PSI - Issue 33

Fabrizio Pittau et al. / Procedia Structural Integrity 33 (2021) 630–645 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2.1. Testing methods and performance thresholds As described in Section 3, the specimens are coated with four different materials. The test is carried out by progressively introducing nitrogen and evaluating the leakage. The gas is progressively insufflating, through the valve instrumented with pressure gauge, with a reduced pressure. The aim of this test is not to evaluate high pressure performing but to identify the leakage. The nitrogen is used as insufflating gas because it is very spread in nature (80% of the total volume of the atmosphere) and is widely used as an industrial inert gas. The nitrogen has the property to generate double or triple atomic bonds do not taking part to ambientes reactions. The presence of three covalent bond gives to the diatomic nitrogen molecule high stability. Liquid nitrogen is usually adopted as a refrigerant for freezing by immersion, for the transportation of food products, meds, vaccines, and for the stable storage of biological samples. Three steps of insufflation are identified: 1) The initial flowing, to introduce nitrogen and reaching a limited over pressure. 2) The stop of the supply, to evaluate the tightens. 3) Continuous supply to identify the leakage. These steps are repeated over time to evaluate the performance of the different type of protective layers. Leakage is identified with two instruments widely applied in the industrial facilities to found leaks: the leakage tests and the electronic nitrogen detectors (Fig. 5).

(a) (b) Fig. 5. Details of the set up: (a) Leakage tests, (b) nitrogen detectors.

3. Type of Coating and application The boxes are fully covered with four types of commercial products (Fig. 6). The commercial name is not referenced in this paper, but their main properties and the application procedure is here reported. Each coating has a specific surface preparation procedure. The different supplier produces clear indication also around the joints sealing and the entire treatment cycle is illustrated here. A detailed description of the composition of this coating is illustrated here.