Hydro test is mandatory for pressure vessels and we see often test failure in many cases. This time we found the failure during the test due to heavy load and weak ground holding the equipment. At the stage of start, everything was fine however, the ground holding the equipment wasn’t solid enough and the ground finally collapsed. The weight of the pressure vessel including water was appx. 800 ton. But design engineer didn’t include the weight of water at design stage.
For an information, the necessary period of cement hardening is minimum 28 days. Normally after 3 days, people can work on the ground however inside of the structure is still including moisture. If something heavy is used on the ground before 28 days, cracks could be found. It wasn’t checked whether the test was done before 28 days since cement work had been completed. But I guess that the period of hardening was the one of the reason of failure too.