One of the instruments we study in the CIP Level 1 Course is the ISO Surface Comparator Slab.
The comparators you will use in class are the ones referenced in ISO 8503 Part Two and Part Five, and the method is also described in ASTM D 4417 Method A. Here's all you need to know about that Instrument.
Put simply, comparators are a flat steel plate containing a number of reference surface profiles formed on a corrosion-resistant metal. These reference profiles are then compared to the freshly blasted surface.
Due to the speed of the test, this method is especially useful when you want to go from blasting to painting as quickly as possible to avoid flash rust, or when measuring in hazardous areas or electronic equipment is prohibited.
First, select the appropriate type of surface profile comparator.
There are primarily two types: type G representing profiles blast cleaned with a grit abrasive, and type S which stands for profiles blast cleaned with a shot abrasive.
Since a mix of shot and grit produce a peened profile, the Type S comparator should be used to evaluate a working mix.
With all loose dust and debris removed from the test surface, place the appropriate surface comparator against it and compare, in turn, the test surface with each segments of the comparator.
This can be done with the assistance of a magnifier if necessary. We recommended a 5X magnifier, which allows you to easily compare the surface with a single segment of the comparator in great detail.
If visual assessment proves difficult, the standard recommends a tactile assessment. In other words, touch it.
You can use the back of a fingernail or a wooden stylus held between thumb and forefinger (which would avoid the transfer of contaminants from your finger to the surface.)
Once you've assessed the profile against each segment of the comparator, you determine the grade. However, this is not a case of simply choosing which segment the profile is closest to - i's defined as follows:
Simply record your result and then test another area of the surface. If you require a less subjective method, there are other test methods that produce a numerical value, so you can be more objective when inspecting the surface profile.
It's not a secret you have to demonstrate your familiarity with the gauges to earn your NACE CIP and this gauge is no exception. Review the standards - ISO 8503-2 and ISO 8503-5, and ASTM D4417 Method A, and you'll be in good shape.