Hydrostatic testing, and consequently de-watering are vital operations needed to be performed on pressurized pipelines. Both processes however, are associated with a number of potential hazards and risk. The following considerations and precautions should be taken when engaging in hydrostatic testing or de-watering.

Hydrostatic Testing

Hydrostatic testing should always be conducted after installation, and it is recommended to conduct testing throughout the duration of its expiry.  Hydrostatic testing is performed to assess the operational integrity of the piping. Operational integrity refers to the risks associated with the product in question, and assesses potential hazards that could arise.

Testing is performed by pumping water into the pipeline, and then consequently testing different levels of pressure for set periods of time. 

After testing has finished, the water in the pipeline must be removed, in a process known as de-watering. De-watering a pipeline involves adding an alternate line to the piping, and forcing a pig down the pipeline with large amounts of compressed air. A pig is a tool that fits into pipelines, and can be used for a variety of different processes. In the case of de-watering, a pig directs the water in the main piping to be redirected and consequently removed through the added secondary pipeline.

Hazards associated with de-watering

The process of de-watering pipelines has the potential for serious injury, and can even result in death. When the pig is pumped into the main pipeline, this can create huge variations in pressure.  These variations in pressure result from the changing velocity of the pig, which can result in wildly fluctuating air pressures. The air pressure created from the pig being pumped into the main pipeline can easily exceed that of the working pressure of the piping, resulting in the secondary pipe detaching from the main line. It is imperative that the secondary de-watering line is securely anchored in place before conducting the de-watering process.  When anchoring secondary waterlines, consider the potential for air pressure to exceed the capabilities of the main line, opting for strong anchoring that can withstand high air pressures.

The secondary de-watering line can come loose for several reasons, notably; worn couplings, fittings, and over-sights from operators. Couplings are used to attach the secondary pipeline to the main piping. When worn, couplings can come loose, resulting in the separation of the two pipelines.  It is imperative that couplings possess the required working pressure, and be properly fitted before being used in the de-watering process.

Fittings, such as turns and corners in the pipeline, contribute to the fluctuating pressures in the pipe, as when the pig is propelled through the main pipe, the pigs' velocity will increase or decrease. When planning hydrostatic testing and dewatering, take special note of any changes in direction within the main pipeline, and consider securing and anchoring these locations.

In Summary

While it is impossible to fully negate the risks of hydrostatic testing and de-watering, with careful planning and consideration towards specifics in the pipeline, risks and hazards can largely be negated.