In short: An FRP pipe pressure rating comes from long-term pressure tests, extrapolated to a design life and reduced by a design factor set by the standard. For water, AWWA C950 covers fiberglass pressure pipe in classes from 50 to 450 psig. ASTM D2996 covers filament-wound industrial pipe, ASTM D2992 is the test practice behind the long-term rating, and ISO 14692 covers GRP piping for oil and gas. Name one standard, give the operating, design and surge pressures, and check that joints and fittings carry the same rating as the pipe.
FRP (GRP, fiberglass) pipe is used for water, wastewater, cooling water, seawater and chemical lines. Unlike steel pipe, its strength depends on time under load. A short burst test says little about how the pipe will behave after decades at pressure, so the standards rate FRP pipe from long-term data. For the basics of FRP pipe, see FRP pipe basics.
How a pressure rating is set
ASTM D2992 is the standard practice for obtaining a hydrostatic design basis (HDB) or pressure design basis for fiberglass pipe and fittings. Pipe samples are held at a range of pressures until they fail, and the results are plotted on a log-log regression. The line is extrapolated to the design life; the long-term value is then reduced by a design (service) factor given in the product standard or design code. The result is the pressure class or rated pressure printed on the pipe.
Two points follow. First, the rating is only valid for the temperature and fluid it was tested for; at higher temperature, the supplier must show data or a derating. Second, the weakest part of a line is often a joint or fitting, not the pipe. Check that every fitting and joint type has a rating at least equal to the system design pressure.
The main standards
AWWA C950: fiberglass pressure pipe for water
AWWA C950-20 covers fiberglass pressure pipe for water supply, from 1 in to 156 in in diameter, in pressure classes from 50 to 450 psig. It is commonly named for potable water, raw water and treated effluent lines in North America and beyond. A revised edition was published in 2025; confirm which edition your project names.
ASTM D2996: filament-wound industrial pipe
ASTM D2996 covers filament-wound fiberglass pipe and classifies it by properties including its long-term hydrostatic strength. It is often named for industrial and chemical process piping.
ISO 14692: GRP piping for oil and gas
ISO 14692 (Parts 1 to 4) covers GRP piping in the petroleum and natural gas industries: vocabulary and applications, qualification and manufacture, system design, and fabrication, installation and operation. It is common on offshore platforms and in refineries.
Marine piping
On ships, plastic piping is governed by IMO Resolution A.753(18) as amended, which sets fire endurance levels for plastic pipes by location and service. Class society approval is often requested; see our guide to what marine buyers ask for in approvals.
Key parameters at a glance
| Standard | Scope | Pressure basis | Typical use |
|---|---|---|---|
| AWWA C950-20 | Fiberglass pressure pipe, 1–156 in | Classes 50–450 psig | Water and wastewater |
| ASTM D2996 | Filament-wound pipe | Long-term hydrostatic strength class | Industrial and chemical |
| ASTM D2992 | Test practice | Hydrostatic / pressure design basis | Behind ratings in other standards |
| ISO 14692 | GRP piping, oil and gas | Qualified and design pressure | Offshore, refineries |
| IMO A.753(18) | Plastic pipes on ships | Fire endurance by location | Marine |
Pressure terms to give the supplier
- Operating pressure: the normal working pressure.
- Design pressure: the highest sustained pressure the line must carry.
- Surge pressure: water hammer from pump trips and valve closure. Ask how the standard treats surge for the pipe offered.
- Vacuum: buried and large-diameter pipe must also resist external pressure and vacuum; stiffness class matters.
- Test pressure: the site hydrotest, from the project specification.
Joints and fittings
Common joints are butt-and-strap (butt-wrap), bell and spigot (adhesive or with elastomeric seals), and flanges. Each has its own pressure capability and installation needs. See FRP pipe joints. Flanges must match the bolt pattern of the mating equipment; state the flange standard.
Temperature and chemicals
The resin decides both chemical resistance and the temperature limit. Give the fluid, concentration and the maximum temperature, including upset conditions. See FRP temperature limits by resin type. For a comparison with other materials, see FRP vs HDPE vs steel pipe.
What to send for a quote
Send the fluid and temperature, operating, design, surge and vacuum pressures, diameters and lengths, preferred joint type and flange standard, the standard to follow, and whether the line is buried or above ground with support spacing.
Ready to quote? FIBROVX manufactures FRP products in our own factory in China and builds every item to order: sizes, resin system, color, molds and OEM branding. Send drawings, cut lists and duty data to FIBROVX. Trade terms default to CIF destination port; FOB China port is available on request.
Catalog pipe range
- Sand-filled pipe (RPMP): DN300–2800
- Pressure classes: 0.6 / 1.0 / 1.6 MPa
- Stiffness classes: SN2500 / SN5000 / SN10000 (selected independently of pressure)
- Matching elbows, tees and reducers and flanges
See FRP piping systems and fitting and flange dimensions.
Watch: Pressure & Stiffness in 27 Seconds
FAQ
What pressure classes does AWWA C950 cover?
AWWA C950-20 covers fiberglass pressure pipe from 1 to 156 in in classes from 50 to 450 psig.
What is ASTM D2992?
It is the standard practice for obtaining the hydrostatic or pressure design basis of fiberglass pipe and fittings from long-term pressure tests.
Which standard is used for offshore GRP piping?
ISO 14692 is the common standard for GRP piping in the petroleum and natural gas industries.
Are fittings rated the same as the pipe?
Not always. Check that every fitting and joint is rated at least to the system design pressure.
Does temperature affect the pressure rating?
Yes. Ratings apply to the tested temperature; ask for data or a derating at higher temperatures.
Related guides
Sources
- AWWA C950-20, Fiberglass Pressure Pipe, https://store.awwa.org/AWWA-C950-20-Fiberglass-Pressure-Pipe
- ASTM D2992-18, Obtaining Hydrostatic or Pressure Design Basis for "Fiberglass" Pipe and Fittings, https://store.astm.org/d2992-18.html
- ASTM D2996-17, Filament-Wound "Fiberglass" Reinforced Thermosetting-Resin Pipe, https://store.astm.org/d2996-17.html
- ISO 14692 (Parts 1–4), Petroleum and natural gas industries — Glass-reinforced plastics (GRP) piping, https://www.iso.org
- IMO Resolution A.753(18), Guidelines for the application of plastic pipes on ships (as amended)
- International Chamber of Commerce, Incoterms® 2020 rules, https://iccwbo.org/business-solutions/incoterms-rules/incoterms-2020/