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Continued from The
Blog, p. 13.
The following items relate to coatings & linings.
Please be advised that the items are
not peer-reviewed, and opinions and suggestions are entirely those of the in- quirers and respondents. NACE Interna- tional does not guarantee the accuracy of the technical solutions discussed.
welcomes additional responses to these items. They may be edited for clarity.
Copper slag embedded in blasted surface
visual inspection, we found that the cop- per slag was embedded in the surface and could not be removed with high-pressure compressed air. We need to ensure the quality of paint work to achieve a dock- free life of 20 years. The coating to be applied is solvent-free surface-tolerant epoxy. What are the causes for the con- tamination? Is there any guideline or standard to refer to? What will be the consequences if the coating is applied over the existing blasted surface?
Q
should be made to remove it where pos- sible. Overcoating should not cause a problem, although it is not very satisfac- tory visually. The usual cause for con- tamination would be excess abrasive be- ing blown onto the surface in the vicinity of sprayed work.
and foreign matter are removed to the extent that only traces remain in the form of spots or stripes. The copper slag you are using is fracturing when it hits the surface, embedding itself in the steel. One
A A
40 MATERIALS PERFORMANCE April 2012
Your SA standard covers the surface, which should be free of contaminants and near-white where almost all mill scale rust
As a contractor, we used copper slag when it was not feasible to use chilled iron. Copper slag is a nonferrous abrasive, so attempts
The external side of a ship hull was blasted with copper slag to SA Standard 2.5. During the
cause of this may be too high an air pres- sure or poor-quality slag. I recommend changing your abrasive to garnet, which will not give you this problem. Another solution is to brush-blast the area with ilmenite to remove the slag. These alter- natives are expensive but much cheaper than a repaint.
requirement for cleaning is lower com- pared to the energy requirement for the abrasive blast that is causing high embed- ment. This would be a problem in a case where the application is critical and has a high expected service life. Copper slag to SA 2.5 has been used for a very long time quite successfully. Personally, I like to have a surface as well-prepared as pos- sible and would not like to compromise in this critical area.
A Epoxy definition
version) refers to it as a ge- neric type of two-pack paint
Q
binder. This standard lists a number of different paint systems and gives ex- pected durabilities in different environ- ments. In these lists, it distinguishes be- tween "epoxy" and "epoxy combination." The only description of epoxy combina- tion is that an example is "epoxy hydro- carbon resin," whatever that may be. According to Annex C, which gives
properties, epoxy combination has the same properties as epoxy with better acid resistance, but poorer resistance to solvents, heat, abrasion, and impact. It Q[ WVTa [XMKQÅML QV [M^MZM UIZQVM IVL industrial environments where it can be primer, mid-, or topcoat, and is applied \W I VWUQVIT LZa ÅTU \PQKSVM[[ WN µU 1\ Q[ VW\ [XMKQÅML NWZ QUUMZ[QWV WZ underground environments.
Does anyone know what the term "epoxy combination" means? ISO 12944, Part 5 (2007
Garnet has a blocky, sub-rounded shape, which reduces embed- UMV\ [QOVQÅKIV\Ta KWUXIZML \W some slags. Clearly, the energy
What could prevent epoxy combina-
tion as a generic form from being used for immersion service if detailed tests were carried out and it was recommended by the paint manufacturer?
bitumen.
a long history, including as a substitute for coal tar pitch in coal tar epoxies. Depend- ing on the resin and curing agent combi- VI\QWV[ \PMZM IZM [QOVQÅKIV\ IUW]V\[ WN [XMKQÅK XZWXMZ\QM[ \PI\ KIV JM OIQVML including the ones mentioned.
A A
good and bad combinations. If it passes certain tests, then you have to ask, which tests? Most major manufacturers use many of the same tests for immersion service, but for comparative purposes, you must be sure the products you are compar- ing have passed the same tests.
A Coating thickness
LZa ÅTU \PQKSVM[[ ,.< WN as opposed to a 63% volume solids coating to achieve 125 ,.<'
_PM\PMZ \PM \_W LZa ÅTU[ WN []KP XW\MV\QITTa different coating materials would perform in the same way is open to question.
Q A
NACE International, Vol. 51, No. 4
^WT- ! µU WN ^WT]UM [WTQL[ 0W_M^MZ
Will it require less ap- plication when using an 83% volume solids coating to achieve a
I am not sure I understand your question. The words "epoxy com- bination" in generic form leave open many possibilities for both
?Q\PW]\ TWWSQVO I\ [XMKQÅK XZWL- ]K\[ Q\ Q[ LQNÅK]T\ \W KI\MOWZQbM "epoxy combinations." However, the use of hydrocarbon resins has
I suspect the standard may be referring to the replacement for coal tar epoxy where epoxy is used in combination with synthetic
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