Hydrostatic pressure testing is a method used to test the integrity and strength of pipelines, specifically PE and PVC water and sewerage pressure pipelines. The purpose of hydrostatic pressure testing is to ensure that the pipelines can withstand the required pressure without any leaks or failures. The test involves raising the pressure in a controlled manner to the System Test Pressure (STP) and then monitoring the pressure decay after isolating the main. The acceptable limit of pressure loss over test time and test length is specified, and different materials have different allowable pressure loss rates. The test helps identify any leaks or weaknesses in the pipeline, ensuring its reliability and safety.

The process of chlorinization involves adding chlorine to water in order to disinfect it and kill any harmful bacteria, viruses, or other microorganisms. Chlorine is a commonly used disinfectant in water treatment due to its effectiveness in killing pathogens.

During chlorinization, chlorine is typically added to the water in the form of chlorine gas, sodium hypochlorite, or calcium hypochlorite. The chlorine reacts with the water to form hypochlorous acid, which is a powerful disinfectant. This hypochlorous acid then dissociates into hypochlorite ions, which continue to disinfect the water.

The amount of chlorine added during chlorinization is carefully controlled to ensure that it is sufficient to kill pathogens, but not so high that it poses a health risk to consumers. The chlorine concentration is typically measured in parts per million (ppm) and is regulated by water treatment standards.

After the desired contact time, which allows the chlorine to effectively disinfect the water, the process of de-chlorinization takes place. De-chlorinization involves removing or neutralizing the residual chlorine from the water before it is released into the environment or distributed for consumption.

De-chlorinization can be achieved through various methods, including:

1. Chemical de-chlorination: Chemicals such as sodium bisulfite or activated carbon can be added to the water to neutralize the chlorine and convert it into harmless compounds.

2. Aeration: The water can be exposed to air or oxygen, which helps to naturally dissipate the chlorine through the process of evaporation.

3. Filtration: Activated carbon filters or other types of filters can be used to remove chlorine from the water.

It is important to properly de-chlorinate the water before it is discharged into the environment, as chlorine can be harmful to aquatic life and ecosystems.