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.  The application of these components in pressure piping systems under PED jurisdiction is supported by a thorough design validation program, combined with material and product testing to demanding norms and standards. 
 

Pressure piping systems that transport a wide range of dangerous and non-dangerous liquids and gases in European installations must meet the essential safety requirements laid out in the Pressure Equipment Directive (PED 97/23/EC). This soon to be updated legislation 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 (TCF’s), Declarations of Conformity, and application of the “CE” mark.

In relation to mechanical piping systems and their components, this Directive is often largely mis-interpreted 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. The following pages address such topics and outline a best-practices approach to PED-compliance when using mechanical couplings and fittings to join grooved end piping systems. 

Product classification within the PED

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 high pressure filtration (reverse osmosis), concrete pumping, mining slurry systems, compressed air and hydraulic lifting systems - just to name a few.

Product design for a range of piping applications and conditions

Victaulic invests in research and development in order to create innovative products that are robust and well-suited for a broad range of piping system applications for diverse markets and end-users. It is not unusual for the individual product designer to have five or six key markets in mind throughout the product development life cycle. The challenge is often being able to maintain cost-effective designs as the performance criteria evolves from the most basic to the most challenging field applications. 

For example, the planning of a piping system component in a building’s domestic water system is very different from a transportable high-pressure desalination platform. Typically, the operating pressures, temperatures, and loading conditions of the building’s water system do not pose any particular challenges for joint integrity or safety.  

Whereas, the installation of the same product in the desalination system is subject to high stress loads, due to high pressure and possible pressure pulsations, varying temperatures, external bending forces, vibration conditions generated by the pumps and other equipment that must operate continuously, as well as the weight of the pipe itself and the fluid that it is carrying. 

In the second scenario, the total combined loading must be considered during the design stage, if the single product will be used in the full range of systems and multiple market applications. The design and safety review must include all possible scenarios that could be experienced across a multitude of operating conditions. 
 

Structural integrity and materials capable of handling system stresses

When designing products for multiple markets 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. 

Computer-aided design models can easily predict the stress response to input loads in an almost infinite number of locations along the part’s geometry, both internally and externally. 

The data generated from this modelling technique gives the designer valuable insight into how the product will perform under both short term and long term exposure to the loading condition. The designer can easily introduce new material property values (for example, tensile / yield strength, elongation, modulus of elasticity and others) through the modeling program for situations in which these stresses cannot be accommodated by simply smoothing a sharp corner or increasing the material thickness of a particular section. 

During the development of piping system components, it is vitally important to provide a detailed analysis of fluid types that will come in contact with the “wetted surfaces” and adjoining sealing materials. 

This part of the design process involves material technology experts, who are responsible for ensuring long term seal integrity and performance over a wide range of anticipated substances and operating temperatures. They therefore conduct detailed studies to evaluate the seal’s physical properties for any adverse effects of prolonged or cyclical pressure loading, while in contact with these various fluid media. 

This is another area in which Victaulic displays best practices in employing materials development expertise and utilizing techniques and methodologies focused on formulating the most durable and reliable sealing materials available in today’s piping industries.

Safety and hazard analysis

Another process that runs in conjunction with the 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 (i.e. items that are directly exposed to the system operating pressure) are thoroughly analyzed against rigorous criteria outlined in the PED’s Annex 1 (Essential Safety Requirements). 

The information included in a typical Annex 1 file include 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 (e.g.  PED Risk Categories II and III).

Product and material testing

Additionally, at Victaulic and other leading companies, regulatory departments maintain a rigorous product testing program for its line of mechanical couplings and fittings for grooved end pipe. 

Fully assembled products are selected at random on a periodic schedule and are subjected to laboratory testing in accordance with ASTM F-1476and ASTM F-1548. The ASTM standards require that a minimum of five (5) samples be subjected to each test including hydrostatic proof strength, hydrostatic burst, bending moment proof strength, bending moment ultimate strength, axial pull-out (end load restraint) evaluations, pneumatic pressure sealing performance, vibration fatigue and pressure pulsation (cyclical pressure to induce fatigue), among others.

Validation by external Notified Bodies

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

The results of these tests not only demonstrate material consistency and conformity but also serve to validate the material’s ability to be used in pressure system applications in accordance with the PED.  

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, and is held by several global foundry locations. 

In addition, Victaulic is occasionally requested to conduct customized testing for a client who must produce performance data for couplings and fittings for review by their Notified Body (local authority having jurisdiction – AHJ). Such tests are uniquely designed to simulate the specific performance characteristics that will be experienced in the client’s end use application. 

These tests can include various combinations of pressure and bending loads, high and low temperature exposure, high amplitude joint deflection and rotational bending - just to name a few. 

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. 

The Module H Certification not only signifies an important achievement in one’s PED safety program, but also signifies a strong commitment to designing and manufacturing high quality pressure equipment that can be utilized in a wide range of system applications and heavy industries around the world.  

Maintaining global manufacturing consistency

With a global reach in diverse markets, it is essential to not only provide the correct products in a timely manner, but to also ensure consistency in products and materials for the full range of piping system demands in any given region. 

The same techniques described above, to ensure material property compliance to global standards as well as pressure equipment safety for local applications, must be maintained at each production location. Materials are routinely tested to ensure that their physical properties are compliant and consistent with internal manufacturing standards as well as with guidelines that support global compliance with other pressure equipment safety legislation and norms. 

For instance, at Victaulic there is a philosophy to utilize the best independent laboratories, certification agencies, and Notified Bodies, which are world-renowned for the quality and integrity of their surveillance programs. The company relies on these external sources to maintain strict diligence in their reviews and provide input and guidance in order to support efforts in quality and continuous improvement.  

Manufacturing teams interface directly with the various auditing bodies, and it is through this exchange that the specific product safety requirements are made clear and understandable at each production station and in the correct language.   

Remaining diligent in changing markets

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 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 continuously improve safety for the operators and end-users of these components and systems.  The material quality, durability and reliability of Victaulic grooved piping systems and related products have been proven in continuously operating pressure equipment and pressure systems around the world for nearly 100 years. Today, this makes grooved piping system components an easy and obvious choice for PED-compliant projects.