Written Scheme Examination (WSE)

Under the Pressure Systems Safety Regulations 2000, users and owners of pressure systems are required to demonstrate that they know the safe operating limits of their systems, and that they are safe under those conditions.

Users and owners need to ensure that a suitable written scheme of examination is in place prior to the system being operated. They also need to ensure the system is examined in accordance with the written scheme of examination.

A written scheme of examination is a document containing information about selected items of plant or equipment which form a pressure system, operate under pressure and contain a ‘relevant fluid’.

The term relevant fluid is defined in the Regulations and covers compressed or liquefied gas, including air, at a pressure greater than 0.5 bar (approximately 7 psi) above atmospheric pressure; pressurised hot water above 110 °C; and steam at any pressure.

 The typical contents of a written scheme of examination include:

■ identification of the items of plant or equipment within the system;

■ those parts of the system which are to be examined;

■ the nature of the examination required, including the inspection and testing to be carried out on any protective devices;

■ the preparatory work needed for the item to be examined safely;

■ where appropriate, the nature of any examination needed before the system is first used;

■ the maximum interval between examinations;

■ the critical parts of the system which, if modified or repaired, should be examined by a competent person before the system is used again;

■ the name of the competent person certifying the written scheme of examination; and

■ the date of certification.

A written scheme of examination is required when a compressed air receiver (and associated pipework) where the pressure in Bars is multiplied by the internal capacity in litres of the receiver is equal to or greater than 250 bar litres. 

 Example: 8 Bar compressor with a 50 litre receiver = 8 Bar x 50 litre = 400 Bar Litres this would need a WSE.

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