Stainless steel cleaning for blue spot testing
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Question: What is an appropriate area for each test point when performing the blue spot test on stainless steel after cleaning?
The blue dot test is a method for evaluating the quality of acid washing and passivation on stainless steel surfaces; its principle is to detect whether there is iron ion contamination on the surface of the stainless steel. The inspection ratio is determined by the design drawings; for critical equipment, the inspection ratio is 100%, while for ordinary equipment it is at least 5%.
For example: I have 100 pipes that need to be tested using the blue-dot method; can 5 of them be selected for testing? Is that what it means? Also, when conducting the blue dot experiment, what area did I use on a stainless steel pipe? The larger the area, the higher the probability of blue dots appearing, of course!
For the 5 samples drawn, 100% of the area of each one is used for testing.
Is that how it’s done? The pipes are quite long, 6 meters each – do both the inner and outer walls need to be treated?
The blue dot test is a method for evaluating the quality of acid washing and passivation on stainless steel surfaces; its principle is to detect whether there is iron ion contamination on the surface of the stainless steel. The inspection ratio is determined by the design drawings; for critical equipment, the inspection ratio is 100%, while for ordinary equipment it is at least 5%.
Follow these steps: prepare a solution by using 1 gram of erythrite plus 3 milliliters of 65–85% HNO3 plus 100 milliliters of water. Soak filter paper in this solution and then attach it to the surface to be tested; alternatively, the solution can be applied directly to the surface. If the passivation layer on the surface is imperfect or if there is iron ion contamination, a blue color will appear. If no blue dot appears within 1 minute, it is considered qualified.