Hydraulic and pneumatic tests are different

Hydraulic testing uses a liquid; pneumatic testing uses a gas. Under comparable conditions, compressed gas can store much more releasable energy. Choosing air merely because it is convenient can therefore substantially increase the consequences if the assembly or a temporary fitting fails.

A liquid also needs assessment: compatibility with materials and subsequent service, added weight, supports and controlled disposal. Hydraulic testing is not harmless. Decisions must suit the equipment, applicable engineering code and specific purpose of the proposed test.

Define the assembly being tested

The plan should identify boundaries, components, instruments and temporary fittings. Plugs, flanges, connectors and hoses form part of pressure containment; they are not secondary accessories. Their ratings and condition must suit test conditions, rather than only the assembly’s normal operating duty.

Repeated use introduces connection wear and fatigue. Deformed threads, missing identification or questionable repairs need assessment before proceeding. Passing a previous test does not prove that the same arrangement remains suitable after a repair, alteration or component replacement.

Separate people from stored energy

Assessment determines enclosures, protective barriers and exclusion arrangements capable of addressing foreseeable failures. Barrier tape marks a boundary but cannot contain fragments. Locate controls and observation points so that people do not need to stand beside the pressurised assembly.

Leak detection requires a planned method that avoids placing hands or bodies near potential jets. High-pressure fluid injection injury can cause serious injury. Connections must not be tightened under pressure in an attempt to stop a leak while the test continues.

Responsibility and test completion

Competent personnel establish supervision, acceptance criteria and the response to abnormalities. They also define overpressure protection and how safe conditions will be verified before access is allowed. A safe separation distance cannot be chosen merely because it was used on a previous job.

The record should identify exactly which assembly was tested, the method, outcome and any unresolved defects. A satisfactory result does not replace subsequent inspection and maintenance of Pressure equipment during service, or demonstrate that an altered assembly has also been tested.