done in the field, it should not be encouraged as the hand and fingers can leave a residue, such as sweat, on the substrate.

Different clothes might give different “pick-up” results.
Cloth will “stick” to the metal tips- so be consistent in the type of material. If lint deposition is a concern, consider other evaluation methods.
Consider using lint-free cloth wipes from laboratory supply

For example-Lint Free Wipes are available From VWR Laboratory Supply House
Laboratory cotton precut lint free cloth  VRW TWTX309,
Clean Room quality cotton replacement  VRW TWTX609,

Just using rags out of the rag bin will lead to trouble with interpretation.

The cloth used in wiping is to be DRY, not wet. .  This is not a heavy scrubbing with a cloth.
The flash rust is occurring so fast that it forms loose powder (dust); it does not crystallize or consolidate to form a rust barrier layer. The wiping is to determine the quantity of clean, loose rust dust.

Tags: , , ,

Leave a Reply