Expansion Vessel

A WSE is a legal document that is required on most pressure equipment under the Pressure System Safety Regulations 2000 (PSSR). The WSE lists the components within a system, examinable items and the frequency these should be examined. This is all noted in your WSE.

It is a common misconception that new equipment does not require a WSE, however this is incorrect. All equipment that falls under the regulations must have a WSE in place before it is used for the first time, regardless of age.

Any person deemed competent to create a WSE document can do so if they have the relevant experience and knowledge, however the WSE document must be certified by either an Incorporated or Chartered Engineer, depending on the system size (usually this will require Chartered Engineer qualification sign off).

Under the Pressure Systems Safety Regulations you must have a WSE in place prior to the use of the system. This system will include a rigid vessel and a relevant fluid, mainly gas (carbon dioxide, nitrogen, argon, steam among others), with a pressure at 0.5 bar or above excluding steam, which is at any pressure.

The competent person determines the frequency of examination by item, and notes this in your written scheme. It is most common for the items to be examinable every 12 months.

This is a legal requirement under the Pressure Systems Safety Regulations 2000 (PSSR) and is enforced by the Health and Safety Executive (HSE) and Local Authority. If the regulations are not adhered to, unlimited fines or prosecution from HSE are a possibility.

Equipment capable of operating at 250 bar litres or above, or steam at any pressure, will fall under the regulations. To work this out multiply the maximum working pressure X vessel volume – e.g. 10.0 bar x 50 litre = 500 bar litre.

The WSE is the obligation of the owner so hire units should be covered by the owner of the equipment, unless otherwise agreed.

The written scheme should be completed by an independent body so that impartiality can be proven. This can be completed by a service provider as long as they are competent in this field and impartiality can be evidenced. It is paramount to note however, that the person certifying the WSE must also have the relevant qualifications (e.g. Incorporated or Chartered Engineer).