Part 3: Material Selection for Chemical Process Equipment – Other Materials

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.