Purge: sequence suggestion: high pressure >; & gt Low pressure, if you have the ability to have more than a few blowholes, you can have more, so it is easy to blow clean, although it is more troublesome to do. In areas where pipelines change rapidly (such as large pipelines and small pipelines), more purging is needed, and the purging effect shall be subject to the qualified blasting. It is suggested that the target should be made of strong wooden board, and the front of the target should be painted with white paint, which has the advantages of repeated operation and convenience.
Suppression (gas): sequence suggestion: high pressure >; & gt low pressure. The pipe sections with different pressure grades are pressurized separately, and after the high pressure is completed, the gas in the high pressure section is used in the low pressure section, which saves the cost. During pressing, carefully check the leakage point with soapy water. When soapy water is used, it is suggested that there should be no artificial bubbles when it is sprinkled on possible leakage points, so as to ensure the accuracy of inspection.
In the process of pressure holding-out, key equipment such as safety valve, pressure reducing valve and flowmeter do not participate in pressure test. You can turn it off first or bypass it.
Cold preservation: At present, there are two methods of cold preservation, one is pre-cooling before cold preservation, and the other is pre-cooling after cold preservation (all straight pipe sections are pre-cooled, and welds, pipe fittings and pipeline components are emptied before cold preservation). I prefer to precool first and then keep cold, so that I can check the installation quality of low-temperature pipes during precooling. Generally, the position where tensile cracks are most likely to occur in the process of cold preservation is the weld of pipe fittings.
Pre-cooling sequence: inlet pipeline (including unloading supercharger) > > low temperature storage tank >:> outlet pipeline (including self-pressurization pipeline) > > gasifier. If equipped with low temperature booster pump, it will be put in the last pre-cooling. During pre-cooling, keep away from non-operating personnel, and the operators can only operate after wearing protective measures. On the pipeline with low-temperature valve, the valve can be closed first to observe whether there is internal leakage at low temperature, and then let the cold air go down after it is normal.
Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.