Hydrostatic Testing

Last update: Jan 13, 2017

Hydrostatic (Hydro) Testing is a process where components, such as piping or pressure vessels are tested for strength and leaks by filling the equipment with pressurized liquid. For pipelines, hydro tests are conducted while the pipeline is out of service. All oil and/or natural gas is typically vented off, and the line is mechanically cleaned prior to testing.

Hydrostatic testing works by completely filling the component with liquid (usually, but not always, water), until a specific pressure is reached. The hydro test pressure often exceeds the designed working pressure of the equipment, sometimes by over 150%, depending on the exact regulations and code requirements, as applicable. The pressure is then held for a specific amount of time to inspect visually for leaks. The visual inspection can be enhanced by applying either tracer or fluorescent dyes to the liquid, as required or needed.

Hydrostatic testing is often required as a final proof test after repairs are completed and equipment is returned to service. While it can tell you whether or not leaks are present, a hydrostatic test does not necessarily ensure the integrity of the component beyond the time period of the actual test. On-going equipment integrity is best managed by an effective, integrated fixed equipment mechanical integrity (FEMI) program.

There are two additional methods of hydrostatic testing: water jacket testing and the direct expansion method. These are more often used for cylinders or vessels.

  • With water jacket testing, the vessel to be examined is filled with water, after which it is placed in a sealed container which is itself filled with water and connected to a calibrated gas tube. It is at this point that the vessel is pressurized for a period of time before being subsequently depressurized. Pressurizing the vessel forces water out of the test jacket and into the tube. Operators can then determine how much the vessel expanded. This method does cause some slight, yet permanent stretching to the vessel.
  • With the direct expansion method, the vessel being examined is completely filled with water. Then additional water is pumped in until it reaches the test pressure. The amount and weight of the water forced into the vessel, along with the amount not expelled from the vessel upon the release of the pressure allows the inspector to determine how much the vessel expanded.

Hydrostatic testing can be used to examine many different types of equipment, including pipelines, fire extinguishers, storage tanks, and gas cylinders. It is particularly useful for pipelines in situations where the use of inline inspection tools are not feasible.

Prior to conducting a hydrostatic test, one should consider the specific gravity and chemistry of the hydro test fluid both in terms of loads and corrosivity (e.g., chloride content of water), and how this may impact the equipment. For example, some equipment foundations and piping supports may not be designed to handle the loads. When hydrostatic loads are unacceptable, alternative test methods should be considered such as pneumatic testing or other gas leak testing. When using gasses (e.g., air or nitrogen), special caution should be paid to safety as gas pressurization results in significantly higher amounts of stored energy in the test subjects, which can result in catastrophic failures. It is best to use a customized procedure, created by competent personnel, for this type of testing.


Recommend changes or revisions to this definition.


Join 8,000+ fellow asset integrity professionals! Get Inspectioneering's latest information straight to your inbox. Enter your information below:

January/February 2015 Inspectioneering Journal
By Serge Bisson at GCM Consultants, and Hugo Julien, P.E. at GCM Consultants

Are you still hitting the welded joints of pressure vessels with a hammer during hydrostatic testing? If yes, then you’re due for a refresher on the pressure testing requirements of ASME Section VIII Division 1 since this requirement was for pressure vessels back in the mid 1940’s. This article will help you by highlighting the main requirements of, and differences between, the hydrostatic test for new pressure vessels fabricated according to ASME Section VIII, Division 1 and the hydrostatic leak test for new piping systems made under ASME B31.3.

New Inline Inspection Technology Helps Ensure Terminal & Pipeline Integrity Management Success
March/April 2014 Inspectioneering Journal
By Ron Maurier at Quest Integrity Group, LLC, and Dan Revelle, Sr. at Quest Integrity Group, LLC

New inline inspections and integrity management systems allow operators to understand the complexities and economics of terminals’ and station’s complex aging pipeline infrastructure.

Real-time Operating Decisions Made Easier
January/February 2013 Inspectioneering Journal
By Devon Brendecke, P.E. at Quest Integrity Group

The benefits of adding fitness-for-service (FFS) assessments to energy sector reliability projects are numerous. The acceptance of API 579/ASME FFS-1 is increasing across the energy sector and other industries, as these benefits have been demonstrated in a wide range of projects. Several of these benefits are illustrated in this article using real-world examples.

Have you determined whether or not your equipment is subject to Brittle Fracture?
Partner Content

Auto-refrigeration can impose low temperatures onto process vessels and piping causing them to be at risk of brittle fracture, the sudden break-before leak phenomena that can result in catastrophic rupture of the equipment.

January/February 2012 Inspectioneering Journal
By Devon Brendecke, P.E. at Quest Integrity Group

Thanks to constantly improving technology developments, inspection of atmospheric storage tanks has yielded better data which, when used as input, improves the accuracy of advanced assessment techniques. Coupling the improved inspection data with an advanced engineering assessment often means that tank operators are able to postpone repairs until the next shutdown, eliminate the need for repairs or be exempt from hydrostatic testing.