To make thermoplastics practical for pipe installations, they were adopted, early on, as lining materials for traditional and relatively inexpensive steel pipe. The liner protected the steel from the corrosive effects of chemicals while the steel provided the structural strength and stiffness to support the thermoplastic. This solution, however, was not without its problems. Tensile and flexural modulus are low for most thermoplastics and, because thermoplastics creep, these properties diminish over time as the material is exposed to operating stress. If a thermoplastic liner cannot be adequately bonded to the exterior pipe material, such as steel, then creep and high thermal contraction/expansion can lead to mechanical failure of the lining. In addition, the steel exterior is still vulnerable to corrosion and is also heavy, increasing shipping and handling costs.

Conventional anticorrosive alternatives – stainless steel and titanium – have sufficient strength and are effective against corrosion, but are much more expensive. Stainless steel (a steel/chromium alloy) was, in fact, invented for corrosion-resistant applications. Its chromium content (from 10 to 26 percent) is reactive, and forms a passivation layer – a thin film – of chromium oxide (Cr2O3), which is highly resistance to acidic corrosion. It is not immune to corrosion, however, when exposed to strong acids. For that reason, stainless steel pipe designers rely on known data to determine the steel’s required chromium content, predict a particular pipe’s useful life and establish replacement dates. Titanium, with 60 percent less density than steel (hence, less weight), forms a more effective oxide film, but is still susceptible to pitting and general erosion when exposed to organic chlorides, wet chlorine and/or seawater at elevated temperatures.

When isophthalic polyester thermosetting resins were developed (circa. 1960), their anticorrosive properties (contributed by the oxidizing properties of isophthalic acid) fueled the introduction of fiberglass composites in the anticorrosion market. In particular, they replaced rust-prone steel in underground gasoline storage tanks. Today, a wide range of products, from piping to cooling towers, are manufactured from glass fiber-reinforced isopolyesters and epoxy vinyl esters, which are resistant to both acidic and alkali environments.

Winning a Place in the Market

Against that backdrop, dual-laminate technology was developed. CPF Dualam Inc. (Montreal, Canada) was the first to use this technology, in 1957. In the last 40 years, the company has played a leading role in making dual laminate products available in industrial processes that require the handling of highly corrosive materials. In 2002, CPF Dualam merged with Prolite Plastics (Port Coquitlam, British Columbia, Canada), which was renamed CPF Dualam Vancouver. The move combined CPF Dualam’s expertise in the dual-laminated pressure vessel market with Prolite’s knowledge of dual-laminate pipe manufacturing.

Dual laminate refers to a method of construction that permits a pipe fabricator to combine a thermoplastic liner material with a fiber-reinforced thermoset composite to make a structure with high strength-to-weight but broader corrosion resistance, less tendency to crack during handling and installation and greater resistance to brittle fracture at low temperatures than FRP alone. Although dual laminates historically have required a more costly manufacturing process than fiberglass, Guyle McCuaig, vice president of CPF Dualam Vancouver maintains that the premium price is justified by the lengthier service life and reduced maintenance cost. Further, the liner effectively isolates the pipe’s fiber reinforcement from potential contact with corrosive chemicals.

“We are competing with titanium and stainless steel in the critical service industry for severe corrosion,” says McCuaig, noting that dual-laminate pipe is lighter than comparable titanium pipe and comes in at about half the cost. Unlike lined steel, dual laminates will not externally corrode and, according to the company’s calculations, weigh 75 percent less.

The company can custom fabricate pipe (to 48 inch/122 cm diameter), cylindrical tanks and self-supporting stacks and cooling towers, using liners made from polyvinyl chloride (PVC), polypropylene (PP), chlorinated polyvinyl chloride (CPVC), polyvinylidene fluoride (PVDF), ethylene chlorotrifluoroethlyene (ECTFE) and perfluoroalkoxy (PFA). The resulting products can replace more expensive metal alloys, lined steel and unlined FRP in many high-risk applications, including chlor-akali (tanks, cooling towers) pulp bleach plants (tanks, ClO2 generators), environment protection (gas scrubbers) and containment and piping systems for chemicals used in metal refining and fertilizer manufacturing.

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