Pipeline Hydrostatic Testing Explained

Pipeline Hydrostatic Testing Explained

Pipeline Hydrostatic testing is a vital procedure in both pipeline construction and pipeline maintenance. Before new pipeline runs go into operation, it is necessary to make sure they are correctly commissioned for their purposed use. Also, proper maintenance of pipelines requires that any pipeline susceptible to failing and leaking be caught during controlled testing procedures, not while fuels and other chemicals may be flowing through the pipes.

Industries have many vessels that routinely undergo high-pressure processes. These include gas cylinders, boilers, evaporators, and pipelines through which the fluids flow. The fluids can be gas or liquid, including water, natural gas, or even some highly corrosive chemicals like hydrochloric acid, sulfuric acid, and potassium hydroxide among others. There is always a specific range of pressure for a pipeline to transport fluid from one place to another, or for vessels to operate. Even if there is a minor leakage in the pipeline, it leads to pressure loss and potential environmental contamination.

You can observe the water leakage in the picture given below (Figure 1). This leakage took place because of the crevices in the pipeline. It either stops the transfer of water from one place to another or reduces the pressure to a great extent. So, to gauge the strength, performance, and durability of a pipeline, it is necessary to perform hydrostatic testing of the pipe.

Figure 1: Pipeline Hydrostatic Pressure Testing Failure

What Is Pipeline Hydrostatic Pressure Testing?

First, let’s define what pipeline hydrostatic pressure testing is. A pipeline, whether it be a petroleum pipeline or water supply pipeline, needs to be free from defects and leakage points so that it can withstand the required pressure. Pipeline hydrostatic testing ensures that the weld joints and flanges that join the pipes are fitted properly by the fitters, and the fluid doesn’t leak out of the pipe. It also ensures that the material used in the pipeline has the required tensile strength to sustain the pressure. In short, it ensures that the pipeline is suitable for use in reliably serving its objective.

Pipeline hydrostatic pressure testing is performed by charging the pipeline and then shutting off the supply valve for documenting observations about the pressure loss. This hydrostatic test is a pre-commissioning and non-destructive test or quality control procedure which authenticates the integrity of the pipeline and the fabrication, as well as the welding and joint jobs performed on it. Industries also execute it in the operational plants during shutdowns as a part of the regular maintenance procedure.

Criteria for Water Used in Pipeline Hydrostatic Pressure Testing

Using unfiltered or impure water from a lake or pond without any treatment for pipeline hydrostatic pressure testing has the possibility of damaging the pipeline. The pipe is not going to corrode immediately, but in the long run, if contaminated water flows in the pipeline in each hydrostatic test, then it can cause corrosion and subsequently lead to leakages. So, it is critical to use uncontaminated and treated water.

Typically, it is not possible to get a pure water supply while working on a construction site, fabrication yard or an operational unit. So, the water used in hydrostatic testing should be as close to potable as is feasible. Below is the general specification for potable water. Adherence to these specs are not entirely required, but preferred:

  • Percentage of Hydrogen (pH): pH should not be less than seven because low pH acid waters accelerate corrosion due to hydrogen ions. Maintaining the pH of the water used for testing between 7 and 8.5 is necessary.
  • Water Hardness: It is ideal to maintain it between 150 and 200ppm, but 300-400ppm is also acceptable for hydrostatic testing.
  • Calcium Hardness: Calcium (Ca) hardness should not be more than 80ppm.
  • Magnesium Hardness: Magnesium (Mg) below 40ppm is acceptable.
  • Iron Content: Iron (Fe) content should not more than 0.3ppm
  • Turbidity: 10 to 20ppm is allowed, but beyond that is unmistakably too impure to use for pipeline hydrostatic pressure testing.
  • Total Suspended Solid: TSS should be strictly NIL.
  • Temperature: The temperature of the water used for hydro-test should not be less than 17 degrees Celsius.

In layman language, the water used for hydrostatic testing should be close to potable. Generally, industries maintain a table or checklist and an authorized quality assurance department personnel authenticates water contents before the test begins. This choice of water also varies from the type of pipe under observation, its material composition, and its operational parameters.

Pipeline Hydrostatic Testing Equipment

Pipeline hydrostatic testing equipment should be preplanned and readied before the testing job date arrives. Pressure testing on any vessel will entail the availability of essential equipment. Here is the list of pipeline hydrostatic pressure testing equipment:

Pump, Valves, Couplings and Pressure Gauge – A pump which is capable of generating the specified design pressure of the pipeline is required for hydro-testing. The motor of the pump should have the power to generate the design pressure. However, the rating of the pump will be dependent on the pipe under observation and at what pressure it will be routinely operated. The setup should have a pressure gauge for measuring the pressure inside the pipe. The type of valve used varies as per the size of the pipeline. Couplings should be used to connect pipes in a best possible manner to eradicate any pressure drops.

Hydra or Crane – The pipelines can be as massive as 120 inches in diameter and even more dependent on the volume of liquid passing through it. So, transportation equipment like Hydra and crane should be used to lift and place the pipeline on the support or a designated place. It is necessary that the safety department certifies the belt and riggers handling the pipes and that only certified and competent executives operate the Hyrda or crane.

Support for Pipes – Sometimes hydro testing is performed on the sites, but many companies prefer to execute it at a space near the fabrication yard so that any anomalies can be ameliorated immediately. It is necessary to choose proper support, stand or sleepers to suspend pipes before hydrostatic tests start. The stands should be able to withstand the weight and length of the pipeline.

As you can see in figure 2, the pipes are placed on the stands, and the pump and pressure gauge is ready, which makes up for a complete hydro test setup. However, care needs to be taken in transporting the pipe from the testing facility to its designated location of use so as not to get any deformities in the pipe after testing.

Figure 2 - Hydrostatic testing equipment

How to Perform Pipeline Hydrostatic Pressure Test

Now to discuss how to perform pipeline hydrostatic pressure tests. Like all other quality assurance processes in industries, pipeline hydro-testing has a standard operating procedure (SOP). Here are the steps that need to be followed for a hydro-testing of pipelines:

Figure 3 - Simplified PFD for pipeline hydrostatic pressure testing

Now to discuss how to perform pipeline hydrostatic pressure tests. Like all other quality assurance processes in industries, pipeline hydro-testing has a standard operating procedure (SOP). Here are the steps that need to be followed for a hydro-testing of pipelines:

Equipment Setup and Pressure – Once the pipeline hydro testing equipment is tested and ready for use, raise the pressure in the pipeline to the test pressure. It should be slightly more than the pressure specified in the actual procedure of the process. Section ASME B31.8 stipulates the factors associated with test pressure including the allowable rate of increase or decrease. It is necessary that there should not be external air in the pipeline during the hydrostatic pressure testing. The air content can be evaluated by observing the change in pressure. This calculation provides the precise data about the changes that should be made in the pipeline, which helps during revamp jobs.

Inject the Water – Water as per the standards mentioned above should be used for hydrostatic inspection. This water should be injected at the specified pressure, volume, and temperature.

Calculate Performance Verification Testing Results for the Pipeline – PVT (Performance Verification Testing) results should be obtained which include aspects of pressure, volume, and temperature that vary from the kind of fluid flowing through the pipeline. A calibrated pressure and temperature recorder should be used.

Record the Observation – The pressure should be recorded at regular intervals. If the pipeline is flexible, the hydrostatic testing time should be raised to as much as 12 to 24 hours. The time varies from company to company based on the specification documented in SOPs.

Pipeline Hydrotesting Services

Pipeline hydrotesting services are simply part of pipeline installation and operational costs. All major pipeline owners and operators recognize, not just the value, but the necessity of performing these hydrostatic pressure tests. Hanging H Companies is skilled and experienced in pipeline hydrostatic testing services, with a long track record of successful hydrotesting jobs.

It is also advisable for engineers working on a pipeline to take an NDT (Non-destructive Testing) training course. The NDT course certifies them as authorized personnel who can approve or disapprove results obtained from hydrostatic pressure testing.

Pipeline or any vessel used without hydro testing will not only increase the maintenance cost but also cause safety perils in the plant. A running plant is clustered with a myriad of pipelines, through which some hazardous chemicals or high-temperature fluids also flow. A minor leakage can cause severe injuries or even fatalities. So, pipeline hydrostatic pressure testing is a crucial part of a quality assurance procedure ensuring reliable and safe operations of the pipe.

For a list of all of Hanging H’s core services, please see our services page. Not only do we provide hydro testing services, but we also offer all the main pipeline construction and maintenance services, including facility construction and maintenance.

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