Dear expert,
-- First off all you have to inspect the area visually, there are so many reasons for a chances to failure of coating .
Only low DFT is not a basic reason .if on the surface spot failure found after application of coating , you have to verify the defected area . Near the defected area cross cut-test is mandatory as per standared .If large area coating
is pill -off you should to do the pull - off test( As per specified std).
The reason of coating failure as given below.
1- Poor surface preparation
2- surface contaminated due to presence of oil and grease.
3- chloride level up to acceptable range.
4-Incorrect mixing of paint and re-coating time interval not followed.
5 - curing reason
--
On Thu, Sep 27, 2012 at 4:10 PM, sevak hiren <hirensevak80@gmail.com> wrote:
Dear,
Standard: SSPC PA 2
5.2.1 Minimum Thickness: The average of the spot measurements for each 10 m2 (100 ft2) area shall not be less
than the specified minimum thickness. No single spot measurement in any 10 m2 (100 ft2) area shall be less than 80% of the
specified minimum thickness. Any gage reading may under-run by a greater amount. If the average of the spot measurements
for a given 10 m2 (100 ft2) area meets or exceeds the specified minimum thickness, but one or more spot measurements is less
than 80% of the specified minimum thickness, additional measurements may be made to define the non-conforming area.
5.2.2 Maximum Thickness: The average of the spot measurements for each 10 m2 (100 ft2) area shall not be more
than the specified maximum thickness. No single spot measurement in any 10 m2 (100 ft2) area shall be more than 120% of the
specified maximum thickness. Any gage reading may over-run by a greater amount. If the average of the spot measurements
for a given 10 m2 (100 ft2) area meets or falls below the specified maximum thickness , but one or more spot measurements is
more than 120% of the specified maximum thickness, additional measurements may be made to define the non-conforming
area. Manufacturers' literature may be consulted to determine if higher maximum thickness readings are allowable under
specific circumstances.
Also you can see ASTM D 1186
There may be no. of reasons for failure in test.
What was required DFT ?
What was the max DFT observed ?
What is the average DFT observed ?
For Proper Pull Off test refer ASTM D3359
Test Method A—An X-cut is made in the film to the substrate, pressure-sensitive tape is applied over the cut and
then removed, and adhesion is assessed qualitatively on the 0 to 5 scale.
Test Method B—A lattice pattern with either six or eleven cuts in each direction is made in the film to the
substrate, pressure-sensitive tape is applied over the lattice and then removed, and adhesion is evaluated by comparison with descriptions and illustrations.
Test Method A is primarily intended for use at job sites while Test Method B is more suitable for use in the laboratory.
Also, Test Method B is not considered suitable for films thicker than 5 mils (125μm).
On Wed, Sep 26, 2012 at 12:47 PM, Ramchandra vichare <vicharerke@indiatimes.com> wrote:Dear Experts;
with reference to the subject referred above please let me advise with documentary evidence about tolerances for Painted items when DFT is specified. Why paining fail in cross cut/peel-off test(Pl. ref photograph attached)? How to control the same?
Requested to advise
Regards
RK Vichare
--
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With kinds Regards
*********************
PRAVEZ ALAM
MATERIAL/PIPING INSPECTOR
SK E &C
Ruwais Refinery Expansion Project,
P O Box : 11780, Ruwais, Abudhabi.
United Arab Emirates.
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E-mail-skec.cv4087@partner.sk.com
"When I am working on a problem I never think about beauty. I only think about how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong."
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