Part 3 of the seven-part series on material selection for chemical process equipment focuses on select other materials beyond Metals (Part 1) and Plastics (Part 2). This summary of other materials includes Fiberglass Reinforced Plastics (FRP), Rubbers and Specialty Elastomers, Advanced Composites, and Technical Ceramics. Materials not in this Part 3 include products more applicable to project facility/area construction (e.g., concrete and wood), lightweight minor components (e.g., polymer foams and various material honeycombs), and more advanced/specialty materials not yet fully commercialized.

Fiberglass Reinforced Plastics (FRP)

FRP is a composite material using thermoset polymer resins and two- or three-dimensional fiber reinforcements with product-specific curing compounds, additives, and fillers to provide individual product properties. FRP composites have been used in chemical process equipment applications for more than 70 years and continue to develop with new resin and filler/additive materials and manufacturing techniques and technologies. FRP materials are used for tanks, tank shells, piping systems, ventilation hoods and ducting and blowers/fans and scrubbers, grating/stairs/ladders, structural shapes, and many custom wet process components. Similar to thermoplastics, application-appropriate, relatively lightweight FRP materials offer chemical resistance advantages over steels and stainless steels and for many cases over higher cost metals and alloys.  Depending on material market pricing and application specifics, FRP can be higher or lower installed cost* than stainless steels. FRP is an electrical insulator and does not present contact or galvanic corrosion  issues. FRP materials offer application-specific strength and temperature advantages over many thermoplastics.

FRP chemical process equipment can be manufactured through a range of processes, including molding, pultrusion molding, and several types of hand or automated lay-up processes. Different thermoset curing processes are also used, including combinations of catalysts or additives, heat, pressure, vacuum, or ultraviolet or other electromagnetic curing. FRP fabrication workmanship and process quality control are very important to production of quality, long-life FRP products.

FRP formulations using different resins provide for a broad range of excellent chemical resistance with some higher strength and temperature properties over commodity thermoplastics. Resin types range from more common polyester to more robust vinyl ester to higher strength epoxy resins. Other resin types include polyurethane, phenolics, and furans.  Fiber reinforcements, including fiberglass, carbon fiber, or aramid (e.g., Kevlar) fiber, give different strength properties. In favorable application conditions, vinyl ester or furan resin FRP pipe can be suitable for up to 200°F, and epoxy or phenolic resin FRP pipe can be suitable for up to 300°F.

FRP laminate products typically consist of layers of resin and fibers (glass or other materials) with layer-specific relative compositions; for example:

• Inner Laminate, or Chemical Barrier Layer (CBL): This layer is in contact with the process chemistry

(e.g., inside surface of a tank or pipe or duct) and protects the Structural Layer from chemical exposure. The Inner Laminate typically has a higher resin to fiber ratio (e.g., 70%|30%).

• Structural Layer: This layer provides load-carrying mechanical support and typically has a lower resin to fiber ratio (e.g. 30%|70%). FRP composite layers can also be built around metal or other material stiffeners or frames to provide additional strength.
• Top Layer: This layer, such as the CBL, has a relatively higher resin to fiber ratio to protect the Structural Layer from process chemistry splashes and spills.
• Gel Coat: This layer is prepared from the base resin and additives to provide a chemical resistant, high quality color finish.

FRP with glass-fiber reinforcing is lightweight (approximately 25% of steel) and typically provides approximately 50% of lengthwise tensile and flexural strength of steel. FRP strength in cross-wise direction is typically much lower than lengthwise strength (e.g., 25% to 30% of lengthwise strength), unless the specific FRP product is reinforced in the cross-wise direction.

In addition to catalysts and curing compounds, FRP additives can include fire retardants; UV protection; and surface enhancements, including abrasion resistance, traction enhancement, and static reduction.

FRP systems can be repaired in place without arc welding (an issue for some metal equipment in hazardous areas).  Coating, liner, and dual laminate applications for FRP and other materials are discussed in Part 4.

Rubbers and Specialty Elastomers

Rubbers and specialty elastomers are any of a wide range of polymer materials that differ from polymer plastics, as they are joined by chemical bonds to yield a cross-linked structure that provides for levels of elasticity where the materials can repeatedly deform under stress and return to original shape when the stress is removed.  Elasticity provides for good sealing performance over pressure and temperature variations.  Typical uses in process systems include gaskets and seals, belts and hoses, anti-vibration pads, and mounts. These materials have a broad range of chemical resistance, minimum service temperature (e.g., -10°F to -60°F) maximum service temperature (e.g., 175°F to 450°F), physical properties, and cost.

Rubbers

Rubbers are commonly grouped into oil resistant and non-oil resistant. Oil resistant rubbers include Nitrile rubber (NBR or Buna-N), Neoprene, Hypalon, Urethane, and Polysulfide.  Non-oil resistant rubbers include Natural Rubber, styrene-butadiene (SBR), and ethylene propylene diene terpolymer (EPDM). Various rubber compounds exhibit a broad range of chemical resistance and also vary with application range of temperature and physical properties such as hardness, compression resistance, and abrasion resistance.

Specialty Elastomers

There are  hundreds of specialty elastomers with a broad range in performance and price. Examples include silicone rubber, fluoroelastomer, FKM (e.g., Viton), and perfluoroelastomer, FFKM (e.g., Kalrez). Temperature and chemical resistance performance generally increase from standard silicone rubber to FKM to FFKM, and cost correspondingly increases significantly.

Technical Ceramics

Technical (i.e., Engineering or Advanced) ceramics include more conventional silicate ceramics used as electrical insulators (e.g., porcelains, magnesium silicates, and alkaline earth – silicon silicates), oxide ceramics (e.g., aluminum oxide, zirconium oxide, and mixed-oxide ceramics), and non-oxide ceramics (e.g., silicon carbide, silicon nitride, and aluminum nitride).

Technical ceramics are relatively chemically inert and can provide specialized high temperature service (e.g., above 1800°F) and mechanical property requirements (e.g., compressive strength, hardness, and abrasion resistance) for very challenging applications. Tensile strength for technical ceramics is typically a fraction of the material specific compressive strength. Technical ceramics are not widely used in surface finishing chemical process equipment but are important to some advanced manufacturing industry applications, including specialty pump and valve components, specialty tubing and piping, burner nozzles and refractory components, electrical components, and other custom process components. Specialty ultra-high temperature ceramics (UHTC) developed for NASA and aerospace applications have some of the highest known melting points of any materials and are used beyond application temperatures of nickel-based superalloys.

Advanced Composites

Advanced composites include polymer matrix composites (PMC), ceramic matrix composites (CMC), metal matrix composites (MMC), and carbon matrix composites. Advanced composites can contain fibers similar to FRP (e.g., glass, aramid, or carbon), and can use manufacturing techniques similar to FRP products. These materials can be relatively lightweight compared to metals (even significantly lighter than aluminum) and can be formulated to provide high axial and longitudinal strength properties similar to metals and metal alloys.  Advanced composites can provide relatively high range of application temperature (e.g., up to almost 500°F), chemical resistance, and fire retardance. Advanced composites can be very high initial cost, typically in the range of exotic metals and alloys, but can offer life-cycle cost advantages over lower performance materials. Advanced composites are used in newer aerospace, automotive (e.g., brakes, cylinder sleeves, bearings) military, and sporting goods applications. Applications are limited in surface finishing process equipment uses  and can require a very high level of up-front applications and design engineering.  Advanced composite materials, such as carbon + fiberglass or carbon + Kevlar, are commercially available as tubing, shaped tubing, and also as panels, plates, and angles. Metals can be deposited onto composite surfaces, an important application in the surface finishing industry, providing desired enhanced surface properties (see Part 4).

Next week, watch for Part 4: Material Selection for Chemical Process Equipment – Liner and Coating Systems. Part 4 provides information on a broad range of materials used for liners (plastics, metals, glass, ceramics, composites, etc.) and coating systems (plastics, epoxies, composites, etc.) to extend the application range of base materials.

* Specific metal alloy and FRP prices can vary significantly with market conditions.  Application specifics can result in a broad range of FRP resin and fiber/additive requirements that vary the FRP total installed cost.

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Integrated Technologies, Inc. is an industry-leading engineering, design, and consulting solutions firm based in Burlington, VT. We offer project planning and development, full-service engineering and design, project and construction management, and services during construction to the surfacing finishing and industrial manufacturing industries. 

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Part 2 of the seven-part series on material selection for chemical process equipment focuses on plastics. Plastics include a range of organic polymer structures that can include chlorine or fluorine and other functional groups. Plastics are commonly used in applications for tanks, pumps, piping and valving, ventilation systems, and miscellaneous equipment and components. Various plastics provide good to excellent chemical resistance for caustics, acids and some solvents that can be superior to even higher cost metals. In some applications with very aggressive process chemistries, fluoropolymer plastic heat exchangers are used instead of metal heat exchangers (although plastics require significantly larger heat transfer surfaces compared to metals). Factors including temperature, concentrations and combinations of chemistries, and mechanical stresses/loads  including fluid pressures, are important considerations for selecting specific plastics for chemical process equipment applications. Different proprietary and non-proprietary plastic formulations for a specific plastic type can provide significant variations in product purity, structure, temperature application range, and chemical resistance. Plastics are very light weight compared to metals, provide thermal and electrical insulation, and can be simple to form and machine. Plastic material prices can vary by more than an order of magnitude from commodity plastics up to more exotic fluoropolymer and imidized plastics. Individual plastic prices* can vary significantly with market demand and raw material supply. Some plastics used in surface finishing process applications include the following types:

Polyvinyl Chloride (PVC) and Chlorinated Polyvinyl Chloride (CPVC)

PVC and CPVC are relatively low cost and provide good chemical resistance for a range of acids, bases, and salt solutions. PVC is attacked by polar solvents. CPVC (modified PVC with chlorine content increased from ~57% to ~67%-74%) is higher in cost but provides added chemical resistance over PVC in many applications. CPVC is also suitable for higher temperatures up to 180°F to 210°F for some products and applications, compared to 140°F for PVC under favorable pressure and chemical exposure. CPVC also provides superior fire-resistance over PVC. PVC and CPVC are common materials for ventilation hoods and ducting up to application specific temperature and chemistry limits.  Metals, such as stainless steel (SS), or fiberglass reinforced plastic (FRP) composites with appropriate materials and reinforcement are needed for some higher temperature applications. The density of PVC is ~50% more than PP and HDPE, and PVC has some strength advantages over other common plastics. HDPE pipe walls must be 2.5 times thicker than PVC to achieve the same pressure rating for room temperature water applications, and the tensile and flexural strength of PVC are significantly higher than PP or HDPE.

Polypropylene (PP)

PP is used as a cost-effective material for tanks, including seamless tanks, and other process system equipment and components in a wide range of surface finishing applications. PP is also preferred over PVC and CPVC for piping and ventilation in many parts of the world. PP provides superior chemical resistance and high temperature resistance in many applications beyond PVC and is superior in chemical resistance over PVDF in some applications with strong bases and with some solvent and mixed chemical applications. PP has superior bending stiffness and tensile strength as compared to HDPE. PP has a Vicat heat distortion (softening) temperature in the range of ~289-305°F, compared to ~ 176°F for rigid PVC.  Different PP polymer formulations (e.g., homopolymer vs. copolymer) provide different properties, such as low temperature application range, impact strength, hardness, malleability, melting and softening points, and translucence. PP brittleness increases substantially more than HDPE or PVC or PVDF at temperatures approaching and below freezing.

Polyethylene (PE)

PE is available in a range of densities/molecular weights, providing different physical properties in addition to broad chemical resistance. PE can provide similar temperature and chemical resistance for many applications compared to PP (both are polyolefins).  PE has superior abrasion resistance to PP and PVC, with a sand-slurry method seven times higher than PP and over 50% more than steel.  Some common PE types include the following:

• Low-Density Polyethylene (LDPE) and Medium-Density Polyethylene (MDPE): LDPE is very flexible but relatively low in strength – it is commonly used for plastic sheeting. MDPE is stronger than LDPE and provides some additional chemical resistance.
• Cross-Linked Polyethylene (PEX or XLPE): The cross-link polymer bonds in this medium-to-high-density PE improve high temperature properties and enhance chemical resistance for some applications.
• High-Density Polyethylene (HDPE): HDPE provides significantly more strength and stiffness and higher temperature resistance than LDPE and MDPE and is easy to fabricate and weld. HDPE is available in sheet and pipe form and is molded into complex shapes.
• Ultrahigh Molecular Weight Polyethylene (UHMW): Due to a less-efficient molecular packing structure, the density of UHMW is slightly lower than HDPE. UHMW is less rigid and has ~78% tensile strength and ~55% flexural modulus of HDPE but provides superior impact resistance over HDPE. UHMW has a low coefficient of friction and is self-lubricating, making it excellent for parts exposed to friction and wear.

Polyvinylidene (PVDF)

PVDF is a relatively higher cost fluoropolymer thermoplastic that provides superior chemical resistance in many applications (strong bases are one exception) and has a significantly higher service temperature, ranging up to 250°F to 300°F in favorable conditions, compared to CPVC, PP, and HDPE. PVDF is almost twice as dense as PP. PVDF is available in piping, sheet, tubing, film, and plate form. Kynar® (one common group of PVDF plastics) can be homopolymer or copolymer and may also contain application specific additives (e.g., Red Kynar® has pigment added for ultraviolet (UV) protection). High purity 100% homopolymer PVDF is non-leaching and does not support growth of biological impurities, making it suitable for high and ultrapure applications.

Other Fluoropolymer Plastics

Polytetrafluoroethylene (PTFE) is a fluoropolymer plastic with excellent chemical resistance and high temperature resistance extending well beyond PVDF and other commodity plastics. A common brand name is Teflon. PTFE is not melt-processable. PTFE is primarily used as a high-performance coating and is featured more in Part 4 of this series. Perfluoroalkoxy (PFA) is a melt-processable fluorinated copolymer that provides chemical resistance and temperature performance similar to PTFE but at higher cost. Fluorinated ethylene propylene (FEP) copolymer has a slightly different structure than PTFE and is melt-processable but has reduced chemical resistance and temperature performance. FEP is lower cost than PTFE. Ethylene Tetrafluoroethylene Copolymer (ETFE) provides chemical inertness approaching PTFE and with superior melt-processability and mechanical properties beyond FEP and PFA. In addition to coating applications, various fluoropolymers are used in tubing for heat exchangers and other fluid applications with a combination of aggressive chemistries and elevated temperatures, including seals and gaskets and valve components. PTFE, FEP, and PFA are non-combustible, and PVDF and ETFE are self-extinguishing.

Imidized Plastics

These high cost, highest performance plastics include polyamide-imides and polyimides. Imidized plastics provide good to excellent chemical resistance and are superior to other plastics in combined high-temperature application range (up to 500°F) with high load bearing and wear performance. Imidized plastics are available as sheet, rod, or fabricated parts and are also used as a coating material. Example applications include bearings and bushings, pump and valve parts, and seals and specialty components in aerospace, electronics, and semiconductor industries.

Acrylics and Polycarbonates

Acrylic and polycarbonate plastics are used where clear, impact-resistant materials are needed for viewing ports, equipment enclosures/barriers, and other specialized applications. One common acrylic is Plexiglas. One common polycarbonate is Lexan. In addition to having different chemical resistance properties for select applications (e.g., polycarbonates provide superior resistance to chlorine bleach and hydrogen peroxide solutions), these clear plastics differ substantially in physical properties.  Polycarbonates are far superior in impact resistance, and acrylics provide superior resistance to scratching.

Additives and Fillers in Plastics

Plastic compositions vary with manufacturer-specific formulations, including ranging from pure homopolymers to varied copolymer structures, and may include various additives and fillers. For example, while homopolymer polypropylene contains only propylene monomers, copolymer polypropylene has ethylene incorporated into the polypropylene polymer chains either randomly (typically up to 6% ethylene) or in regular block patterns (typically 5% to 15 % ethylene). Some plastics, such as PVDF and PP, are provided in commercial high-purity form, and other plastics contain additives and/or fillers. For example, PVC stabilizers can include various metals or rare earths or metal-free compounds (e.g., newer technologies have moved away from lead and tin stabilizers).

A range of additives are used in various plastic products to aid in the polymer material production processes. These include plasticizers to improve flexibility and slip agents for easier release from molds. Additives are also used in plastics to enhance or modify plastic product properties, including long term stability, mechanical properties, chemical resistance, service temperature range, UV light resistance, resistance to biofouling, degree of opacity, product color, antistatic performance, electrical or thermal conductivity, and fire retardance.

Application Considerations for Plastics

With over 100 different grades of application-specific plastics used for chemical process equipment and systems, it is important to define technical design criteria and project cost and non-cost criteria to focus on candidate plastic materials that can be systematically evaluated vs. metals, other materials, and combinations of materials. Application specifics, including ranges and variation in chemical and temperature exposure and mechanical stresses over the design life, can significantly impact the service life of different plastics and impact life-cycle costs for chemical process equipment and process systems. Environmental sustainability is another consideration for evaluating different plastic options for chemical process equipment and components and for evaluating plastics vs. other materials.

Next week, watch for Part 3: Material Selection for Chemical Process Equipment – Other Materials. Part 3 provides information on fiberglass reinforced plastics (FRP), rubbers and specialty elastomers, and advanced composites. 

* For example, the polypropylene price increased ~65% between December and March 2017 and decreased ~ 26% between March and May 2017.

__________________________________________________

Integrated Technologies, Inc. is an industry-leading engineering, design, and consulting solutions firm based in Burlington, VT. We offer project planning and development, full-service engineering and design, project and construction management, and services during construction to the surfacing finishing and industrial manufacturing industries. 

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ITI’s GDPR Privacy Policy

If you’ve received this email, you opted in to receive the Integrated Technologies, Inc. email newsletter at some point in the past.  We only store your email address and name with the sole purpose of sending you our email newsletter on a quarterly basis.

You can change your mind at any time by clicking the unsubscribe link in the footer of this or any email you receive from us, or by contacting us at  [email protected].

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