Hydrotest: what is a hydrotest and how is it performed?

The gas and petrochemical industries require rigorous industrial controls and inspections to ensure the highest possible level of safety in their facilities. For this purpose, all manner of tests and trials are carried out, the most common being destructive and non-destructive tests.

Destructive and non-destructive testing in the petrochemical and gas industries

What is non-destructive testing?

A non-destructive test (NDT) is a test to detect possible problems on the surface or on the inside of parts.

A non-destructive test, as its name implies, does not require the destruction of the parts, since it is based on the application of physical phenomena such as electromagnetic or sound waves, or other methods that do not involve the destruction of the sample to be tested.

This type of testing has been in existence for decades. Its origins date back to 1868, when magnetic fields were first used to detect surface cracks in railroad wheels and axles.

NDTs are used in various industries: in the automotive, aviation, construction, manufacturing, nuclear engineering and petrochemical (pipeline transport) industries, and others.

They are classified as follows:

  1. Superficial: These provide information on the surface and sub-surface state of the materials. Several tests fall under this heading: VT (visual inspection), PT (liquid penetrant) and MT (magnetic particles).
  2. Volumetric: These reveal the internal condition of the materials. It includes several tests: RT (radiography) and UT (ultrasound).
  3. Tightness: These show the degree to which fluids can be contained in a vessel without escaping to the atmosphere or in any other uncontrolled way. The most common tests used in the oil & gas industry are leak tests and pressure change tests.

What is destructive testing?

Destructive testing of materials is used to verify the physical, chemical and mechanical properties of materials and ensure that they meet the design specifications developed by engineers. Unlike non-destructive testing, these do modify the properties, structure or geometry of the parts being tested, since they serve to simulate the conditions that the samples must withstand in real life.

Destructive tests are performed in all industries whenever it is important to verify the characteristics of the materials. Iron and steel products are always tested in the state in which they will be used.

They can be performed either when the materials are manufactured and/or later in the project to ensure that the material properties have not been altered.

There are several types:

  • Chemical: Verification via procedures such as chemical analysis of components or corrosion tests.
  • Physical: Analysis of physical phenomena such as heat, light or electricity in order to measure variables such as melting and boiling points, the degree of thermal and electrical conductivity or the level of magnetism.
  • Mechanical: Subjection to mechanical forces with a given load.

In this case, it is important that the tests be conducted according to the protocols established in the regulations for each area and material/product.

What is a Hydrotest?

The Hydrotest or Hydrostatic Test is classified as a non-destructive test because the main objective is not to check the resistance, but rather the tightness of the parts.

The hyrdrotest is the most common test for pressure testing of pipes and vessels. It requires that the vessels (pipes, plumbing, gas cylinders, boilers and fuel tanks) or piping system be filled with water or any other liquid that can be stained to visually detect leaks. They are subjected to much more demanding conditions than will be encountered during operation in order to verify that the internal pressure remains constant.

Thus it helps maintain safety and durability standards.

What are hydrostatic tests for?

Hydrostatic testing is used to certify the homogeneity of the products, as it reveals previously undetected material defects.

The 2014/68/EU Pressure Equipment Directive mandates this test on any newly manufactured equipment or piping lines if they are to be installed in the field.

For example, some of the most common objects that undergo this type of testing are fire extinguishers, to ensure that the fire repellent material has not deteriorated or lost efficacy.

At ULMA Forja we perform hydrotests to measure the integrity of flanged junctions in the Oil & Gas and fuel industries, in order to ensure the safety of the facilities and protect the environment, water and nature in general. If a pipeline is designed to operate at a certain pressure, this test must be performed beforehand to know if it is structurally able to withstand the internal pressurerequired.

How is a hydrotest performed?

A Hydrotest or Hydrostatic Test consists of several steps:

  • The test object is placed in a steel chamber simulating a real installation for the test bench.
  • First, the pipe is filled little by little with the precise amount of water needed to fill the line.
  • Air is expelled from the line as it is filled, as it can cause excessive pressure. For this purpose, automatic air release valves or suction cups can be installed.
  • Then the pressure of the pipe, fittings and anchors is checked to ensure it is not over limits.
  • Pressurized water is pumped into the vessel, which will expand forcing the air out of the chamber, releasing the pressure.
  • In case of pressure loss, the test must be repeated until it performs acceptably.
  • The pipeline is emptied carefully, removing the water or liquid in appropriate ways that do not affect the environment.
  • The area is properly cleaned, removing the equipment and tools used.

This test can last up to twelve hours, during which the system must not experience a pressure drop of more than 0.20 bars.

At our in-house facilities at ULMA Advanced Forged Solutions, we perform all types of destructive and non-destructive tests to check the proper condition of our materials. We also perform and report on the hydrotest test for those flanges that are non-standard and designed internally in order to ensure integrity and zero leakage in the flanged junction and validate the design.