The Pressure Equipment Directive (PED) requires that individual items of pressure equipment undergo conformity assessment where appropriate. This also applies to assemblies of pressure equipment which need to undergo global conformity assessment (GCA) and CE marking. Experience within the UK indicates that generally this process works well when assemblies are placed on the market as complete, factory supplied products. However when assemblies are created on site at the place of installation the legal process of global conformity assessment is often found to be non-compliant. Assemblies which do not have a global conformity assessment when they are handed over to the end user, may require additional verification to confirm their suitability for service under national legislation such as Pressure Systems Safety Regulations (PSSR). Other than certain Working Party Guidelines published by the European Commission there is no comprehensive guidance to PED currently available to assist the various stakeholders involved in the assembly process. Scope This guidance is aimed at all parties (other than notified bodies or user inspectorates - see note below) who are involved in the design and manufacturer of site installed assemblies in the UK. This includes the following parties: End users (including those responsible for procurement of the assembly or appointment of contractors) Main contractors Site erection contractors Design consultants Control and instrumentation contractors Piping contractors Commissioning teams The document is intended to provide the necessary guidance to all parties with responsibilities for the pressure equipment assembly to ensure global conformity assessment can take place.