Case study on the protection of petrochemical spiral guide rails in wet gas tanks: Combined protective effect of coatings and corrosion inhibitors

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The combined protective effects of coatings and corrosion inhibitors were utilized in a newly constructed 10,000 m3 spiral-guided wet gas holder by a certain company; coating protection along with corrosion inhibition measures were applied. After more than 6 years of use, the results are as follows: 1. The application process and effectiveness of the protective coating – Depending on the degree of corrosion in different parts of the gas holder, various protection methods were used: for the inner walls, the process involved surface preparation → two coats of epoxy-iron oxide primer → three coats of epoxy-coal glass flake coating → two coats of epoxy-coal topcoat. The bottom surface is treated by mechanical sandblasting to achieve Sa2.5, with a total thickness of over 300μm. The construction process for exterior wall protection is as follows: surface preparation → two coats of special primer for high-weatherability composite coatings → three coats of intermediate coat for high-weatherability composite coatings → two coats of topcoat for high-weatherability composite coatings. For the parts of the bottom surface that are exposed to water, mechanical sandblasting is used for rust removal, with a quality standard of Sa2 1/2. For the outer walls of the bell-shaped cover that are not exposed to water, manual or electric wire brush grinding is employed, achieving a quality standard of St3. Internal wall inspection is carried out after 5 years of use (when changing the water in the gas holder). The paint coating on the inner wall surface remains as bright as before, with no signs of rusting or cracking; the adhesion, hardness, and scratch resistance tests show no changes compared to the quality at completion. Inspection of the outer wall showed no changes on its surface – there was no rusting or bulging of the paint coating. Upon checking for scratches, the paint coating remained tough and in good condition as before. Based on the inspection results, the expected service life of this paint film is over 8 years. Table 1 Test results before and after the use of the corrosion inhibitor
Test piece mass (g) | Immersion time (h) | Test piece surface area (mm²) | Corrosion rate v/g·m⁻²·h⁻¹ | Corrosion rate v₁/mm·a⁻¹ | Average corrosion rate v/g·m⁻²·h⁻¹ | Average corrosion rate v₁/mm·a⁻¹
10.36 | 0.367 | 7.529 | 19.78 | 10.335 | 50.3768
20.33 | 0.367 | 7.528 | 62.409 | 10.313 | 70.3523 | 0.3239 | 10.3638
30.14 | 0.367 | 7.512 | 36.333 | 10.308 | 70.3460
40.00 | 0.152 | 538 | 470.0000 | 0.067 | 0.0000 | 0.075
50.00 | 0.152 | 528 | 920.0000 | 0.066 | 0.0000 | 0.074 | 0.0000 | 0.088 | 0.0000 | 0.099
60.00 | 0.252 | 528 | 10.0000 | 132 | 0.0000 | 148

Note: 1, 2, and 3 represent tests without the use of a corrosion inhibitor; test pieces 4, 5, and 6 were tested with the corrosion inhibitor applied.
2. Effect of the corrosion inhibitor: Before putting this gas tank into use, approximately 30 kg of corrosion inhibitor was added, based on the capacity of the water tank, at a concentration of around 10 mg/L. After more than 5 years of use, there has been no significant change in water quality; it is odorless, the color of the water has not changed much, and there are no organic substances floating on the surface of the water, fulfilling the expected results.