Pressure piping systems that transport liquids and gases in European power installations must meet the safety requirements laid out in the Pressure Equipment Directive. However, this directive is often misinterpreted or misunderstood, writes Len Swantek

 

A typical installation featuring grooved mechanical couplings

Credit: Victaulic

Since their introduction nearly 100 years ago, mechanical grooved piping systems have provided a wide range of performance benefits for system designers, installers and end users in the power sector.

Pressure piping systems that transport a wide range of dangerous and non-dangerous liquids and gases in European power installations must meet the essential safety requirements laid out in the Pressure Equipment Directive (PED 97/23/EC). This legislation will be updated in July and establishes consistent safety practices in pressure equipment and related piping system design, operation and maintenance.

Those who commonly use the directive and its various annexes have come to rely on these guiding principles in the preparation of their conformity assessments, technical construction files, Declarations of Conformity, and application of the ‘CE’ mark.

In relation to mechanical piping systems and their components, this directive is often largely misinterpreted or misunderstood.

For example, many system designers expect that mechanical piping products follow some type of pressure rating protocol based on the system temperature, or that a mechanical coupling is considered pressure equipment. Another misconception is that these types of products require a ‘CE’ mark and must be accompanied by a Declaration of Conformity in order to be considered compliant with the directive.

Product classification

Mechanical couplings and fittings for grooved end piping systems do not meet the definition of pressure equipment or pressure accessories as defined in the PED and other industry-accepted PED guidelines, including the Guidelines Related to the Pressure Equipment Directive 97/23/EC and PD CEN/TR 14549.

By themselves, these material components do not contain a specifically defined pressure boundary and primarily serve to connect two grooved pipe ends, grooved end fittings, or other grooved end components within a pressure system. Therefore, in order to maintain compliance with the directive, these components are not ‘CE’ marked, and they do not require a PED Declaration of Conformity.

Because of some misunderstanding in regard to these requirements, system owners may be mistakenly presented with products bearing the CE mark accompanied with dossier packages containing declarations or conformity statements that are simply not valid for these types of products. This can result in further confusion between notified bodies and their clients as they strive to complete their pressure equipment installation review and related safety inspections in time to meet system commissioning schedules.

However, in contrast, when pressure equipment or a pressure piping system is fully constructed using mechanical couplings and fittings, this entity that functions as a pressure retaining unit does qualify for testing and certification for ‘CE’ marking by the end user under the control of their notified body. This is also a clear requirement for certain risk categories based on the system pressures, temperatures or fluid type and classification.

Some applications here include geothermal systems, turbine cooling water lines, heat exchanger piping compressed air and hydraulic systems, among many others.

The modelling process in product design is a critical step, as potential exposure to static and dynamic loading conditions must be considered

Credit: Victaulic

Product design

When designing products for multiple uses and service conditions, the structural elements and materials of construction are equally important. The modelling process in product design is a critical step, as potential exposure to static and dynamic loading conditions must be considered.

A process that runs in conjunction with design and materials studies is a dedicated and focused review of product safety. Design safety factors are just one part of this review, as the designer also incorporates a comprehensive risk analysis and safety review in accordance with the PED.

In this review, the pressure-bearing components are thoroughly analyzed against rigourous criteria outlined in the PED’s essential safety requirements. The information includes stress calculations, section thicknesses, material properties at ambient temperature with correlation data at elevated temperatures, product performance testing, validation of established ratings and additional correlations between European, US and other international norms. This process alone is very time-consuming, but is viewed as one of the most important in establishing product safety data for critical applications.

Validation

Ongoing physical property testing of the ductile iron casting material is performed by both internal foundry metallurgical labs and external independent testing authorities. These tests include detailed evaluations of tensile strength, yield strength, material elongation, hardness, and Charpy impact resistance.

The data generated from these tests at Victaulic is maintained on file and audited by TÜV Rheinland (Notified Body 0035) as a requirement of its Material Manufacturer QMS Certification of Victaulic’s ductile iron casting material. This certification validates the ductile iron manufacturing process in accordance with PED requirements

In addition, Victaulic conducts customized testing for clients who must have performance data for review by their notified body, which closely simulates the system performance characteristics of the end use application.

The results of these custom evaluations are used by clients and their notified bodies to conduct internal studies on their system designs and are often used by the designer of record in preparing a particular material appraisal (PMA) in accordance with PED Annex I, Section 4.2. For valve products, Victaulic again utilizes the services of TÜV Rheinland for its Module H Certification in accordance with Annex III of the Pressure Equipment Directive.

Remaining diligent

As applicable codes, standards and directives continue to evolve in various industries and markets, manufacturers are challenged to keep up with these changes by applying new compliance systems. The Victaulic Regulatory group remains aware of pending changes in regional piping codes, through direct and dedicated involvement in the codes & standards development process. The goal is to not only stay informed of changes in the codes, but also play a direct role in shaping these requirements through membership and active participation on a wide range of standards committees globally.

Within these groups, the aim is to apply expertise to technical discussions, and also to represent ‘the voice of the customer’ by working toward problem resolutions that will have a positive influence in the relevant markets – and, at the end of the day, to continuously improve safety for the operators and end-users of these components and systems.

Len Swantek is Director of Global Regulatory Compliance at Victaulic.