Issues with pipeline topcoats.
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Dear sea friends: There is a question – one of our company’s idle pipelines needs to be put to use now, as an N2 pipeline； Here’s the problem: the original topcoat for this pipeline is silver, while our company’s N2 pipelines use a yellow topcoat. How should this be handled in terms of construction? Is there any regulatory basis? Can I simply apply yellow topcoat directly over the existing pipe’s topcoat?
Conduct an adhesion test; if possible, apply a coat. Also, for the idle pipes, don’t you need to purge and pressure-test them first?
Is tape used in the adhesion test?
No, I’ve only heard about it; I can’t do it. I’m worried that the paint will chip after some time.
Just paint it directly; I once had a gas pipeline painted silver by mistake, and it was corrected later – no problems at all. If you have any questions, you can ask the construction workers directly; they are very experienced.
If it has been left unused for a long time, pollution is likely to occur; it can be sanded first and then coated with topcoat to improve adhesion
The adhesion of paint can only be determined indirectly. Currently, there are three main types of methods for measuring the adhesion of paint films: comprehensive measurement methods represented by the notch test and the scratch test; peeling test methods represented by the pull-off method; and water testing methods that involve the use of solvents and softeners.
Methods for testing paint adhesion: 1. First, use an art knife or a grid maker to draw a cross-shaped grid on the paint coating, making one cut in each direction to create 100 small squares, with each square measuring 1mm×1mm. The cut of the squeegee should reach the base coat of paint. 2. Use a brush to scrub in a diagonal direction five or six times each to clean away the small fragments, then apply tape to the cut and pull it away; the adhesive strength of the tape is 350–400 g/square meter. 3. Finally, observe the grid area under a magnifying glass. 4. The test results are in accordance with the testing standards for paint adhesion. Paint adhesion testing standards The criteria we use to determine paint adhesion are primarily the number of times the topcoat or plating layer is lifted off by tape, as well as the percentage represented per 100 squares. There are a total of five grades: 1. ISO grade: 5 = ASTM grade: 0B, which indicates that the peeling area of the paint is greater than 65%. 2. ISO grade: 4 = ASTM grade: 1B; some or all of the squares are peeled off, with the peeling area accounting for more than 35%-65%. 3. ISO grade: 3 = ASTM grade: 2B, indicating some peeling along the edge of the cut or extensive paint peeling; in some cases, entire sections of the pattern are peeled off, covering an area of more than 15%-35%. 4. ISO grade: 2 = ASTM grade: 3B, indicating that the area of chipping on the edges of cuts and intersections is greater than 5%-15%. 5. ISO grade: 1 = ASTM grade: 4B; this indicates that there is minor paint peeling at the intersections of the cuts, with the actual damage within the test area being less than or equal to 5%. 6. ISO grade: 0 = ASTM grade: 5B, which indicates that there is no peeling at the edges of the grid, and the edges of the cuts are completely smooth. This is the highest level of adhesion.
The workload is already considerable; repainting is required, along with repairing the damaged parts