Blue dot method testing standards and acceptance criteria
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After acid washing and passivation of the stainless steel surface, design documents typically require testing using the blue spot method, with the absence of blue spots indicating compliance; however, no standard methods for this testing are specified. The relevant standard that can be found is GB/T 25150-2010 \"Test methods for the quality of passivation films on austenitic stainless steel in chemical cleaning of industrial equipment – Blue spot method\". However, the testing procedure specified in this standard is as follows: 8.2 On-site testing of passivation film quality – 0.1 mL of the blue spot solution is dropped onto the selected metal surface using a 0.5 mL glass syringe; a stopwatch is started, and timing stops when 8 blue spots appear within the area covered by the solution. So the evaluation criterion is time, rather than “no blue dots,” but I have never seen any design documents specify a time requirement for passing the blue-dot test. How do fellow professionals in the field control the quality requirements after acid cleaning and passivation during the design and manufacturing of pressure vessels?
I remember that many requirements state that it is considered successful if no blue dots appear within 30 seconds.
What are the requirements for preparing the blue dot solution, selecting the testing location, cleaning the testing surface, and the number of testing points? Are there any standard requirements?
What are the requirements for preparing the blue dot solution, selecting the testing location, cleaning the testing surface, and the number of testing points? Are there any standard requirements?
This post was last edited by Exterminate demons and evil forces on 2017-4-10 08:17. Yes. There are no requirements at the moment. We all follow the following 2 criteria. Another is stipulated in Article 12.1 of \"HG20584-2011 Technical Requirements for the Manufacturing of Steel Chemical Containers – Explanatory Notes.\"
No relevant standards have been found for the blue-spot testing of pressure vessels; only a formula for the testing solution is provided in the compilation instructions for HG 20584.
Article 12.1 of HG/T 20584-2011 \"Technical Requirements for the Manufacturing of Steel Chemical Containers\": The quality of surface pickling and passivation can be inspected using the blue spot method as needed. There are no testing methods or acceptable criteria. Article 10.1 of HG 20584-1998 \"Technical Requirements for the Manufacturing of Steel Chemical Containers\": The quality of surface pickling and passivation can be checked using the blue-spot method if necessary. A solution is prepared by mixing 1 gram of erythrite with 3 milliliters of 65%–85% HNO3 and 100 milliliters of water; after soaking filter paper in this solution, it is applied to the surface to be tested, or the solution can be applied directly to that surface. If the passivation layer on the surface is incomplete or if there is iron ion contamination, a blue color will appear. The formula for the blue-dot liquid here differs from GB/T 25150-2010, and there are no specified testing ratios or acceptance criteria. From a design perspective, what constitutes excellence?
The explanatory notes for HG/T 20584-2011 state: 12.1.4 The formula of the testing reagent should not be specified rigidly, hence it is included in the explanatory notes. So, who determines the reagent formula?
It’s very difficult for designers alone to answer this question, after all, designers rarely engage in actual inspection work. However, pickling and passivation are not complicated processes either; a complete passivation layer is formed in the end, and if no blue spots are detected, it is considered qualified.
Yes, the standard requires blue dot testing, but there’s no implementation standard, which is really tricky!
If there are no specific method standards, it’s simple to prevent blue dots from appearing, and the testing becomes a mere formality.