Before any pipeline is put into commission, a hydro test is crucial as it helps gauge the strength and pressure resistance of the piping system. Even systems already in operation are subject to these tests. During maintenance shut-downs, pipelines, and their flanges and joints are often subject to hydro testing to prevent risks of leaks and system failures.  

What is Hydro Testing?

Also known as hydrostatic testing, hydro testing is a non-destructive method of checking equipment, particularly piping, for potential leaks and ruptures. This process is used to monitor the strength and pressure integrity of pipes with the help of special equipment. 

This testing uses a pressure-based system to check the expansion rate of pipes under pressure. If the hydrostatic test gauge shows a low-pressure resistance, it is an indicator of the low structural integrity of the pipeline. Consequently, a high-pressure reading shows that the piping is less prone to leakage and ruptures. 

As mentioned, both new and existing pipes are subject to this test. Hydrotesting helps monitor the piping system for 

• Potential stresses in the pipelines
• Leakage is caused by weak welds and flange joints.
• The potential rupture caused by the low structural integrity of the piping system.

How Does Hydrotesting Work?

Though water is the primary testing medium used in hydro testing, manufacturers may sometimes opt for high-pressure gas to test leaks in their piping systems. But in most cases, water is pumped into the pipe using high-pressure jets and hoses to conduct this test. This step helps expel the air contained inside the structure. The water inside the pipe is injected at about 166.6%, 143%, or 150% of the pipe’s designed working pressure.

This pressure within the pipe is maintained for some time. It is common for pipe manufacturing companies to use colored dyes in the water to detect leaks better. Red or fluorescent dyes may be added to the liquid before it is injected into the pipes. If there is a leak in the structure, this colored water makes it easier to detect the cracks. 

Manufacturers follow the ASME B31.3 specifications when testing oil and gas pipeline pipes. These standards lay down the requirements for the

• Design pressure of the pipe
• The structural integrity of the pipe.

According to the ASME B31.3 specification, the water pressure within a gas pipeline during hydro testing must be at least 125% of its maximum allowable working pressure. 

Tools Used in Hydro Testing

• High-Pressure Pump: Crucial to inject water inside the test models
• Hose Systems: Used to transport water from the source to the pump
• Pressure Gauge– To check the pressure reading within the pipe. Its range must be 150% to 400% of the hydro test pressure. Their calibration must also be under a year old. 
• Pipe Supports: Used to hold the pipe in place during hydro testing
• Test Medium – Water, in most cases
• Temperature Gauges – To read/maintain the necessary temperature required fro testing
• Torch/Flash – To check the external surface of pipes for leakage 
• Torque Wrench: To tighten bolts and joints

Conditions Required for Hydro Testing

Water Conditions Required for Hydro Testing

Factor	Required Setting
Water Temperature	Should not be less than 62.6 Degrees Fahrenheit
Iron Content in Water	Less than 0.3 ppm
Magnesium Hardness in Water	Less than 40 ppm
General Water Hardness	150 ppm to 400 ppm
Calcium Hardness on Water	Below 80 ppm
Contaminants/Suspended Solids	Absent
Water Turbidity	Between 10 ppm to 20 ppm
Hydrogen in Water	7% to 8.5%

*Using contaminated/untested water can potentially disrupt the hydrostatic testing and can even lead to pipe damage. Pollutants in the liquid may react with the steel, causing corrosion and leakage down the line. To avoid such issues, the water used for hydro testing should conform to the above conditions.

Pressure Conditions Required for Hydro Testing

Though ASME specifications are typically the norm in hydrotesting operations, the standards for this process may change depending on the type of piping produced. The general pressure-based conditions and specifications used for hydrostatic testing of pipes are as follows

Specification	Piping Type	Required Pressure
ASME B31.1	Energy-Based	150%
ASME B31.3	Manufacturing/Production-Based	150%
ASME B.31.9	Construction Based	150%
ASME I	Boiler Pipes	150%

Types of Hydro Testing

Depending on the type of pipe tested. Hydrptesting may be categorized into two major types. The following methods are generally used to monitor smaller pressure models' defects and structural integrity. 

Direct Expansion 

The readings taken in this model of pressure testing is based on three major readings, viz

• Amount of water injected into the pipe
• Amount of water expelled 
• The test pressure used 

A straight-forward model, in direct expansion, high powered hoses deposit water into pipes at a specific pressure for a fixed period. During this time, water is expelled from the test model, which is then used to measure the total expansion rate of the pipe. If adequate, the batch of piping can then be successfully marked for service. 

Water Jacket Method

This method follows the same first few steps as the previous model. As with the direct expansion system, water is injected into the pipe at high pressure. However, instead of using the water expelled to test the pipe’s expansion values, in the water jacket method, the structure is loaded into a water-sealed chamber known as the test jacket. 

Within the chamber, the pipe is exposed to high pressure for about 3 seconds. As a result of this compression, the piping expands, causing water to be displaced into a test tube connected to the test jacket. The amount displaced is measured to discover the pipe expansion.

Once complete, pressure within the test jacket is reduced, causing the pipe to return to its original size. The water displaced indicates the piping’s pressure resistance - the lesser the amount, the higher the model's structural integrity. 

In addition to these modes, manufacturers may use gas instead of water to test the structural integrity of pipes. As with their liquid counterpart, coloured gas, typically nitrogen, is injected into models to detect leaks and damages. This air-based testing is called pneumatic testing. However, larger amounts of gas can be compressed within the pipe compared to water-based methods, making this system more prone to accidents.

Why is Hydro/Hydrostatic Testing Important in Pipe Production?

Hydrotesting allows manufacturers to stimulate environments, where the pipes produced, are to be used. By testing the pressure expansion and checking the general structural integrity of the model, this testing method helps mitigate the risk of leaks, accidents, or damage that may result from poor production.