FRP Fabrication and Installation Guide: Ductwork, Piping, and Tanks
FRP fabrication and installation for corrosive exhaust requires different techniques than working with thermoplastics or metals because FRP is a thermoset composite — once cured, it cannot be re-melted and re-formed like PP or PVC. Every joint, fitting, and repair must be laminated using the same resin and glass reinforcement system as the original fabrication. The process — selecting the correct resin for the chemical environment, choosing the appropriate glass reinforcement, fabricating the laminate by contact molding or filament winding, and curing to full mechanical strength — determines whether the FRP component provides 20 to 30 years of service in corrosive exhaust or chemical storage service or fails within 2 to 5 years from improper material selection or fabrication defects. This guide covers resin and fiber selection, fabrication methods for ductwork, piping, and tanks, quality control testing, safety requirements, and installation standards for FRP in corrosive exhaust systems. For specific installation procedures, see our FRP duct installation, FRP tank installation, FRP pipe installation, and FRP welding procedure guides.
Key Takeaways
- FRP fabrication and installation for chemical service uses thermoset resin that cannot be re-melted — all field joints and repairs require hand lay-up lamination using the same resin and glass system as the original fabrication. This is fundamentally different from thermoplastic (PP, PVC) fabrication where joints are heat-welded.
- Resin selection is the most critical decision in FRP fabrication for chemical service. Polyester resin ($25-$45/kg) is suitable for general service up to 80°C, vinyl ester ($35-$60/kg) for chemical exhaust up to 120°C, and epoxy ($50-$90/kg) for high-temperature or high-strength applications above 120°C. Using the wrong resin causes the laminate to degrade within 6 to 18 months.
- Three fabrication methods dominate FRP production: contact molding (hand lay-up) for low-volume custom components, filament winding for high-strength pipe and tank walls, and resin transfer molding (RTM) for complex shapes with high dimensional accuracy. The method determines the glass content, mechanical properties, and cost of the finished component.
- Quality control in FRP fabrication requires three tests: visual inspection for voids and dry spots, Barcol hardness testing (target 35-55 on the 934-1 scale for cured polyester and vinyl ester), and spark testing at 10,000 to 20,000 volts per mm of laminate thickness for pinhole detection in the corrosion liner.
- The installed cost of FRP fabrication and installation for ductwork for corrosive exhaust is $80 to $200 per kg of fabricated weight — lower than 316L stainless steel ($150 to $400 per kg) and competitive with lined carbon steel when the total lifecycle cost including corrosion maintenance is considered. FRP ductwork requires no external corrosion protection, no internal lining (the FRP laminate itself is the corrosion barrier), and no cathodic protection.
FRP Material Overview: Resins, Fibers, and Laminate Construction
FRP fabrication and installation starts with material selection, not fabrication technique, not fabrication technique. The resin determines the chemical resistance, temperature limit, and mechanical properties of the finished laminate. The glass reinforcement determines the strength, stiffness, and impact resistance. The liner — the inner layer that contacts the chemical environment — must be chemically resistant to the specific exhaust or chemical stream. Selecting the wrong resin for the chemical service causes laminate degradation that no fabrication skill can compensate for.
Resin Types and Selection Criteria
Three resin types are used in FRP fabrication for corrosive exhaust systems: unsaturated polyester, vinyl ester, and epoxy. Polyester resin is the most economical option ($25 to $45 per kg) and provides adequate chemical resistance for general exhaust applications at temperatures up to 80°C. Polyester is suitable for exhaust streams containing dilute acids, alkalis, and organic compounds at low concentrations. Two polyester grades are available: orthophthalic (general-purpose, lowest cost) and isophthalic (improved chemical and water resistance, 15 to 25 percent higher cost than orthophthalic).
Vinyl ester resin ($35 to $60 per kg) is the standard for chemical exhaust systems because it combines good chemical resistance across a broad range of acids, alkalis, and organic compounds with a higher maximum operating temperature of 120 to 130°C. Vinyl ester is approximately 70 percent of all resin used in FRP fabrication for chemical exhaust. The vinyl ester molecule has terminal methacrylate groups that provide corrosion resistance superior to polyester while maintaining handling characteristics that are easier than epoxy. For exhaust systems handling aggressive chemicals at elevated temperatures — HCl above 60°C, H₂SO₄ mist, organic solvents — vinyl ester is the minimum recommended resin.
Epoxy resin ($50 to $90 per kg) provides the highest chemical resistance and mechanical strength of the three resin types, with a maximum operating temperature of 150 to 180°C depending on the specific epoxy formulation and cure cycle. Epoxy is used for high-temperature exhaust systems, for FRP components that carry corrosive liquids at elevated temperatures, and for applications requiring maximum bond strength (structural repairs, high-pressure piping). Epoxy requires more careful handling than polyester or vinyl ester — the two-part resin-hardener system must be mixed in precise ratios, and the cure time is longer (24 to 48 hours versus 4 to 12 hours for vinyl ester).
Glass Reinforcement Types
E-glass (electrical-grade glass) is the standard reinforcement for FRP fabrication. It provides good strength at low cost. C-glass (chemical-grade glass) has improved acid resistance and is used for the surface veil layer — the resin-rich inner layer that provides the primary corrosion barrier. The surface veil (30 to 50 g/m²) is the first layer applied in the laminate sequence and must be C-glass for chemical service. Chopped strand mat (CSM, 300 to 600 g/m²) provides isotropic strength in all directions and is the primary structural layer. Woven roving (400 to 800 g/m²) provides directional reinforcement for applications requiring high tensile strength in specific orientations. The standard laminate sequence for chemical service is: C-glass veil (corrosion barrier) → CSM (structural layer) → woven roving (if required) → CSM (surface layer). This sequence ensures the corrosion barrier is protected behind the surface layers and the structural laminate carries the mechanical load.
FRP Fabrication Methods: Contact Molding, Filament Winding, and RTM
Three primary fabrication methods are used in FRP fabrication and installation for corrosive exhaust service. Each method produces a different laminate structure with different mechanical properties, dimensional accuracy, and cost. The fabrication method selection depends on the component geometry, production volume, mechanical requirements, and budget.
Contact Molding (Hand Lay-Up)
Contact molding, also called hand lay-up, is the simplest and most widely used FRP fabrication method.
Layers of glass reinforcement are placed manually in a mold, and liquid resin is applied with rollers or brushes until the glass is fully wetted. The laminate is allowed to cure at ambient temperature (typically 4 to 12 hours for polyester or vinyl ester at 25°C). Contact molding produces a glass content of 30 to 40 percent by weight — lower than filament winding (60 to 70 percent) — which means the laminate is less strong but more corrosion-resistant because of the higher resin content. Contact molding is used for low-volume custom fabrications: duct fittings (elbows, tees, reducers), tank nozzles and manways, scrubber components, and small-diameter pipe below 300 mm. The tooling cost for contact molding is low ($500 to $5,000 per mold) but the labor cost per part is higher than automated methods. A typical contact-molded FRP duct section costs $80 to $200 per meter for 300 mm diameter, depending on the resin type and wall thickness.
Filament Winding
Filament winding is an automated process where continuous glass fibers are wound onto a rotating mandrel at a controlled angle (typically 55 degrees for pressure pipe) while resin is applied. The process produces a laminate with 60 to 70 percent glass content by weight — nearly double that of contact molding — providing higher tensile strength and lower material cost per unit of strength. Filament winding is used for high-production-volume cylindrical components: straight pipe sections (50 mm to 4,000 mm diameter), tank cylindrical walls, and large-diameter duct straight sections. The tooling cost for filament winding is $10,000 to $100,000 per mandrel, but the per-part cost is lower than contact molding for production volumes above 50 units. Filament-wound pipe for corrosive exhaust at 50 psi rating costs $40 to $120 per meter for 150 mm diameter — approximately 40 percent less than contact-molded pipe of the same size because of the higher glass content and lower resin consumption.
Resin Transfer Molding (RTM)
RTM uses a closed mold system where dry glass reinforcement is placed in the mold and liquid resin is injected under pressure (30 to 100 psi). RTM produces components with controlled thickness, smooth surfaces on both sides, and consistent glass-to-resin ratios. RTM is used for complex FRP components that require high dimensional accuracy: flanges, valve bodies, pump casings, and equipment housings. The tooling cost for RTM is higher than contact molding ($5,000 to $50,000 per mold) but the surface finish and dimensional repeatability are superior. RTM is rarely used for standard ductwork or piping because the mold cost cannot be justified for linear products.
FRP Duct Fabrication: Round, Rectangular, and Fittings
FRP duct fabrication for corrosive exhaust systems uses contact molding (for fittings and custom shapes) and filament winding (for straight round sections). The duct is fabricated with a corrosion liner (2.5 to 3.5 mm thick) that provides the chemical barrier, a structural laminate that provides the mechanical strength, and an exterior gel coat that provides UV and weather resistance for outdoor installations. The fabrication method affects the duct pressure rating, weight, and cost. Standard FRP duct sections are fabricated in 3 to 6 meter lengths for diameters from 50 to 2,000 mm.
Round FRP duct is fabricated by filament winding for straight sections and by contact molding for fittings.
Filament-wound straight sections are produced with a 2.5 to 3.5 mm corrosion liner followed by the structural windings to the specified wall thickness.
Standard wall thicknesses for round FRP duct in corrosive exhaust service: 4.
8 mm for 150 mm diameter, 6.4 mm for 300 mm, 7.9 mm for 600 mm, and 9.5 mm for 900 mm and above. The duct is supplied with integrally molded flanges at both ends — the flange face is built up from additional laminate layers during fabrication to create a flat sealing surface. The flange face must be machined flat after cure to ensure uniform gasket contact — a flange face that deviates by more than 1 mm over the full flange width causes uneven gasket compression and leaks at the bolt locations. Flanges are typically supplied with bolt holes drilled to match the mating duct or valve flange pattern. The bolt hole circle and bolt size follow standard duct flange dimensions — for 150 mm duct: 4 bolts at 12 mm diameter on 180 mm bolt circle; for 300 mm duct: 6 bolts at 12 mm on 270 mm bolt circle; for 600 mm duct: 8 bolts at 16 mm on 375 mm bolt circle.
Rectangular FRP duct is fabricated by contact molding — flat panels are laminated on a flat mold, then assembled into a rectangular shape using corner joints that are laminated on both the interior and exterior.
Rectangular FRP duct is more labor-intensive than round duct ($150 to $350 per meter versus $80 to $200 per meter) and requires additional reinforcement at the corners to prevent deflection under the exhaust system static pressure. The corner reinforcement is typically a fillet of resin and chopped strand mat applied to the interior corner joint, with a minimum radius of 25 mm to prevent stress concentration. For rectangular duct widths above 600 mm, internal cross-bracing (tie rods or stiffening ribs) is required to prevent the flat side panels from bowing outward under the static pressure of the exhaust fan. The tie rods are FRP rods or strips bonded across the duct interior at 600 mm intervals. The pressure drop penalty from internal bracing must be included in the system static pressure calculation — each tie rod adds approximately 0.05 to 0.10 inches W.G. pressure drop depending on the duct velocity.
Fittings — elbows, tees, reducers, transition pieces — are fabricated by contact molding regardless of the straight-duct fabrication method. A 90-degree elbow is fabricated using a segmented mold (for small diameters) or by fabricating a mitered section with laminated joints (for large diameters above 600 mm). The elbow fabrication labor is 2 to 4 times the labor for an equivalent length of straight duct, which is why fitting costs are 2 to 3 times the per-meter cost of straight duct. For complex duct routing with multiple fittings, the fitting cost can account for 40 to 60 percent of the total duct system fabrication cost. All fittings must include the same corrosion liner and laminate thickness as the adjacent straight duct sections to maintain uniform chemical resistance throughout the duct system. Fittings with sharp interior corners (such as square-edged reducers or mitered elbows) must have the interior corners radiused to a minimum of 25 mm during fabrication to prevent turbulence and condensate accumulation at the sharp edge.
FRP Pipe Fabrication: Filament-Wound Pipe and Joint Methods
FRP pipe for corrosive chemical service is almost exclusively filament-wound because the automated winding process produces consistent wall thickness and higher strength than contact-molded pipe. The pipe is fabricated with a corrosion liner (2.5 to 3.5 mm of C-glass veil in a resin-rich matrix), followed by a structural winding, and for buried service an exterior corrosion barrier. The joint method is critical because the joint must maintain the chemical resistance of the liner and the mechanical strength of the structural laminate across the pipe-to-pipe connection.
Filament-wound pipe fabrication. The pipe is wound on a steel mandrel coated with release agent. The corrosion liner is applied first, typically 2.5 to 3.5 mm thick. After the liner cures, the structural layers are wound at a controlled angle of 55 degrees for pressure pipe operating at 50 to 200 psi. This angle creates equal strength in hoop and axial directions. For low-pressure exhaust piping below 20 inches W.G., the winding angle can be increased to 70 to 80 degrees to reduce wall thickness and cost. Standard pipe diameters range from 50 to 1,200 mm with pressure ratings of 50, 100, 150, and 200 psi.
Bell-and-spigot adhesive joint. This is the most common joining method for FRP pipe, accounting for 75 percent of all FRP pipe joints. The bell end is fabricated with an enlarged diameter during winding, and the spigot end is machined to fit inside the bell with an annular gap of 1.5 to 3.0 mm. The joint is assembled with a thixotropic adhesive of the same resin system as the pipe. Cure time is 24 hours at 25C before pressure testing, 48 hours at 15C. Below 10C the adhesive does not cure, requiring a heated enclosure for winter assembly.
Butt-and-wrap laminated joint. Used where the pipe cannot be rotated for bell-and-spigot assembly. The ends are aligned with a 3 to 6 mm gap, a backing strip is bonded inside, and multiple laminate layers are applied over the exterior. The number of wrap layers must equal the number of structural layers in the pipe wall. Joint thickness must match the pipe wall within 1 mm. Cost is 0 to 00 for 150 mm pipe, 3 to 5 times the cost of a bell-and-spigot joint but providing full-strength continuity.
FRP Tank Fabrication: Vertical, Horizontal, and Custom Configurations
FRP storage tanks for corrosive chemicals are fabricated using a combination of filament winding (for the cylindrical wall) and contact molding (for the bottom, top, nozzles, and internal components). The tank wall is constructed with the same corrosion liner (2.5 to 3.5 mm of C-glass veil in a resin-rich matrix) followed by a structural laminate, but the wall thickness is significantly greater than FRP pipe or duct because the tank wall must resist the hydrostatic head of the stored liquid. The hydrostatic pressure at the bottom of a 4-meter tall tank filled with liquid specific gravity 1.2 is approximately 5 psi — modest compared to pipe pressure ratings, but the tank diameter of 2 to 4 meters means the total hoop stress in the wall is large and the laminate must be thick enough to prevent excessive wall deflection that would crack the corrosion liner.
Vertical FRP tanks are the most common configuration for chemical storage, accounting for approximately 80 percent of FRP tank fabrications.
The cylindrical wall is filament-wound on a steel mandrel at a winding angle of 55 to 75 degrees from the horizontal, depending on the ratio of hoop stress to axial stress. The wall thickness varies with the tank diameter and height: a 2-meter diameter by 3-meter tall vertical tank carrying liquid with specific gravity 1.2 requires a wall thickness of 8 to 10 mm; a 3-meter by 4-meter tank requires 12 to 16 mm; and a 4-meter by 5-meter tank requires 16 to 20 mm. The bottom of the vertical tank is a flat or slightly dished FRP plate fabricated by contact molding and bonded to the cylindrical wall with additional laminate layers at the bottom-to-wall joint. The top of the tank can be open (atmospheric vent), domed (pressure-rated, typically 3 to 5 psi), or flat with reinforcing beams. The domed top is fabricated by contact molding over a spherical mold and bonded to the cylindrical wall with the same laminate procedure as the bottom joint.
Nozzles on vertical FRP tanks — for inlet, outlet, drain, vent, and instrument connections — are fabricated from FRP pipe sections (typically 2 to 6 inches diameter, Schedule 40 or 80 wall thickness) and are laminated into the tank wall during fabrication.
The nozzle-to-wall joint is the most stress-concentrated point on an FRP tank. The joint is reinforced by a buildup of additional laminate layers around the nozzle circumference — called a reinforcing pad. The pad diameter must be at least 3 times the nozzle diameter, and the pad thickness must be 50 to 100 percent of the tank wall thickness. The nozzle must extend at least 150 mm inside the tank (for liquid outlet nozzles) or be flush with the tank wall (for vent and instrument connections). Manways (18 to 24 inch diameter openings for personnel access) are fabricated with a reinforced flange ring that is laminated into the tank wall. The manway cover is a separate FRP plate with a gasket seal, bolted to the flange ring. The cost of a manway fabrication — including the cutout, flange ring, and cover — is $200 to $500 for a standard 18-inch manway on a 3-meter tank.
Horizontal FRP tanks are used where headroom is limited (installations with ceiling height below 4 meters) or where the tank diameter exceeds the available vertical space for transportation.
The cylindrical wall is filament-wound, and the ends are dished or hemispherical heads fabricated by contact molding.
Horizontal tanks require saddle supports that cradle the tank across the full saddle contact area — the saddle must have a minimum 120-degree contact arc to distribute the filled tank weight without overstressing the cylinder wall.
The saddle supports are typically FRP or steel with a rubber or PTFE liner at the contact surface. The ends of horizontal tanks must be stiffened with internal ring stiffeners (fabricated from FRP and bonded to the wall) if the tank diameter exceeds 2 meters, to prevent the tank from ovalizing under its own weight at the saddle supports. Horizontal FRP tanks are fabricated in capacities from 500 to 20,000 liters. For both vertical and horizontal tanks, internal baffles — required for mixing applications or to prevent surge in mobile tanks — must be fabricated from FRP and bonded to the tank wall using the same laminate sequence as the wall structure. Baffles must have bottom cutouts (at least 50 × 50 mm) to allow complete drainage and cleaning, and the baffle-to-wall joint must be radiused (minimum 25 mm radius) to prevent stress concentration at the joint.
FRP Installation Standards: Supports, Thermal Expansion, and Field Joints
FRP installation for corrosive exhaust differs from steel or plastic pipe installation in three critical areas: support spacing is closer, thermal expansion is higher, and field joints require temperature-controlled lamination. An FRP duct or pipe with a modulus of 10 GPa (versus 200 GPa for steel) requires supports at 1.5 to 3 meter intervals depending on diameter and temperature, compared to 4 to 6 meters for steel. The coefficient of thermal expansion for FRP (15 to 30 × 10⁻⁶/°C) is 2 to 3 times that of steel, requiring expansion joints or loops for long straight runs. Field joints — butt-and-wrap laminated connections — must be made at temperatures above 15°C, and the joint must cure for 24 hours before the system can be pressure tested or placed in service.
Support spacing. FRP duct and pipe support spacing follows the manufacturer design tables based on pipe diameter, wall thickness, operating temperature, and liquid specific gravity (for pipe) or duct weight plus any internal condensation load (for duct).
For standard FRP pipe at 20°C carrying water, support spacing ranges from 2.1 m for 50 mm diameter to 3.6 m for 300 mm diameter. At 80°C with the same pipe, the required support spacing reduces to 1.5 m to 3.0 m because the resin stiffness decreases at elevated temperature — the flexural modulus of vinyl ester at 80°C is approximately 70 percent of its room-temperature value. For FRP ductwork handling exhaust gas (negligible weight compared to liquid), the support spacing can be 10 to 15 percent wider than the pipe values for the same diameter. All supports must have a minimum 120-degree contact arc with the pipe or duct surface. A flat steel member supporting the pipe creates a line-contact stress concentration — use a pipe saddle or wrap the support with a 3 to 6 mm thick rubber or PTFE liner to distribute the load across the full 120-degree arc.
Thermal expansion. A 30-meter straight run of FRP pipe operating at 80°C with an installation temperature of 20°C expands by 27 to 54 mm (15 to 30 × 10⁻⁶/°C × 30 m × 60°C).
This expansion must be accommodated by expansion loops, expansion joints, or directional changes in the piping layout. Expansion loops are the preferred method for FRP — a U-shaped loop in the piping layout that flexes to absorb thermal movement. The loop length must be a minimum of 10 times the pipe diameter for a temperature differential of 60°C, increasing to 15 times for higher differentials. The loop must be fabricated from straight pipe sections with laminated elbows — the loop itself is not subject to internal pressure stress in the same way as a straight pipe run, but the elbows must be reinforced with additional laminate layers at the outer radius to handle the bending stress from thermal movement. For confined spaces where expansion loops cannot fit, use PTFE-lined expansion joints with control rods. The expansion joint must have a travel rating of at least 50 mm and must be anchored at one end to force the expansion to be absorbed at the joint location.
Field joint requirements. Field joints in FRP systems — butt-and-wrap laminated connections between duct or pipe sections — must be made at ambient temperatures above 15°C.
Below 15°C, the resin cure slows to the point where the joint may not reach full cure within 48 hours, leaving the bond interface at 40 to 60 percent of design strength.
The laminator must verify the surface temperature of the FRP at the joint location (not the ambient air temperature) using an infrared thermometer — the FRP surface absorbs radiant heat from sunlight or reflects cold from the building structure, creating a temperature difference of 5 to 10°C from ambient. The surface must be dry — any moisture on the FRP surface at the joint location creates microscopic steam bubbles at the bond line during the exothermic cure reaction, causing porosity that reduces bond strength by 30 to 50 percent. After lamination, the joint must cure for a minimum of 24 hours at 20°C or above before any mechanical load is applied. For buried FRP pipe, the joint must cure for 48 hours before backfill — the backfill load on an uncured joint causes the laminates to separate at the bond line.
Quality Control and Testing for FRP Fabrication
Quality control in FRP fabrication is essential because defects are not visible from the exterior of a finished component — a void in the corrosion liner or a dry glass spot in the structural laminate is hidden inside the laminate until it causes failure. Three quality control tests are standard for FRP fabrication in corrosive exhaust service: visual inspection (the simplest check), Barcol hardness testing (cure verification), and spark testing (pinhole detection in the corrosion liner).
Visual inspection is performed during fabrication (checking for dry spots, air bubbles, and resin-starved areas) and after cure (checking for surface defects, dimensional accuracy, and flange face condition).
The laminate must show consistent color and surface finish across the entire component — discolored areas indicate incomplete cure or excessive catalyst concentration.
Burrs, sharp edges, or rough surfaces must be ground smooth and sealed with resin before the component is placed in service. Barcol hardness testing per ASTM D2583 uses a handheld impressor that measures the surface hardness of the cured laminate. The acceptable range for cured polyester and vinyl ester is 35 to 55 on the 934-1 scale. Readings below 35 indicate incomplete cure — the component must be post-cured at 50 to 65°C or allowed additional room-temperature cure time. Spark testing (high-voltage holiday detection) uses 10,000 to 20,000 volts per millimeter of laminate thickness to detect pinholes, cracks, and thin spots in the corrosion liner. The spark jumps from the probe to the laminate surface at any location where the liner is compromised. The corrosion liner must pass spark testing at 100 percent of the test voltage over the full surface area before the component can be placed in chemical service. For components with a 3 mm corrosion liner, the spark test voltage is 30,000 to 60,000 volts. Any location where the spark jumps is marked, ground out to sound laminate, repaired with the same resin and glass system, and re-tested.
Safety in FRP Fabrication and Installation
FRP fabrication and installation involves hazardous materials that require specific safety precautions. The resin, catalyst, and solvents used in FRP fabrication present three primary hazards: styrene vapor exposure (from polyester and vinyl ester resins), MEKP catalyst handling (explosion risk), and grinding dust (respiratory hazard). Each hazard has established exposure limits and control methods.
Styrene exposure. Styrene monomer is the volatile component of polyester and vinyl ester resins. The OSHA permissible exposure limit (PEL) for styrene is 20 ppm as an 8-hour TWA, with a STEL of 40 ppm over 15 minutes. At 50 to 100 ppm, styrene vapor causes eye and respiratory irritation, headache, and dizziness. Control styrene exposure with local exhaust ventilation (capture velocity of 0.5 m/s at the resin surface) and NIOSH-approved organic vapor respirators. For enclosed work areas (tank interiors, confined spaces), use forced-air ventilation with a minimum of 6 air changes per hour and continuous styrene monitoring with a photoionization detector.
MEKP catalyst handling. Methyl ethyl ketone peroxide (MEKP) is the catalyst used for polyester and vinyl ester resins. MEKP is an organic peroxide that decomposes explosively when heated above 60°C, contaminated with accelerators (cobalt naphthenate), or shocked. Store MEKP in its original container at 10 to 25°C, separated from resin and accelerators by at least 3 meters or a fire-rated barrier. Never pour unused MEKP back into the original container — contamination of the bulk container causes explosive decomposition. Dispense MEKP using dedicated polyethylene or polypropylene equipment — never use metal containers or tools because MEKP reacts with most metals to form explosive metal peroxides. Grinding dust. Grinding cured FRP produces dust containing glass fibers and respirable crystalline silica. Control grinding dust with wet grinding (reduces airborne dust by 80 to 90 percent) or local exhaust ventilation (HEPA vacuum at the grinding tool). All personnel within 3 meters of grinding must wear N95 or P100 respirators and full-coverage goggles.
FRP Fabrication and Installation — FAQ
What is the difference between FRP and PP for corrosive exhaust ductwork?
In FRP fabrication and installation, FRP is a thermoset composite — once cured, it cannot be re-melted. PP is a thermoplastic that can be heat-welded. FRP has higher strength-to-weight than PP (tensile strength 150 to 300 MPa for FRP versus 25 to 35 MPa for PP) and higher maximum temperature (120°C for vinyl ester FRP versus 80°C for PP). PP is lower cost and easier to fabricate in the field. FRP is preferred for higher temperatures, larger diameters above 600 mm, and higher strength requirements.
What resin should I use for FRP in acid exhaust?
Vinyl ester resin is the standard for acid exhaust systems up to 120°C. For dilute acid exhaust below 80°C, isophthalic polyester is adequate at lower cost. For concentrated acid or mixed chemical exhaust above 120°C, use epoxy resin.
How is FRP ductwork fabricated?
Straight round duct sections are fabricated by filament winding. Fittings (elbows, tees, reducers) are fabricated by contact molding (hand lay-up). Rectangular duct is fabricated by contact molding of flat panels assembled into the rectangular shape. All FRP duct includes a corrosion liner (2.5 to 3.5 mm thick) of C-glass veil in a resin-rich matrix.
What is spark testing and why is it required for FRP?
Spark testing (high-voltage holiday detection) uses 10,000 to 20,000 volts per millimeter to detect pinholes in the corrosion liner. The corrosion liner must be free of pinholes to prevent chemical attack on the structural laminate. Spark testing is mandatory for all FRP components in chemical service.
Can FRP be repaired if damaged?
Yes. Minor surface damage (scratches, gel coat cracks) can be repaired by grinding out the damaged area, cleaning with acetone, and applying new resin and glass reinforcement. Structural damage (through-laminate cracks, impact damage) requires taper grinding the damaged area to a 12:1 slope and rebuilding the laminate layer by layer. All repairs must be spark tested after completion.
How long does FRP fabrication take?
Contact-molded components require 4 to 12 hours cure time at 25°C before handling and 24 to 48 hours before full chemical service. Filament-wound pipe cures faster — the winding and cure cycle for standard pipe is 1 to 4 hours per section. Post-cure at 50 to 65°C may add 8 to 12 hours for components in high-temperature chemical service.
Conclusion: Fabricate and Install FRP for Reliable Corrosive Exhaust Service
FRP fabrication and installation for corrosive exhaust ductwork, chemical piping, and storage tanks requires a different skill set than working with thermoplastics or metals. The key differences — thermoset material that cannot be reheated, close support spacing, temperature-controlled field joints, and spark-tested corrosion liners — must be understood by everyone involved in specifying, fabricating, and installing FRP components. When correctly fabricated and installed, FRP provides the longest service life of any material for corrosive exhaust systems at temperatures up to 120°C (vinyl ester) or 150°C (epoxy), with lower total lifecycle cost than stainless steel or lined carbon steel in aggressive chemical environments.
For detailed installation procedures for FRP components, see our FRP duct installation guide, FRP tank installation guide, FRP pipe installation guide, and FRP welding procedure guide. For assistance with FRP fabrication and installation for your chemical exhaust system, contact our applications engineering team at xicheng023@outlook.com or visit our contact page.