This article discusses need for introducing new standards for developing efficient piping systems. A barrier to wider adoption of the material has been the absence of non-metallic piping standards that could serve as a common language for manufacturers, fabricators, designers, and other stakeholders. The development of the new standards also reflects the growing international role of ASME standards. The intent of ASME NM-1 is to set engineering requirements for safe design and construction of thermoplastic piping installations. The ASMI NM-2 is expected to address pipe and piping components which are produced as standard products, as well as custom products designed for specific applications. The ASME NM-3 Standard intends to provide greater uniformity, consistency, and transparency for the identification and establishment of physical properties and allowable stress values for materials in non-metallic piping systems. The standards for thermoplastic and fiberglass reinforced plastic piping systems are being developed to fill the unmet need for comprehensive documents in these areas.
It is no surprise that non-metallic piping is gaining favor for handling fluids in process plants and pipelines. Non-metallic piping generally weighs less and is potentially less costly than comparable metallic piping. What's more, most non-metallic materials resist corrosion that can shorten the life of metals.
A barrier to wider adoption of the material has been the absence of non-metallic piping standards that could serve as a common language for manufacturers, fabricators, designers, and other stakeholders. While various standards have begun to address the use of non-metallic materials in industrial piping, they do not provide adequate requirements to cover the service limitations, design, materials, fabrication, installation, fusing or joining, and quality control of non-metallic piping systems.
Beginning a century ago with the Boiler and Pressure Vessel Code, these are the issues in which ASME has excelled as a standards development organization. That's why ASME has turned its attention to non-metallic piping and expects to publish its first set of standards covering the subject in late 2016 or early 2017.
Standards for non-metallic piping systems are significantly different from those applicable to piping made of steel and other metals, and the development of rules for non-metallic materials requires a unique set of expertise. Accordingly, ASME assembled the Committee on Non-metallic Pressure Piping Systems (NPPS) in 2011 for the purpose of formulating standard rules for the construction of non-metallic pressure piping systems.
The committee and its subordinate groups are composed of stakeholders from different industries with expertise in dealing with a wide range of non-metallic materials. As with most ASME standards committees, members represent widely differing perspectives. They include designers, manufacturers, operators, insurers, and regulators.
The standards under the scope of the committee will cover the design, manufacture, fabrication, installation, examination, testing, and inspection of thermoplastic and glass-fiber-reinforced thermosetting resin piping systems suitable for pressure applications. They will also cover specifications for non-metallic materials (other than wood, glass, and concrete) for pressure applications including material design values and limits on the use of non-metallic materials.
Currently, designers, fabricators, installers, owners, and others in the industry develop a wide variation of customized designs among the suppliers of these products. The standards developed under the NPPS Standards Committee will provide uniform quality control of materials and dimensions of the associated piping components and will enhance safety by promoting interchangeability and reliability of systems.
The NPPS Committee is currently developing three standards: ASME NM-1 Standard on Thermoplastic Piping, ASME NM-2 Standard on Glass Fiber Reinforced Thermosetting Resin Piping, and ASME NM-3 Standard on Non-metallic Materials.
The intent of ASME NM-1 is to set engineering requirements for safe design and construction of thermoplastic piping installations. It covers pipe, flanges, bolting, gaskets, valves, fittings, special connecting components, and the pressure-containing portions of other piping components. It will also include hangers and supports and other equipment items necessary to prevent overstressing the pressure-containing components.
The temperature limits for each thermoplastic material will contain a maximum continuous-operating temperature and pressure and a maximum short-term operating temperature and pressure for a given time.
Engineering requirements of this standard, while considered necessary and adequate for safe design, generally use a simplified approach. A designer may choose to apply a more rigorous analysis, but the approach must be documented and accepted by the owner.
At present, engineering companies designing this equipment for electric power generating plants have difficulty justifying their designs using existing standards. ASME B31.1 and ASME B31.3 limit the pressure in thermoplastic piping systems to 150 psi at 140 ̊F. However, there are applications for thermoplastic piping systems above 150 psi at a wide range of temperatures. The NM-1 Standard will provide realistic temperature and pressure ranges for using thermoplastic piping systems.
ASME NM-2 will provide requirements for the design, materials, manufacture, fabrication, installation, examination, and testing of glass-fiber-reinforced thermosetting resin piping systems. In industrial use, this type of piping is commonly referred to as FRP piping. The abbreviation stands for “fiberglass reinforced plastic.”
“There are a number of FRP product standards available in the industry that provide procedures for designing products for pressure containment,” said Bruce Hebb, vice president of engineering at RPS Composites in Mahone Bay, Nova Scotia, and a member of the NM-2 Subcommittee, “but there is very little direction on how to properly analyze FRP piping systems. The most common type of FRP pipe, i.e. pipe that is filament wound at 55 degrees to the pipe axis, displays significantly different axial strengths depending on whether the stress is due to pressure or due to other loads, such as bending due to weight loading. Proper analysis of the piping must recognize that behavior so as to achieve a consistent margin of safety under various loading conditions.
“It is also necessary to recognize that FRP is not a ductile material: it does not shake down to elastic behavior,” Hebb said. “So it is not appropriate to deal with displacement-induced loadings in the same way as is done for ductile materials. The new ASME FRP pipe standard will address these very important issues. Adherence to the requirements of the Standard will provide greater confidence in the safety of FRP piping, and greater reliability of FRP piping systems.”
Like the ASME NM-1 Standard, NM-2 will address pipe and piping components which are produced as standard products, as well as custom products designed for specific applications. This standard also includes hangers and supports and other equipment necessary to prevent overstressing the pressure-containing components. In addition, the ASME NM-2 standard will cover piping and piping components manufactured by contact molding, centrifugal casting, filament winding, and other methods.
Present rules for FRP Piping are found in ASME B31, RTP-1, and BPV Codes in which they only address rules for reinforced thermoset plastic corrosion-resistant equipment, and none specifically for pipe and piping components or other non-metallic product forms. The Boiler and Pressure Vessel Code Section III has a few Code Cases that address rules for selected non-metallic piping and components including fiberglass reinforced plastic and selected thermoplastics such as high density polyethylene and polyvinyl chloride. However, in some of these cases, this represented old methodology.
Similar to the function that Section II of the Boiler and Pressure Vessel Code serves for metallic materials, ASME NM-3 will provide a repository for allowable stress values and physical properties of non-metallic materials. Initially NM-3 will specifically support the NM-1 and NM-2 construction standards, but the long-term vision for NM-3 is to support ASME construction codes including the Boiler and Pressure Vessel Code, B31 Pressure Piping, B16 Valves, Flanges, Fittings, and Gaskets, and Reinforced Thermoset Plastic Corrosion Resistant Equipment.
At present, the design of non-metallic piping systems requires the designer to rely heavily on manufacturer-specific material properties and suggested allowable stress values. As a result, a complete set of required properties is not always readily available and suggested values can vary significantly between manufacturers. Additionally, the bases of and inherent margins in the allowable stress values are not always well defined. Collectively, these differences can result in wide variations from one system to another in overall design margin.
ASME NM-3 will provide a complete set of required physical properties and allowable stress values for many non-metallic materials in a consistent format, along with clearly defined bases for these properties and values. The NM-3 standard will also include numerous non-metallic material specifications for this initial set of materials and will lay out a robust process for including additional non-metallic materials in future editions. The NM-3 Standard intends to provide greater uniformity, consistency, and transparency for the identification and establishment of physical properties and allowable stress values for materials in non-metallic piping systems.
“ASME codes and standards have become the gold standard for the design and construction of metallic pressure vessels and piping systems throughout North America and around the world,” said Thomas Musto of Sargent & Lundy LLC in Chicago. Musto serves as chairman of the NM-3 Subcommittee. “The ASME Non-metallic Pressure Piping Systems Code looks to build on this tradition of excellence by expanding the scope of ASME codes and standards to provide end users with a robust approach for design and construction of non-metallic piping systems.”
The development of the new standards also reflect the growing international role of ASME standards. According to Mohinder Nayyar, chairman of the NPPS Standards Committee 2011-2014, the committee is considering best practices and requirements from various international references, in addition to sources in the United States.
The standards for thermoplastic and FRP piping systems are being developed to fill the unmet need for comprehensive documents in these areas. The committee expects them to gain acceptance in both the domestic and international industry.