Pipe & Fittings

Fiberglass-reinforced thermoset plastic pipe, commonly referred to as FRP pipe, is frequently chosen for corrosive process systems. This preference is driven by several key factors:

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• Customizable for diverse corrosion-resistant requirements
• Lightweight (weighs less than 20% of steel and only 10% of concrete)
• Outstanding strength-to-weight ratio (stronger than steel on a weight basis)
• Superior low friction coefficient (more than 25% better than steel)
• Excellent dimensional stability with low thermal conductivity, leading to insulation cost savings
• Reduced long-term maintenance expenses

A comprehensive analysis of the system's total cost, incorporating all these factors, often indicates that fiberglass FRP pipe offers cost advantages over steel, and even greater savings when compared to alternative alloys.

Composites USA specializes in the manufacturing of hand lay-up and filament wound FRP pipe utilizing all commercially recognized resin systems, including polyester, vinyl ester, furan, phenolic, and epoxy thermoset resin systems. Resin systems and reinforcements are customized to suit specific applications. Materials compliant with FDA standards are also available, as are flame-retardant and dual containment FRP piping systems.

Designing any pipe system necessitates a consideration of various factors. Key aspects such as corrosion allowances, operating pressure, temperature, abrasion, flammability, and electrical conductivity must be analyzed. Mechanical design assesses the pipe's strength, support requirements, thermal expansion considerations, burial loads, as well as environmental factors like wind, snow, and seismic loads. Laminate analysis and, when necessary, finite element analysis contribute to the overall FRP pipe design solution.

The system evaluation employs traditional methods, integrating the appropriate physical properties relevant to the specified fiberglass system. A standard specification for fiberglass piping can also be found in this catalog binder.

DESIGN CONSIDERATIONS:

The process design significantly impacts the fiberglass FRP pipe design. The process typically dictates the necessary corrosion liner resin selection and thickness, along with the required design and operating temperatures, pressures, and vacuum conditions.

After establishing these criteria, the mechanical design of the fiberglass pipe laminate structure commences. The laminate design will weigh the economic advantages of various resin and reinforcement properties to satisfy the defined process design. Ultimately, the complete system is scrutinized for suitable support, thermal expansion stresses, and compliance with relevant codes.

The sections that follow will outline critical relationships pertaining to fiberglass FRP piping. A life cycle cost comparison will ultimately illustrate the economic efficiency of fiberglass piping as opposed to steel.

Process Design

Corrosion Requirements:

The potential concentration limits of the process stream must be assessed for chemical corrosion resistance, taking temperature into consideration. Recommendations from the resin manufacturer should always be solicited wherever possible. Fiberglass pipes generally evade many corrosion issues typically associated with metal pipes, such as galvanic, aerobic, intergranular corrosion, or pitting.

Resin Selection:

As highlighted earlier, specific recommendations should always be sought. A wealth of data exists for several resin systems, while corrosion data for others may be somewhat limited. General-purpose polyester resins should generally be avoided for chemical process piping applications. Conversely, corrosion-resistant polyesters provide excellent value for various mildly corrosive processes. Vinyl ester resins offer enhanced corrosion resistance against strong oxidizing agents along with superior mechanical strength and temperature resistance compared to polyesters. Comprehensive corrosion resistance details are available for these resins.

Furan, phenolic, and epoxy resins tend to provide additional resistance to solvents and temperature, albeit occasionally at the expense of resistance to strong oxidizers. Corrosion-related information on these resins is often limited compared to polyester and vinyl esters, but significant improvements can be realized, particularly for transporting organics in acidic environments. Recommended practices for resin catalysts and post-curing should align with the resin manufacturer's guidelines for all previously mentioned resin types.

Corrosion Liner Construction:

The corrosion liner describes the internal section of the pipe laminate, comprising resin reinforced by a corrosion veil or veils, along with chopped strand fiberglass mat. The veil(s) may consist of either corrosion-grade fiberglass (C-glass), or an organic veil such as polyester (Nexus), ECTFE (Halar), or graphite. An organic veil is typically employed in environments known to degrade glass, such as sodium hydroxide and hydrofluoric acid.

Upon curing, the veil's thickness will range from 0.010 to 0.027, with 10% to 50% reinforcement for C-glass or Halar, respectively, and polyester falling in-between. The backing fiberglass chopped strand E-glass mat forming the remainder of the corrosion liner typically cures at a reinforcement level of approximately 30% +/- reinforcement. The final corrosion liner thickness may vary from as minimal as 0.040 for a C-veil with one layer of 1.5oz/ft2 chopped strand mat to over 0.250, contingent upon the customer's understanding of the corrosive properties of the contained fluid. The standard (SPI) corrosion liner is 0.100, while many pulp and bleach manufacturers routinely utilize liners twice that thickness.

It is crucial that the specifications clearly enumerate the corrosion liner and the allowance to avoid ambiguity. Some specifications permit the corrosion liner to count towards the required overall pipe wall thickness; others treat the liner as a sacrificial corrosion allowance without considering it in any structural calculations for pressure and vacuum handling capacity.

Temperature Requirements:

The thermal capabilities of various resin systems are contingent upon the corrosive nature of the process liquid. Generally, corrosion-grade isophthalic polyesters can withstand temperatures up to approximately 120-170F (50-75C), while vinyl esters can endure temperatures ranging from 170F-210F (75C-100C). Such temperature ranges are general guidelines; specific systems must be assessed in light of corrosion and, subsequently, mechanical requirements (supports, expansion, fatigue, etc.). Depending on the operational context, furan, phenolic, and epoxy resins may provide slightly elevated thermal thresholds.

Pressure & Vacuum:

Fiberglass pipe can be easily engineered to satisfy specific system pressure or vacuum requirements. It is standard practice to indicate pipe specifications in relation to the system's design pressure, typically in multiples of 25 PSIG (i.e., 25, 50, 75, 100, 125, or 150 PSIG designs). Increased pressure tolerances can be accommodated as necessary. When designing fiberglass pipe, a safety factor of 10 for internal pressure and a safety factor of 5 for vacuum is commonplace.

Abrasion Resistance:

To enhance abrasion resistance when needed, additives like ceramic fillers can be integrated into the fiberglass pipe corrosion liner. These configurations have been employed effectively in power plants and other demanding environments for many years. In addition to using fillers, additional layers or variations of veils may be considered.

Mechanical Design

Structural Design Principles:

Due to the diverse range of standards, there is no singular approach to designing fiberglass pipes. The following equations and constants may be employed in the mechanical design of such pipes, with acceptance criteria grounded in the latest ASTM D- (Standard Specification for Filament Wound Reinforced Thermosetting Resin Pipe):

Poisson Ratio:

The ratio of axial strain to hoop strain is generally reported as 0.30 for the laminates under consideration.

Density:

0.055 lb/in , or 1.5 gm/cm .

Specific Gravity: 1.5

Friction Coefficient:  Surface Roughness: 150-160 (Hazen-Williams)

Surface Roughness: 1.7 x 10 ft (Darcy-Weisbach/Moody)

Internal Pressure Rating:

Established on the hydraulic design principle for static or cyclic circumstances in accordance with ASTM D-. The design foundation is the hoop stress or strain aimed to provide an estimated life of 100,000 hours or 150 million cycles for static or cyclic conditions, respectively. Service factors typically range from 0.8 - 1.0 for cyclic scenarios and 0.50 - 0.56 for static conditions.

Thermal Conductivity:

• 1.0- 1.5 BTU/(ft )(hr)(°F)/inch for polyester / vinyl ester pipe. The equivalent K factor is 0.083 to 0.125 BTU/(ft )(hr)(°F).

Thermal Expansion:

The expansion in both the hoop and axial directions might vary. The typical axial expansion for filament-wound piping at a 55-degree wind angle-5 is 1.1 - 1.5 x 10 inches/inch/°F (approximately double that of steel).

Thermal expansion management in piping systems can be achieved through guides, expansion loops, mechanical expansion joints, anchors, or various combinations. These tools are utilized in a manner analogous to steel pipe design.

Fiberglass pipe possesses a significantly lower modulus compared to steel (<5% of steel). This characteristic greatly enhances the pipe's capacity to handle expansion and contraction stresses.

Several tables are available that define the design modulus needed for calculating this expansion/contraction force. Fiberglass-reinforced pipe is an anisotropic material resulting in various modulus values for tensile, bending, and compression measures, which again vary depending on the resin, reinforcement, and their orientation. Therefore, meticulous attention is warranted in ensuring that the correct modulus is applied, and a ply-by-ply laminate analysis is usually the most fitting approach. An example of such tables can be found in our Pipe Specifications.

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Supports and Guides:

Supporting fiberglass pipes is akin to supporting steel pipes, with several key considerations including:

• Avoiding point loading
• Providing sufficient support width with bearing stress < 85 psi.
• Employing abrasion shields for protection
• Supporting equipment and valves independently from the piping
• Avoiding unnecessary bending
• Minimizing load on vertical runs and alternatively supporting them in compression when feasible

Guides should be designed to permit axial movement only. Extra caution should be taken to safeguard contact points using a steel or fiberglass saddle affixed to the pipe. Anchors must be capable of securing the pipe against all acting forces. Anchors divide the piping system into various components that can then be evaluated for expansion needs. Equipment like pumps and valves can function as anchors, though additional ones may be necessary, with best practice suggesting their inclusion at least every 300 ft of straight run.

Guides and anchors operate as supports, which are essential to prevent excessive deflection of the pipe. Generally, a mid-span deflection of no more than 0.5 inches is acceptable as it avoids stressing the fiberglass pipe excessively. If the deflection exceeds this limit, a safety factor of 8:1 for bending stress is generally satisfactory.

Buried Pipe:

The design considerations for buried pipes exhibit notable differences from those for above-ground pipes. Most of these stipulations are encapsulated in Appendix A of AWWA Standard C-590-88. Additional design specifications will be necessary, covering factors such as pipe dimensions, surge pressure, working pressure, service temperature, soil conditions, soil-specific weight, cover depth, and traffic loads. It should be noted that while previous discussions used ASTM service design factors capped at 1.0, AWWA C-950 specifies design factors that are the inverse of service factors and are always greater than or equal to 1.0.

For specific advice in this domain, please contact Composites USA.

Joining Pipe:

Pipes from Composites USA can be connected through either butt and wrap (fiberglass lay-up) or flanged construction. Factory subassemblies are recommended for branch connections. The joining protocols for butt and wrap are equivalent to those outlined for Class 1 duct, also found in this catalog binder. The parameters for joint thickness and width will fluctuate based on the pressure classification and liner prerequisites of the system.

Cost Comparison:

Hydraulics:

Composites USA's fiberglass pipes provide significant hydraulic advantages over traditional steel pipes due to various reasons:

• Fiberglass pipes boast a smoother internal surface compared to steel
• Fiberglass pipes maintain their smooth surface better over time than steel
• Fiberglass pipes offer larger cross-sectional flow areas

The internal surface of fiberglass pipes surpasses that of steel pipes in smoothness, with Hazen-Williams roughness coefficients of 160 for new and 150 for used fiberglass. Conversely, steel pipes have a roughness coefficient of 120 for new and 65 for used. The substantial loss of smoothness in steel pipes is attributed to scale accumulation. It's essential to note that fiberglass pipes remain significantly smoother than new steel pipes.

Composites USA, along with numerous other fiberglass pipe manufacturers, maintains that their pipe and fittings have internal diameters aligning with nominal pipe sizes. For instance, an 18-inch fiberglass pipe would exhibit an 18-inch internal diameter, whereas an 18-inch schedule 40 steel pipe would show a 16.88-inch internal diameter, providing a mere 88% of the flow area compared to its fiberglass equivalent.

These critical distinctions directly correlate to substantial cost reductions achievable through the adoption of fiberglass piping, as presented below.

Material Costs:

The initial material purchase price for fiberglass pipes and fittings in standard installations has been reported at 0.75 to 2 times the cost of similarly sized stainless steel pipe systems. Nevertheless, this initial cost represents just one aspect of determining the overall system expenses. An analysis of both installation and operating costs typically advocates for the use of fiberglass piping systems.

Besides the material acquisition cost, the overall system expense evaluation should encompass the following:

Pipe Installation Costs

• Material purchase costs (advantage usually with stainless steel)
• Support specifications (supports, anchors, expansion joints - fiberglass reinforced plastic advantages)
• Joint assembly times (cutting and welding - advantage for fiberglass reinforced plastic)
• Rigging requirements (comparing lightweight fiberglass reinforced plastic vs. steel - advantage for fiberglass reinforced plastic)

Pipe Operating Costs

• Energy expenditures (pump horsepower needs - fiberglass reinforced plastic advantage)
• Maintenance obligations (painting, repairs, descaling, etc. - advantage for fiberglass reinforced plastic)

Total System Life Cycle Costs

• This sum aggregates the aforementioned costs over the anticipated lifespan of the system, employing discounted cash flow or analogous methodologies to allocate a time value to future cash flows (advantage fiberglass reinforced plastic).

Variations in pipe purchase cost differentials can be significant based on elements such as stainless steel prices and pipe specification standards. However, comparing prices is typically straightforward for the consumer. Other factors may be less transparent, and additional information provided below may assist.

The industry standard for connecting Composites USA's fiberglass pipes relies on flanged ends or butt and strap connections. Butt and strap is the preferred method for most extreme corrosion circumstances, involving the alignment of the fiberglass ends and executing a wet fiberglass lay-up (strap) over the joint area. Although skilled training is necessary to execute this procedure successfully, it is usually less complex to master than welding stainless steel.

For budgetary considerations, the time needed to cut, prepare, and weld the two materials is as follows (to follow):

Operating Costs:

One of the primary motivations for opting for fiberglass pipes over standard carbon steel systems is typically its reduced operational costs or horsepower requirements.

The previous section highlighted the increased flow area usually present with fiberglass pipes (typically a 12% increase, based on the given 18-inch diameter example). This factor, among others, substantially contributes to the lower pumping costs associated with fiberglass piping. Additionally, fiberglass pipes have a reduced coefficient of friction, measuring 25% lower in new installations, which doubles the improvement in aged systems.

This characteristic allows system designers to either downsize the line (using fiberglass) or benefit from lower operating costs. These cost reductions are frequently considerable, and estimates can be derived as follows:

In the 18-inch diameter pipe scenario discussed earlier, assuming a flow rate of 6,000 gpm across a 2,000 ft straight pipe system, expenses will be estimated solely for one year (specifically year #3). This process can be replicated for each year of the system's expected useful life. The Hazen-Williams relationships will be employed in the following calculations. Other formulas, including the Colebrook equation, may also be utilized and should yield similar results.

FRP and dual laminate piping and tank liners typically feature a smooth interior surface. This smoothness minimizes friction and prevents the accumulation of deposits or scaling, which can lead to improved flow efficiency and reduced maintenance needs.

In addition to these features, FRP is a non-conductive material, making it suitable for applications where electrical conductivity is a concern. Composite piping is also highly customizable. It can be tailored to meet specific project requirements, including diameter, length, and special features like insulation, fire resistance, and abrasion resistance.
Low thermal conductivity is another benefit of FRP. It is most desirable in applications where maintaining temperature control or insulation is essential.

Thanks to its inherent resistance to corrosion and its long-term durability, FRP piping typically requires minimal maintenance compared to RLCS, SS, and alloys, which require regular, scheduled cleaning and coating to maintain corrosion resistance. While the initial cost may be higher than some other materials, the long-term advantages of FRP and dual laminate piping, i.e., reduced maintenance, longer service life, and corrosion resistance, along with the total cost of ownership, can make it the better choice for your operation.

Ultimately, the suitability of FRP piping depends on the specific application and environmental conditions. Careful consideration of project requirements and constraints is essential. Proper design, installation, and maintenance practices are also crucial to realizing the full benefits of FRP and dual laminate piping.

For a more thorough comparison of dual laminate and lined steel, please take a look at our technical bulletin.

To learn more about our different lines of composite piping and tanks, see our Products Overview page.

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