"Large parts of this procedure are not applicable anymore due to the recent European regulations such as PED"

Table of Contents

  1. Purpose
  2. General
  3. Responsibilities
  4. Guidelines
  5. Preparation of the Guide for Projects
  6. References

1. Purpose

The purpose of this guideline is to describe the way in which the "nader onderzoek" (final examination after installation) will be executed by Stoomwezen BV and which activities are required from the various Company Departments.

2. General

2.1 Terminology

The "Rules for Pressure Vessels" use the term 'pressure apparatuses' for equipment and systems under pressure, thus including vessels, reactors, heat exchangers, boilers, piping systems etc. The Rules are, in principle, made for Steam Act pressure apparatuses, but are also applied to Non-Steam Act pressure apparatuses (in the Nether­lands generally known as "druktoestellen").

2.2 Justification of the "Nader Onderzoek" (Steam Act Pressure Vessels)

In accordance with the Steam Decree, section 12, subsection 5, (ref. 6.3) the examination of a steam or vapor apparatus also comprises a final examination, being an examination with regard to the set-up (or instal­lation), lay-out and appurtenances of the apparatus.

The purpose of the examination is to satisfy Stoomwezen BV, that the plant or applicable part of it is safe and protected as intended by the Steam Decree. The detailed content of the examination is described in section 4 of this guideline.

2.3 Non-Steam Act Pressure Apparatuses

Non-Steam Act pressure apparatuses require only a "nader onderzoek" if the permit grant for the operating license of the subject facilities (based on the Environmental Management Act) contains a condition that such apparatuses have to be inspected by the "Dienst voor het Stoomwezen" or an organization accepted by the latter. For the purpose of this guide this accepted organization can be assumed to be Stoomwezen BV.

The formulation of this condition and its interpretation may vary from one permit grant to another.

2.4 Fulfillment of the Requirements of the Steam Decree

The Steam Decree (ref. 6.3) contains a large number of provisions regarding the appurtenances of steam and vapor vessels, which are elaborated, explained and supplemented in the "Rules for Pressure Vessels". With the exception of the provisions regarding:

  1. safety valves, rupture disks and other appurtenances which serve to prevent that the allowable operating conditions will be exceeded, such as pressure, temperature and flow switches for cut out systems, and

  2. appurtenances such as remotely operated level gauges on boilers,

these provisions are not verified by Stoomwezen BV on a preventive basis.

For documentation requirements see 4.2.4.

3. Responsibilities

The Authority Engineering Group, a member of which acts as Stoomwezen Coordinator (ref. 6.5 and 6.8), or the Representative/Deputy of the Stoomwezen Coordinator at site, has the prime responsibility for all coordination with Stoomwezen BV and guiding the activities to be performed by other Company Departments in relation to this guideline.

The Company Construction Department has the prime responsibility for the compila­tion of all field documents required and/or applicable for the "nader onderzoek" and for supporting the necessary activities in the field.

Other Company Departments involved in the "nader onderzoek" or aspects thereof may include, e.g., the Procurement Department (particularly the Inspection Group), the Engineering Department and the Process Department.

4. Guidelines

4.1 Timing, Request, Results and Duration

4.1.1 Timing of Execution

The "nader onderzoek" should be executed when the steam and vapor vessels have been erected (practically) "ready for operation", i.e. when the equipment items and the related other equipment inclusive of pip­ing, control systems etc. are mechanically complete.

On larger projects, the "nader onderzoek" activities will normally be spread over a prolonged period, particularly for piping systems since these become ready over a longer period; combination with inspection work by a Stoomwezen inspector is recommended.

4.1.2 Request for "Nader Onderzoek"

The request for a "nader onderzoek" should be made in writing or by facsimile by the Stoomwezen Coordinator or by his representative/deputy at site. The request should be sent to the responsible Stoomwezen BV regional office for the attention of the agenda officer, at the latest about three (3) weeks in advance of the expected mechanical completion of the plant, unit or applicable part of it.

Before issuing the request it is advisable to check the following with the responsible Stoomwezen office :

  • how many equipment items are administratively ready for the ‘nader onderzoek’;


This information is usually available with the Coordinator as part of the document assessment activities.

  • which instrument testing is to be witnessed by Stoomwezen BV as part of the ‘nader onderzoek’ (for example : low level trips of boilers, temperature trips of furnaces, both simulated and actual)

  • Note:

  • In such cases, the instrumentation supervisor has to include such activities in his testing schedule in order to invite the Stoomwezen inspector.

Timing and extent of the "nader onderzoek" should be carefully coordinated with the Stoomwezen BV regional office because they need also some office time for preparatory activities. If done so, the examination will be effective and can take place as scheduled. See also 4.2.2.

4.1.3 Time Consumption of the "Nader Onderzoek"

Based on former experience, the "nader onderzoek" should be scheduled for approximately the following typical duration’s:

  • for a crude distillation unit 3 days

  • for a hydrotreater unit 1 day

  • for a distillate fractionation unit 2 days

  • for an amine unit 1½ days

  • for a utility distribution system 1½ days.

The duration for other types of units should be estimated in proportion with the above examples, noting that for practical reasons the duration should not be defined in periods shorter than ½ day.

If also a "nader onderzoek" for non-Steam Act pressure vessels ("drukvaten") is re­quired, the duration can be estimated by multiplying the above figures with the ratio :

Steam vessels+vapor vessels+"drukvaten"steam vessels+vapor vessels

4.1.4 Result of the "Nader Onderzoek"

A successful completion of the "nader onderzoek" will result in the issue of a start-up permission to the client for the plant, the unit or part of it. Initially, such permission will have the format of a signed-off/stamped checklist or a simple written and signed/stamped document per item or system checked. The formal documents (CEOC-certificates, licenses and declarations of no objection) normally follow at a later date.

Pressure vessels and piping systems subject to licensing on basis of the Steam Act will receive a license. Pressure vessels subject to Stoomwezen inspection and acceptance on basis of the conditions of the environmental permit receive a declaration of no objection (“VGB”). All other pressure vessels inspected by Stoomwezen BV receive a declaration of manufacturing and first test (“VVB”).

4.2 Details of the Execution of the "Nader Onderzoek"

4.2.1 Systems Subject to a "Nader Onderzoek"

Systems subject to a "nader onderzoek" are all plants, parts of plants, plant systems and units, containing steam or vapor boilers and/or vessels, and/or piping systems subject to Stoomwezen approval.

For Non-Steam Act pressure vessels, which may include piping systems, the requirement for Stoomwezen approval exists only if the condition stated under 2.3 is fulfilled. The extent of the "nader onderzoek" then depends on the formulation of the condition of the permit grant.

No principle difference has been made between steam and vapor vessels and Non-Steam Act pressure vessels in 4.2.2 and further.

4.2.2 Appointment with Stoomwezen

The Company Construction Department, represented by the Coordina­tor's Representative/Deputy at site, should arrange for the appointment(s) with Stoomwezen BV to execute a "nader onderzoek".

For large(r) projects, the amount of work connected with the "nader onderzoek" -- including the office work which precedes the field activities -- is often sufficient to warrant formal scheduling by the Construction Department and prior discussion of the organization and the scheduling of the work with Stoomwezen BV (see 4.1.2).

4.2.3 Verification Activities by the Construction Department

Before the "nader onderzoek" can be started, the Coordinator's Representative/Deputy at site should verify or arrange for verification of the items listed below.

Nameplates and identification marks

Verify that the Stoomwezen nameplates and/or identification marks on all steam and vapor boilers and steam and vapor vessels are in accordance with the Stoomwezen rule on identification marks (ref. 6.6) and with the latest issue of the clas­sification list(s) (ref. 6.2). If the "nader onderzoek" comprises also Non-Steam Act pressure vessels, then the same is applicable for all Stoomwezen name­plates on these vessels. Differences such as errors, missing data etc. should be reported to the Stoomwezen Coordinator to enable finalization of the classification list(s).

Verify that these Stoomwezen nameplates have been stamped on all four rivets or on all tack welds between equipment and nameplate with either the Stoomwezen symbol (lion) or with the corresponding symbol of the non-Dutch third party organization.


  1. Piping systems and very small vessels (volume equal to or less than 0.01 m3 normally do not have a name­plate; for these cases, the Stoom­wezen symbol is stamped near the registration number, usually in front of or at the end of this number, or both.

  2. Equipment that has been fabricated outside the Netherlands and that has been inspected by a local Third Party organization under the terms of EEC guideline 76/767/EEG (ref. 6.7), should have been stamped with the symbol of this Third Party Organization, who should be a member of the CEOC organization (see Attachment 3 of ref. 6.4).

Piping materials and systems

Verify that all piping materials and piping systems have been treated as described in the Guide for Coordination with Stoomwezen BV (ref. 6.8).

This implies in particular verifying that :

  • marking and remarking of 'Stoomwezen' piping and fittings (with, e.g., heat number, factory mark, third party inspector stamp) have been carried out properly by the piping material manufacturers and the piping construction subcontractor;
  • material certificates required by the "Rules for Pressure Vessels" and/or the Stoomwezen BV approval letters ("Nieuwbouwrapporten") for pip­ing systems are available for the Stoomwezen BV inspector;
  • all welding has been executed in accordance with the "Rules for Pressure Vessels" and/or the Stoomwezen BV approval letters for piping systems (properly qualified welders, welding procedures accepted by Stoomwezen BV, or, if fabricated outside the Netherlands, by an accepted local Third Party Organization etc.);
  • test results such as radiographic films (with location plans), ultrasonic, magnetic particle and dye penetrant reports and hydrostatic test reports are available for the Stoomwezen BV inspector;
  • reports on special treatments such as heat treatment are available for the Stoomwezen BV inspector;
  • Stoomwezen BV register and -- if issued -- sequence numbers and the stamp of the Stoomwezen BV inspector who inspected the pipe spools before installation have been properly marked on the piping systems.


  1. Sometimes the register number will be placed on a weld-on plate.

  2. Some piping shops have received a delegacy from Stoomwezen BV for pipe spool marking; in such cases, the stamp shall be placed by the assigned person of the piping shop.

  3. For piping spools or systems fabricated outside the Netherlands, an inspector of a local Third Party Organization -- being member of the CEOC organization -- will often provide the stamping.

all information on the tag plates of safety valves matches with the safety valve certificates, referencing the safety valve item numbers on the classification list.

blow off lines of safety valves have open ends and that no obstructions (valves etc.) are located in these ends.

all relevant forms are legible, complete, signed and stamped by the manufacturer and/or piping construction subcontractor;

the latest issues of engineering documents such as engin­eering and utility flow diagrams, line designation tables and, for piping systems subject to formal stress assessment, the overall piping system drawing(s) is (are) available (see 4.2.4, B).


  1. It is recommended to prepare a centralized file of all documentation for this "nader onderzoek" and to ensure that the various documents can be easily related to each other by, e.g., using the heat numbers; this promotes the information retrieval and saves time during this last phase of the construction work. When agreed so with the Stoomwezen BV Inspector, he should be provided with storage facilities which are only accessible to himself.

  2. To facilitate the checking of certificates by the Stoomwezen Inspector, a compilation should be made for each category of certificates, containing information such as size of the piping components involved, the heat number and the charge number. A number of columns should be included for use by the Inspector.

  3. By acting in this way, the field inspection by Stoomwezen BV can, for piping systems, be limited to field welds, hydrostatic testing (if not yet done), register number checking, pipe supports checking on type, location and sometimes, operability and late changes to (parts of) the piping systems, if any.

  4. For large(r) projects, a considerable portion of the 'paper work' should be (and is) done beforehand by Stoomwezen BV in order to reduce the field effort for the "nader onderzoek", i.e. during the piping (pre)fabrication and erection activities. The centralized file addressed under note 1 above will be a good tool for this work.

It is recommended that the verification activities will be performed, to the extent reasonably possible, at the receipt of equipment and materials, or otherwise during the installation activities.

4.2.4 Compilation of Documents

Before the "nader onderzoek" starts, the following documents should be compiled:

A. by the Authority Engineering Group (for submittal to Stoomwezen BV):

  • (copies or originals of) Test and Measuring Certificates ("meetbrieven") of safety valves and rupture discs in the plant, part of plant or system;

  • (copies of) test curves of pumps, compressors and blowers;

  • Note:To be submitted by manufacturer through the Company Inspection department.

  • further information and data as requested by Stoomwezen BV during the main procedure, for example information on alarm settings live tests, details on locking systems etc.

The desired documents and information should have been specified by Stoomwezen BV during the main procedure. The main procedure documents such as classification lists, line designation tables and engineering flow diagrams will have been submitted to Stoomwezen BV up to and including their latest issues as part of the main procedure (ref. 6.10).

Additionally, the following documents shall be submitted:

  • the original CEOC-certificates as prepared by the local Third Party Organizations for equipment fabricated outside the Netherlands
  • the manufacturing data books as prepared by the foreign manufacturers for equipment fabricated outside the Netherlands.


  1. These documents should, according to the Rules, be submitted by the manufacturers or the local Third Party organizations involved; since this does not always happen, follow up by the Inspection and/or the Authority Engineering group is necessary.

  2. A verification by Company of both sets of documents to ensure that both show the same and the correct data is recommended to avoid delays and extra work due to non-acceptance by Stoomwezen BV.

B. by the Company Construction Department (to be available for the Stoomwezen Field Inspector:

  • (copies of) the Test and Measuring Certificates( “Meetbrieven”) of the relevant safety valves and rupture discs in the plant, part of plant or system;

  • (copies of) test curves of pumps, compressors and blowers;

  • all relevant engineering and utility flow diagrams;

  • copies of the classification list, the line designation tables (see 4.2.3, under “Piping Materials and Systems”) and any other documents as indicated by the Stoomwezen Coordinator.

4.2.5 Assistance to Stoomwezen BV

During the "nader onderzoek", the Coordinator's Representative/Deputy at site should be available or arrange for the availability of an engineer to assist Stoomwezen BV and/or to be present with the examinations.

4.2.6 Stoomwezen BV Activities

During the "nader onderzoek", Stoomwezen BV will execute the follow­ing activities.

A. Office activities:

  • check of all engineering and utility flow diagrams for the safety protection of equipment;

  • check of all test curves of pumps, compressors and blowers as specified by themselves;

  • check of test and measuring certificates of safety valves and rupture discs, as specified by themselves;


Safety valve certificates comply with Stoomwezen requirements if they contain information on (1) the height of the government ring (2) the spring diameter, the spring wire thickness, the unloaded spring length and the number of windings.

  • verification of the further information and data as requested by themselves during the main procedure (see 4.2.4);

  • verification of the original CEOC-certificates received from the Authority Engineering Group, from the manufacturers or from the local Third Party Organizations for equipment fabricated outside the Netherlands, against the manufacturing data books and the classification lists; these documents will be kept by Stoomwezen BV for the preparation of licenses and declarations of no objection

  • verification of the manufacturing data books received from the Authority Engineering Group, from the manufacturers or from the local Third Party Organizations, for compliance with the inspection requirements contained in the approval letters of the equipment fabricated outside the Netherlands; these documents will be returned by Stoomwezen BV after review and acceptance.

This document checking will, whenever possible, be done in the Stoomwezen BV office in order to minimize their field activities, particularly on smaller projects where no Stoomwezen BV inspector will be permanently assigned to the project.

The results of the checking and verification activities is laid down in a so-called 'Nader onderzoek rapport' for the individual equipment items and piping systems subject to a license, a declaration of no-objection or inspected and tested on specific Company/Client request.


Equipment items and systems NOT subject to a license or a declaration of non-objection are normally not checked by Stoomwezen BV.

B. Activities for equipment constructed at site:

For equipment items that are constructed or erected at site, either entirely or from pre-assembled parts, some Stoomwezen related activities are required at site; typical examples include large storage vessels including spheres and large furnaces, boilers and heaters.

Such activities include (without necessarily being complete):

  • contacts with Stoomwezen BV for fabrication inspection, final inspection and acceptance at site

  • definition of hold points with and for Stoomwezen BV inspection (e.g., fit ups)

  • document review by Stoomwezen BV

  • definition of hold points with and for Stoomwezen BV inspection (e.g., fit ups)

  • document review by Stoomwezen BV

  • hydrotest in the presence of Stoomwezen BV

  • the "nader onderzoek" by Stoomwezen BV when all piping has been connected and all appurtenances have been installed

  • stamping of nameplate by Stoomwezen BV at successful completion of the "nader onderzoek".

These activities are normally included with the subcontract for construction/erection.

The Coordinator's Representative/Deputy has only a supervisory role for these activities.

C. Field activities:

  • visual field check of the plant or units as installed against the engineering and utility flow diagrams;

  • field check of all steam and vapor boilers and vessels for registration number and Stoomwezen BV or CEOC member symbol on the nameplates; in case also "drukvaten" have to be inspected the same applies to these vessels;

  • presence with hydrotests of piping systems if done at site;

  • field check of safety valves, including interlock systems etc., as installed;

  • presence during the blow-off of boiler safety valves;

  • check on the proper functioning of automatic starting devices for spare pumps, the cut-out systems for, e.g., furnaces and reboilers and/or other essential safety systems;

  • any further check on safety systems as required by themselves; such further checks will normally have been specified during the main procedure for the project (see ref. 6.9/6.10).

4.2.7 Follow-up on Stoomwezen BV Activities

Any notes or remarks made and/or any corrective actions specified by Stoomwezen BV during the "nader onderzoek" should be resolved or executed on a mutually agreed basis. This includes corrections of administrative nature such as removal of errors in CEOC-documents.

Stoomwezen BV may, at their option, issue a conditional start-up permission or hold this permission until the outstanding points have been cleared.


The so-called 'hold points' are often related to essential safety items; the emphasis is laid on equipment items and systems subject to a license or a declaration of non-objection, since non-compliance’s with these items or systems may have juridical consequences for Stoomwezen BV.

5. Preparation of the Guide for Projects

Because each project is different again the above guidelines should be reviewed when they will be used for a project. For smaller projects some simplifications may be possible, for other projects additional agreements with Stoomwezen BV may be useful.

If it is decided to modify the guidelines for a specific project, a separate document should be issued for this project.

In turn, specific experiences from a project may lead to an update or modification of these guidelines.

6. References

Document Number
6.1 BN-EG-UE203 Defining Information to be Submitted to Pressure Vessel Authorities 5
6.2 BN-EG-UE214 Preparation of Equipment Classification Lists for the Dutch Pressure Vessel Authorities 5
6.3 G-0203 Steam Decree (1953, with updates) as contained in the "Rules for Pressure Vessels" -
6.4 G-0301 Stoomwezen Rule, "General Procedure" -
6.5 G-0401 Stoomwezen Rule, "Procedures for Pressure Vessels in Installations" -
6.6 G-0601 Stoomwezen Rule, "Identification Marks" -
6.7 76/767/EEC Guideline Regarding the Acceptance of Inspections Executed by Local Inspection Organizations -
6.8 BN-EG-UE... (later) Guide for Coordination with Stoomwezen BV 5
6.9 BN-EG-UE217 (later) Guide Regarding Procedural Information Stoomwezen BV 5
6.10 BN-EG-UE218 (later) Guide for Information to be Submitted to Stoomwezen BV 5


References 6.9/6.10 are available as Attachments 1 and 2 of Ref. 6.1, Defining Information to be Submitted to Pressure Vessel Authorities (BN-EG-UE203).