As applications, risks and materials continue to evolve, it is vital that engineers stay abreast of revisions to the standards that govern non-metallic piping systems
Recent advancements in standards developed by the American Society of Mechanical Engineers (ASME; New York, N.Y.; www.asme.org) for Non-Metallic (NM) materials represent a significant step forward in the design and application of non-metallic piping systems (Figure 1), particularly for fiber-reinforced plastics (FRP) and dual-laminate materials.
FIGURE 1. Non-metallic piping systems, such as those constructed of fiber-reinforced plastics, are widespread across many industrial applications, including wastewater and sewage handling, electrochemical processes, mining and more
NM materials play a critical role in industries that handle hazardous chemicals and gases, offering a cost-effective and non-reactive alternative to traditional metals. This article examines updates to ASME NM.2 and NM.3.2 standards, detailing their impact on design requirements, material specifications and industry practices. Additionally, it explores the complementary role of standards from German organization Deutsches Institut für Normung (DIN; www.din.de) in addressing current gaps, providing a comprehensive perspective on the evolving landscape of non-metallic piping systems.
NM piping in electrolysis units
The electrolysis process involves handling chemicals and gases that are highly corrosive, flammable and often lethal. Commonly used metals, such as carbon steel and stainless steel, are incompatible with chemicals like chlorine, hydrochloric acid (HCl), potassium hydroxide (KOH) and sodium hydroxide (NaOH). Although metals like nickel can withstand these environments, their high cost makes them impractical. Non-metallic materials, particularly plastics, have become indispensable in the chlor-alkali industry due to their durability, cost-effectiveness, and resistance to chemical reactions.
Historically, ASME standards primarily addressed metallic piping systems. Recognizing the growing importance of non-metallic materials, the Nonmetallic Pressure Piping Systems (NPPS) committee was established in 2011 to create comprehensive standards for non-metallic piping. Before this, existing ASME guidance was limited to references in standards like RTP-1, BPVC Section III and Section X. The release of the first ASME non-metallic piping standards in 2018 marked a significant milestone. These standards — NM.1, NM.2 and NM.3 — cover thermoplastic piping systems, fiber-reinforced thermosetting resin piping systems and non-metallic material specifications, respectively. Together, they provide extensive guidelines for the design, material properties and specifications of non-metallic piping systems.
ASME NM.2
ASME NM.2 outlines the design requirements for FRP thermosetting resin and dual-laminate pressure-piping systems operating at pressures of up to 250 psig. It includes detailed chapters on design processes, material selection, fabrication, assembly and testing. Additional appendices guide specific design components, stress calculations and repair techniques.
Revision history of NM.2. The first edition of ASME NM.2 was published in 2018, with significant updates introduced in its 2020 revision. This included clarified definitions, updates to stress and flexibility calculations and the inclusion of eccentricity factors in buckling load assessments. New guidance on flange assembly, hydrostatic strength and material testing was also incorporated in the 2022 revision. However, dual-laminate piping systems, which integrate thermoplastic liners with FRP materials, remain outside the scope of NM.2. In the interim, DIN standards, such as DIN 16965 and 16966, provide valuable guidance for these applications. The most recent revision, NM.2-2022, was released in January 2023.
ASME NM.3.2
ASME NM.3.2 focuses on material specifications for reinforced thermoset plastics. It defines 18 specifications based on base materials, fitting types and construction methods, covering resins, glass fibers, thermoplastic elastomers and more. The standard also provides guidelines for special applications, such as corrosion-resistant or marine environments, and includes appendices detailing material marking, ASTM International references and approval processes for new materials.
Revision history of NM.3.2. The NM.3.2 standard, first published in 2018, has undergone significant updates. Its 2020 revision refined material classifications, expanded liner options, and added detailed specifications for filament-wound FRP, elastomeric seals and glass-fiber strands. These updates align NM.3.2 more closely with DIN 16965, which categorizes materials and dimensions for various pipe sizes. The most recent version, NM.3.2-2022, was released in January 2023.
Updates to NM standards
Since their introduction, NM standards have seen several updates and improvements. Notably, NM.2 underwent significant changes in its 2020 revision. Key updates included the addition and refinement of definitions to ensure greater clarity, as well as the thorough revision of Mandatory Appendix II. This updated appendix now incorporates weight and volume fractions of lamina, along with methods for calculating mechanical and physical properties based on lamina orientation (for instance, unidirectional, random and so on).
The calculation of pipe support loads for FRP piping systems was also enhanced. Eccentricity factors were introduced into buckling load calculations to provide more accurate results. Additionally, distinct definitions for hoop and axial tensile modulus of elasticity were included, offering clearer guidance for load calculations. To further assist users, an example problem — similar to those found in ASME B31 codes — was added to illustrate stress calculations.
A new definition for short-term hydrostatic strength was introduced, referencing ASTM D1599 testing standards to determine material tensile strength more accurately. Updates also addressed flange requirements, including specifications for waviness and drawbacks.
ASME PCC-1 is now referenced to clarify the assembly process for flanged connections. However, the standard still does not cover dual-laminate piping construction, which combines thermoplastic linings with FRP material. For now, DIN 16965 and DIN 16966 remain the primary guidelines for these systems, and further guidance is anticipated soon. The National Fire Code, provided by the National Fire Protection Association (NFPA; Quincy, Mass.; www.nfpa.org) continues to recognize DIN standards for non-metallic piping, with further details described in the following section.
NM 3.2, the standard for material specifications, also received significant updates. Material properties for filament-wound FRP were refined to include both polyester and vinyl ester classifications. New classification types and grades were added to encompass a broader range of liner materials. Dimensions and tolerances for various pipe sizes were introduced, aligning this standard with DIN 16965 classifications. Similar updates were made to specifications for machine-made FRP, contact-molded FRP, reinforced epoxy resins and elastomeric seals. Additionally, a dedicated specification for glass fiber strands was added, detailing their chemical composition and filament strand types to enhance clarity.
These advancements represent a substantial step forward in improving the precision, usability and comprehensiveness of the NM standards.
DIN 16965
DIN 16965 is a comprehensive standard divided into five parts, each outlining the dimensions for various types of FRP and dual-laminate pipes. It categorizes pipes into types A, B, D and E, specifying important dimensions, such as inner diameter (ID), outer diameter (OD) and layer thickness, based on pressure class, nominal size and material composition. The standard also details the required thickness for both the structural and lining layers, provides reference standards and includes a clear explanation of how to calculate the structural layer’s thickness.
Revision history of DIN 16965. The most recent versions of DIN 16965 Parts 1 and 2 date back to 1982, with the previous editions published in 1974. Parts 4 and 5 were also released in 1982, though Part 5 includes a correction issued in 2018, while the 1982 version remains the current standard. Part 3, originally published in 1971, has since been withdrawn. The specific revisions made between previous and current editions are not documented. Parts 1 and 2 indicate that the content was “completely revised” between the 1974 and 1982 editions, but the other sections of the standard provide no details on what changes were made.
DIN 16964 and 16966
DIN 16964 establishes the quality and testing standards for FRP pipes, while DIN 16966 Part 1 serves as the corresponding standard for fittings. These standards outline general requirements and reference guidelines for resins, liners and glass types used in production. Key criteria include hydrostatic and vacuum testing, dimensional tolerances, surface finish, chemical resistance, glass and styrene content, adhesive shear strength for dual laminates, fire performance and compliance with food-grade regulations. Additionally, the standards provide testing procedures to verify these requirements. Parts 2 through 8 of DIN 16966 further specify dimensions for various fitting types. It is important to note that DIN 16964 represents just one part of a comprehensive framework.
Revision history of DIN 16964 and 16966. DIN 16964 and DIN 16966 Part 1 were initially published in 1982, with their most recent updates released in 1988. Between these revisions, the standards introduced changes to adhesive shear strength values, specifically for type B fittings featuring a high-density polyethylene (PE-HD; or HDPE) liner. A new release of DIN 16965, replacing all old versions of DIN 16964, 16965 and 16966, is anticipated in 2026.
Closing thoughts
Both ASME and DIN standards permit the use of polyester resin (including vinyl ester), as well as various thermoplastic and thermoset liner materials. DIN provides a predefined list of approved liners and specifies that “the use of other liner materials shall be subject to agreement between purchaser and manufacturer.” ASME, on the other hand, allows for polyester, epoxy and several other thermoset resin liners, depending on the construction method. For thermoplastic liners, ASME leaves material selection to the user. Additives such as styrene, fillers, dyes and flame retardants must be agreed upon by both the purchaser and manufacturer, as neither standard dictates use (Figure 2).
FIGURE 2. Engineers tasked with specifying and purchasing piping systems and components must communicate with manufacturers regarding any additives, such as dyes, fillers, flame retardants and so on
The ASME NM committee has made significant strides in updating its standards to accommodate a broader range of plastic materials. However, it still falls short in addressing certain applications, such as dual laminates, which are commonly used in the electrolysis process. Until clearer ASME guidance is available for these materials, DIN standards offer a valuable alternative to bridge the gap. ■
Edited by Mary Page Bailey
Authors
Anthony Galvan is a senior mechanical engineer at thyssenkrupp Nucera USA (Email: houston@thyssenkrupp-nucera.com) based in Houston with experience in piping and equipment design across the energy and industrial sectors. He holds a B.S. in mechanical engineering and has worked with both metallic and non-metallic piping systems. His current work focuses on implementing electrolysis technology for the chlor-alkali and alkaline water electrolysis sectors.
Avinash Kolla is a principal engineer with thyssenkrupp nucera USA Inc., leading the Piping & Layout Engineering group. He has years of experience dealing with piping issues, such as piping vibration, flow simulations, static and dynamic stress analyses and also pipe material specifications. He currently serves as a member of the Design (SG-B) subgroup of ASME B31.3 process piping committee. He is also a Professional Engineer (P.E.) in six US states and one province in Canada.