A Written Scheme of Examination (WSE) is an essential document that is required for pressure equipment to be compliant with the Pressure Systems Safety Regulations 2000 (PSSR).

Whenever a modification is made to any items of plant or equipment related to pressure, an amendment must be made to the WSE in order to remain compliant.

Why should a WSE be amended?

It’s important to amend a WSE to ensure that the documentation you have is up-to-date with regard to the equipment you have in operation. This is crucial in terms of compliance. If a modification took place that was not included in the WSE, you’d be liable under the Health and Safety Offences and Corporate Manslaughter Guidelines should an accident occur.

Without an up-to-date WSE, you’re running the risk of having equipment that is unsafe due to not undergoing the appropriate inspections. This can unfortunately lead to serious and/or fatal accidents, as an issue with pressure equipment can lead to explosions.

As well as creating an unsafe working environment, if the equipment is not modified properly and needs replacing, it can be extremely time-consuming and costly in terms of production should a plant have to shut down. If the Health & Safety Executive (HSE) become involved, it would incur large costs for site visits of c£196 per hour. An example of such an incident is at the Nypro (UK) site in Flixborough.

An amendment would be required if a modification has been made to any items of plant or equipment. This can be as simple as adding or updating vessels or safety items which often occurs due to increased production and the addition of a receiver or compressor to add extra power.


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A WSE covers all protected devices and pressure vessels where a defect might cause danger, so if any modification takes place to an item of this nature, an amendment will need to be made.

All WSEs need to be reviewed periodically and, during the inspection, the engineer will check that your equipment aligns with what is listed in the WSE. The frequency of examination does differ depending on the body who is undertaking the inspection. Generally speaking, working examinations - which involve non-intrusive pressure testing - will take place annually. Thorough examinations - which would involve isolating and opening up the vessel - often take place bi-annually, or every three years. For stainless steel equipment, this can be extended to five years.

To find out more information about how often a WSE should take place, download our guide ‘The Essential Questions to ask your Engineering Inspection Supplier

What is included in a WSE?

According to the INDG178 Written Schemes of Examination guidelines, “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’”.

While the contents of a WSE will vary, typically, a WSE will 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 WSE
  • The date of certification.

As there is no standardised WSE, not all of them will contain the same information, some will be more comprehensive than others. For more information on what to expect from a WSE, read our blog on how much a WSE costs.

Whose responsibility is it to amend a WSE?

Only a competent person may amend the scheme and it is the responsibility of the duty holder/owner to choose which competent person carries out this task.

This decision should be made depending on the complexity of the equipment. As mentioned in SAFed’s Contents of PSSR Written Schemes of Examination guidelines, pressure systems are divided into three categories (minor, intermediate or major) depending on the complexity of the equipment. While there are no clear dividing lines between these categories, they are in place to indicate the attributes and competencies required of the competent person undertaking the examination.

A major system, for example, requires specific, specialist experience, which not all engineering inspectors will have. It is the duty holder’s responsibility to ensure the competent person they appoint has the relevant credentials, skills and expertise to undertake the examination to the standards required for a WSE.

Until the WSE is amended, the equipment in question cannot be operated. If a duty holder decides to continue to use the equipment, they are then legally liable and could be prosecuted should an incident occur, or they are audited by the HSE.

While shutting down equipment can be costly in terms of production loss, continuing to operate without a valid WSE can be even more damaging should the HSE become involved, or if litigation were to take place due to a serious accident. Both scenarios demonstrate the importance of ensuring WSEs are kept up to date and amendments are made as soon as a change to the equipment has been undertaken.

To make sure that you are completely ready your your inspection, download our completely free checklist on how to prepare for your PSSR inspections

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