Thermoplastics major drawback is low mechanical strength, relative to other materials, which limits their use in large structures such as scrubbers, tanks, and medium to high pressure systems.

Fiberglass FRP composites, on the other hand, have been used in fabricating larger chemical process equipment due to the excellent mechanical properties imparted by the fiberglass reinforcement. As an added bonus, many fiberglass reinforcement resins offer excellent corrosion resistance properties of their own, making them suitable for a wide range of acidic and basic applications.

Dual laminate FRP composites, with a thermoplastic inner liner and a fiberglass composite exterior, combine the best advantages of thermoplastic corrosion resistance with reinforced thermoset plastics mechanical performance. All of this is accomplished at less cost than high nickel alloys, with less weight, cutting down transportation and installation costs, while also offering abrasion resistance, electrical and to some extent thermal insulating properties compared to metallic alternatives.

Liner Materials:

Thermoplastic liner materials typically used in dual laminate construction include most grades used for manufacturing small plastic pipe and equipment, such as polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polypropylene (PP), and the fluoropolymer family: polyvinylidine fluoride (PVDF), ethylene chlorotrifluoroethylene (ECTFE), fluorinated ethylenepropylene (FEP), perfluoroalkoxy (PFA), ethylene-tetrafluoroethylene (ETFE) and others.

Liner materials are selected based upon an evaluation of corrosion requirements at the process temperature, with other considerations such as flame retardancy, mechanical properties and cost being factored in. See the tables for additional guidance in these areas.

PVC and CPVC are usually bonded directly to the FRP laminate using a bonding resin, while other thermoplastic liners are typically manufactured with an embedded fabric or fiberglass backing. This fabric backing provides a strong mechanical lock when overlaid with the fiberglass structural composite.

Table 1. Corrosion Resistance of Typical Thermoplastic Liner Materials

		PVC	CPVC	PP	PVDF	ECTFE	ETFE	FEP	PFA
HCL,<36%	°F	104	180	140	285	300	300	300	300
	°C	40	82	60	140	149	149	149	149
HCL,36%	°F	NR	73	63	285	300	300	300	300
	°C		23	20	140	149	149	149	149
Sulfuric Acid, 100%	°F	NR	NR	NR	NR	73	120	300	300
	°C					23	50	149	149
Sulfuric Acid, 98%	°F	NR	73	NR	150	250	300	300	300
	°C		23		65	120	149	149	149
Sulfuric Acid, 50%	°F	104	180	140	250	250	300	300	300
	°C	40	82	60	120	120	149	149	149
Nitric Acid, 70%	°F	NR	73	NR	121	121	75	300	300
	°C		23		50	50	25	149	149
Nitric Acid, 35%	°F	NR	73	63	121	212	150	300	300
	°C		23	20	50	100	65	300	300
Sodiulm Hydroxide, 50%	°F	140	180	212	NR	250	230	300	300
	°C	60	82	100		120	110	149	149
Sodiulm Hydroxide, 10%	°F	140	180	212	120	300	230	300	300
	°C	60	82	100	50	149	110	149	149
Sodium Hypochlorite, 12.5%	°F	104	180	63	200	250	300	300	300
	°C	40	82	20	95	120	149	149	149
Hydroflouric Acid, 70%	°F	NR	NR	NR	200	212	250	300	300
	°C				95	100	120	149	149
Hydroflouric Acid, 40%	°F	104	160	140	250	250	275	300	300
	°C	40	70	60	120	120	130	149	149

NR= Not Recomended  The information in this table has been provided by thermoplastic manufacturers

Engineering & Product Design:

Following the selection of an appropriate liner material, the overall product design is completed by an evaluation of equipment mechanical requirements based upon pressure, vacuum, wind, seismic and any other mechanical loads. The fiberglass structure itself is designed using well established guidelines from such sources as the ASME RTP-1 (U.S.A.), BS-4994 (U.K.), CGSB-41.22-93 (Canada) or others. Many of these same standards also provide guidelines for proper application of dual laminate fabrication techniques.

These international standards take into account the anisotropic nature of fiberglass reinforced laminates, which results in behavior much different than typical steel alloys. Composites USA has been designing and building RTP composite equipment since 1982, and we have a thorough understanding of how these materials behave.

With our experienced composites engineers and extensive proprietary computer analysis tools, we are able to design the most cost effective long term solution to your process equipment needs. Where required for insurance or other reasons, calculations and drawings can be stamped by Composites USA licensed PE's.