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Pressure Vessel

The directive lists 13 different modules that define the inspection requirements  of both the manufacturer and notified body.  Two modules, B & B1, cover  design only and have to be used in conjunction with another module covering  manufacture.  Modules H,H1 & G cover both design and manufacture.  The  remaining modules cover manufacture only.  The permitted combinations and usage  of these modules is described below.

Categor y

Normal Route With No QA System

Quality Assurance to ISO 9000  series 

Serial Production

Unit Production

Serial Production

Unit Production


Internal production control


Internal production control with  monitoring of final assessment

D1 Or E1
 D1 (QA To ISO  9002) Or E1 (QA To ISO 9003)
Quality assurance for  production, final inspection and testing


Design examination of type
 Monitoring of final assessment

Design examination 
Product verification

Design examination of type

QA (ISO 9003) for final inspection &  testing

Design examination

 QA ( ISO 9002)
for Production and Test
QA for Design and Production (ISO  9001)


Design examination of type
Product verification

Design examination and Inspection during  manufacture & testing

Design examination of type

QA (ISO 9002)
for final inspection,  testing & manufacture

Full QA with design examination and  monitoring of final assessment.

This is not quite as  complicated as it may appear because all the modules are variations of module A and exist mainly to define the involvement of the Notified  Body.

Module A

  • Prepare Technical  Documentation  covering design, manufacture and  operation.
  • Ensure manufacture conforms with technical documentation
  • CE mark
  • Draw up declaration of conformity
  • Retain all documents for 10 years

The technical documentation should address the essential safety requirements in  section one and two of the directive.  It should include:-

  • Description of the equipment (See section on safety requirements)
    • The purpose of the equipment
    • Operating pressure and temperature
    • Hazard analysis
    • Contents:-  liquid/gas toxic/flammable/reactive corrosive/erosive
    • Flow rates and heat transfer rates if applicable
    • Support structure and imposed loadings such as wind and snow/ice
    • Fatigue / vibration , Varying pressure, thermal cycling, differential  expansion
  • Design and manufacturing drawings
    • Design drawings should contain sufficient information to perform a full  design assessment and supporting calculations.
    • Manufacturing drawings should contain method of manufacture and all relevant  dimensions and tolerances.
  • Instructions to explain the design, operation and maintenance of the  equipment. They should cover:-
    • Intended use
    • Fluid quality and maximum impurity levels if relevant
    • Avoidance of dangers such as contact with hot surfaces.
    • Safety devices required their flow rate and set pressure
    • Maintenance/Inspection requirements
    • Connection requirements
  • Harmonised standards used or justification of the design
    • Material appraisal : list all materials used stating why they are suitable  and that they satisfy the directive.
    •  A list of the ESR's including a  brief statement against the ones that are  relevant stating how they have been  addressed
  • Calculation
    • A full set of calculation should be performed to prove that the design of  the vessel is adequate to withstand the design conditions.
  • Test Reports
    • Material certificates
    • Internal inspection reports covering at least the  hydraulic test
    • NDT reports
    • Quality plans, Procedures covering:- manufacturing, NDT, Welding etc, as  applicable.

If you are making a  pressure vessel and don't know what it will contain or you don't know if the  material being specified to make the vessel is suitable, then you should make  this point clear in the technical documentation.  Ideally you should get a  written statement from the end user stating  that the materials specified are  suitable for the item being manufactured.

Module A1  (Inspection Category 2)
This is the same as module  A except:-

  • Notified body is required to monitor final hydraulic test and examination.
  • Welding procedures and welder approval tests must be witnessed by a notified  body or third  party organization approved under the directive. The standards  used do not have to be EN288 and EN287, they can be any standard considered  appropriate by the Notified Body.

Module B  (Inspection  Category 3 and 4)
This module considers technical documentation only  and has to be used in conjunction with a module covering manufacture such as D,  E F and C1.  It is split into two modules:-

  • B1 Covers the technical documentation for singularly manufactured  units. Any change to the design documentation has to be re-approved by the  Notified Body.
  • B Covers serially manufactured units and permits some variation in  design without requiring re-approval subject to the discretion of the Notified  Body, or as permitted by a harmonized standard.

In addition to  approving the technical documentation the Notified Body has to approve welding  procedures, welders and NDT personnel, or check they have been approved.

Module C1 (Category 3)
This module can only be used in  conjunction with module B, serially produced items, not B1, and there is no C.  Module C1 is basically the same as A1 with the parts covered by B taken out.

Module F (Category 3/4)
This module like C1 must be used  with either B or B1.  If the items are serially produced then this module can be  used in category 4, but if they are manufactured as single items only category  3. it is similar to A1 except the Notified Body must:-

  • Verify qualifications of welding and NDT personnel already approved under module B.
  • Verify material certificates
  • Check safety devices, if applicable.

Module G (Category  4)
This module is for single items only. its the same as B1 and F  except the Notified body performs inspections at various stages of manufacture  as they consider appropriate or as dictated by a harmonized standard. Its the  most popular module being used so far and can be applied to any  category.

QA Modules
If you have an accredited QA system to one of  the ISO 9000 standards then the Notified Body audits your system every 3 years  and pays unexpected visits as it considers appropriate.

  • D1 is the QA version of A1 for category 2.  (ISO 9002.)
  • D is similar to D1 but has to be used in conjunction with either B or  B1. If you are serially manufacturing items you can use this module for category  4, but only category 3 for single items.
  • E requires QA for final inspection and test.  (ISO 9003.)
  • H and H1 are full QA covering both design and manufacture. (ISO 9001.)

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Last Modified 29 August 2001