What Is GRE Pipe? Glass Reinforced Epoxy

Quick Answer

GRE (Glass Reinforced Epoxy) pipe is a composite pipe made from glass fiber reinforcement embedded in an epoxy resin matrix. It is corrosion-proof, lightweight (approximately 1/5 the weight of steel), and suitable for temperatures up to 130°C, making it a cost-effective alternative to corrosion-resistant alloy pipe and lined steel pipe in oil and gas facilities.

GRE pipe is manufactured by filament winding: continuous glass fibers are wound around a mandrel at controlled angles while being saturated with epoxy resin. The winding angle (typically 55 degrees for pressure pipe) determines the pipe’s axial and hoop strength. After curing in an oven, the mandrel is removed and the pipe is finished.

Key Properties

Property	GRE Pipe	Carbon Steel Pipe
Density	1.8-2.0 g/cm3	7.85 g/cm3
Weight (NPS 6, similar rating)	~5 kg/m	~28 kg/m
Corrosion resistance	Immune to electrochemical corrosion	Requires coating/lining
Max temperature	93-130°C (per resin system)	425°C+
Max pressure	Up to 240 bar (per design)	Per schedule/grade
Thermal conductivity	0.3 W/m-K (insulating)	50 W/m-K
Internal surface	Smooth (low friction, Hazen-Williams C=150)	Rough (C=100-120)
Design life	20-25 years (standard)	20-30 years (with corrosion allowance)
Fire resistance	Burns if exposed; fire-resistant grades available	Non-combustible

Size and Pressure Ranges

Diameter Range	Pressure Classes (bar)	Standard
NPS 1 to NPS 4	16 to 240	ISO 14692
NPS 6 to NPS 12	10 to 100	ISO 14692
NPS 14 to NPS 24	10 to 50	ISO 14692
NPS 28 to NPS 48	5 to 25	Manufacturer-specific

Higher pressures are available in smaller diameters. For large-diameter, low-pressure applications (NPS 24+), GRE competes with HDPE pipe.

Joining Methods

Method	Description	Application
Adhesive bonded (key-lock)	Taper-taper joint with epoxy adhesive	Standard for process piping
Adhesive bonded (butt-and-strap)	Butt joint with overwrap laminate	Large diameter, field repair
Threaded	Molded threads with O-ring seal	Small bore, instrument connections
Flanged	GRE flange adapter + steel backing ring	Connection to steel piping, equipment
Mechanical coupling	Proprietary clamp systems	Repair, temporary connections

The adhesive bonded joint is the most common method. It requires trained installers and controlled cure conditions (temperature above 15°C, no moisture on joint surfaces).

GRE vs. Other Non-Metallic Pipe

Feature	GRE	HDPE	PVC/CPVC
Max temperature	130°C	60°C	60°C / 93°C
Hydrocarbon resistance	Excellent	Poor	Poor
Pressure (NPS 6)	Up to 100 bar	Up to 16 bar	Up to 15 bar
UV resistance	Good	Poor	Poor
Cost (installed)	High	Low	Low
Oil & gas suitability	Excellent	Water only	Chemical only

Applications in Oil and Gas

• Produced water and water injection piping
• Firewater mains and deluge systems (fire-rated GRE)
• Seawater cooling systems on offshore platforms
• Chemical injection lines
• Oily drain and sewer systems
• Utility water and HVAC piping in corrosive environments
• Downhole tubing (specialized grades)

Pro Tip

GRE pipe design per ISO 14692 uses a qualification-based approach. The pipe manufacturer must demonstrate long-term strength through 10,000+ hour regression testing. The qualified pressure and temperature envelope is specific to each manufacturer and product family. Specifying “GRE pipe” generically without reference to a qualified product system is insufficient. The project specification should reference ISO 14692 and require the manufacturer’s qualification data, including the pressure-temperature envelope and long-term hydrostatic design basis (HDB).

Standards

Standard	Scope
ISO 14692	GRP/GRE piping for petroleum and natural gas industries
ASTM D2310	Classification of machine-made FRP pipe
ASTM D2996	Filament-wound FRP pipe
AWWA C950	GRP pressure pipe for water
API 15HR	High-pressure FRP line pipe

Read the full guide to pipe types