Problem: Failure to conduct strength test and tightness test before valve installation causes leakage problems during use. Performance: Failure to conduct strength test and tightness test before valve installation, fail to find and deal with valve defects, affect normal use, and even cause valve leakage. Problem analysis: Although the valve has a factory certificate, it may be damaged by collisions, smashes, etc. after transportation, loading, unloading, and storage, which may cause cracks in the valve or failure or damage of the sealing packing. Affect normal use or rework and overhaul, resulting in labor and material consumption, which will cause valve leakage. Solution: In order to ensure the tightness and integrity of the valve and reduce rework, the valve must be tested for strength and tightness before installation. The following regulations should be followed. (1) Perform strength test and tightness test on valves according to pipeline engineering construction specifications. 10% (at least one) of the low-pressure valves shall be sampled, and the valves of high, medium pressure, toxic, highly toxic and Class A and B fire hazardous substances shall be tested one by one. (2) The strength test pressure of the valve should be carried out according to Table 5-17. Table 5-17 The nominal pressure of the strength test of the valve PN (MPa) The test pressure (MPa) Qualified standard ≤321.5PN test time is not less than 5min, shell and packing have no leakage as qualified 40565070649080100100130 Note: 1. When PNu003c1MPa, And the gate valve
with DNu003e600mm can not be subjected to strength test alone. The strength test is carried out during the pressure test of the piping system. 2. The strength test of the counter valve can be carried out during the system test. (3) Tightness test can be carried out at nominal pressure or at 1.25 times working pressure. The basis for determining whether it is qualified: the valve sealing surface is qualified, and the water-use cast iron and cast copper gate valve with PN≤2.5MPa is allowed to have a leakage not exceeding the amount of Table 5-18. Nominal diameter (mm) leakage (cm3/min) nominal diameter (mm) leakage (cm3/min)≤400.056001050~800.170015100~1500.2800202000.3900252500.51000303001.512005035021400754003≥6001005005 (4) Valves that have passed the test should be drained in time Water accumulates inside and blow dry. Except for the valves that need to be degreasing, the sealing surface should be coated with anti-rust oil, the valve should be closed, the inlet should be closed, and the 'valve test record' should be filled in according to the provisions of Table 5-19.
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