In-service Inspection of Pressure Equipment in Europe

and the United States of America - Comparison

Dipl.-Ing. P. Czapek

Introduction

The Pressure Equipment Directive (PED) 97/23/EC lays down uniform technical requirements for pressure equipment in use in Europe. This brings considerable advantages for both manufacturers and operators of pressure equipment:.

Manufacturers can now produce and market their products within Europe without restriction of market access. Operators of pressure equipment can select the manufacturer from a larger pool of potential suppliers throughout Europe.

The API-/ASME/API Codes in the USA are comprehensive technical codes for the design, manufacture and inspection of non-fired pressure equipment. Manufacturers that produce equipment for the US market have to take varying local regulations, based on the ASME Codes, into consideration. The requirements in the USA for the monitoring of manufacture tend to be less stringent, especially in terms of the material qualities and testing, though this is compensated for by more conservative approaches to calculations than in European regulations.

However, the safe and economic operation of pressure equipment in process engineering plant is dependent not only on the characteristic requirements that the equipment and accessories have to satisfy, but in particular on the plant instructions for their operation. The specification of appropriate inspections at suitable intervals is of special importance.

Classification of equipment to be inspected

Most EU states adapted their national regulations governing plant instructions to take into account the changes with regard to the hazard-related classification of pressure equipment that came with the introduction of the PED affecting the placing of pressure equipment on the market. This included, in particular, the classification of test objects for specifying intervals for inspection, together with responsibilities, based on the conformity assessment criteria of the PED. The detailed requirements that operators have to satisfy, in terms of the frequency and intensity of the periodic inspection of pressure equipment within EU countries, is anything but uniform. Since the servicing / downtime costs are major determinants of the economic operation of process engineering plant, it cannot be argued that the starting position in the EU is uniform from a competitive viewpoint.

In most EU countries, the classification of pressure equipment for the specification of inspection intervals is based on the fluid group and the hazard potential (pressure x volume or pressure x nominal width) according to the definitions of the PED. The conformity assessment diagrams and categories of the PED are, however, apparently simplified in most cases and subject to special rules. The conformity assessment criteria have been incorporated in greatest detail into the new German Plant Safety Regulations and in the draft regulations for the Netherlands. The requirements of the PED do not play a role in the classification of equipment to be inspected in the regulations in the United Kingdom, Denmark or Portugal.

Inspection intervals

The statutory inspection intervals in Europe are on average 4 years for internal inspections and 8 years for pressure tests. In some countries these inspection intervals are markedly shorter or longer. For example, the inspection intervals in Austria for vessels with a particularly high hazard potential are 1 year for internal inspections and 2 years for pressure tests, with an option of extending the intervals.

Spain and the Netherlands, in particular, have laid down inspection cycles with longer intervals between inspection for pressure equipment with a low hazard potential - between 4 and 8 years for internal inspections and between 8 and 16 years for pressure tests in Spain. In the Netherlands the first inspection interval after putting into service is between 2 - 6 years - depending on “hazard category” - and after that the interval may be extended under certain conditions up to 6 - 12 years.

Many EU states do not have fixed inspection intervals. In some cases the intervals have to be specified depending on the hazard potential, or the intervals - once they have been specified - may be varied, provided that certain preconditions are met. They are often appreciably extended. Risk assessments and additional investigations (e.g. non-destructive testing) play important roles in the inspection interval specification in these countries. Referring to this some examples:

Although the new Austrian code contains concrete intervals depending on the hazard potential, the user has the possibility to apply an inspection strategy refering to a risk analysis. In this case intervals and scope of inspection are part of the inspection strategy.

In Germany, the statutory inspection intervals for pressure equipment with a high hazard potential are maximum ones. The operator of the pressure equipment assumes responsibility for the actual inspection intervals within the framework of a safety engineering assessment. This also applies to pressure equipment with a low hazard potential. There are, however, no maximum intervals so that the operator can set correspondingly longer inspection intervals.

The Netherlands provides a further example for the flexible setting of inspection intervals. The draft of the new regulations uses inspection plans that are drawn up with the aid of risk assessments as a basis for extension of the statutory inspection intervals. As a general rule, these inspection plans will be reviewed by independent recognized specialists - including those employed by the operator - at the start and regularly thereafter to ensure their continued validity. In addition, if the inspection intervals are extended, then non-destructive testing is required to ensure that there is no major damage to the equipment.

Performance of inspections

Pressure equipment that has a high hazard potential may only be inspected by authorized specialist personnel from inspection bodies (in general with EN 45004 accreditation). Some countries (Germany, France, the UK, Austria, the Netherlands, Belgium) explicitly allow inspection by user inspectorates. The "third-party concept" is not the main approach to periodic inspections in most countries; instead, the focus is on the subject expertise of the inspection body. In Germany, the UK, France and Belgium, pressure equipment with a low hazard potential may be inspected by specialist personnel who do not belong to any authorized inspection body (in general they are employed by the operator).

Comparison with the USA (API Codes)

The periodic inspection of pressure vessels and piping in the chemical and oil-processing industries in the USA is governed by the Pressure Vessel Inspection Code (API 510) and Piping Inspection Code (API 570), issued by the American Petroleum Institute. These codes do not divide pressure vessels into inspection groups. Inspection is a general requirement for pressure vessels. There are exceptions for small-scale equipment with a low hazard potential.

Piping is classified according to the hazard potential of the fluid.

In contrast to most European countries, there are no fixed inspection intervals. Guideline values serve as points of reference for setting inspection intervals (internal inspection every 10 years for pressure vessels, external inspection and wall thickness measurements every 5 / 10 years, depending on the hazard potential, for piping).

The concept of risk-based inspections (RBI) to establish suitable inspection intervals plays a much greater role in the USA than in Europe. The API Codes envisage inspection plans that are drawn up in the course of a RBI and may be verified on a continuous basis through comprehensive non-destructive testing methods. Theoretical considerations, experience of equipment operation, and above all, wall thickness measurements, are used as a basis for the determination of corrosion rates, through which the residual working life can be calculated. This calculated residual life is then used to establish the inspection intervals.

Similarly to Europe, pressure equipment with a high hazard potential may only be inspected by authorized specialist personnel from inspection bodies (with API 510 / 570 accreditation). The API Codes also allow the inspection of pressure equipment by user inspectorates. This is largely favored by the US process industry.

References

[1]      Comments to a request of Working Group Pressure (WGP) concerning in-service
inspections in different EU countries

[2]      National codes for in-service inspections of pressure equipment

[3]      API codes API 510, 570