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How It Works
Plastic pipe pressure class depends on the hydrostatic design stress (HDS) and the standard dimension ratio (SDR or SIDR). Different formulas apply depending on whether the pipe is controlled by inside diameter, outside diameter, or the AWWA C900 standard. This calculator also covers short-term strength and short-term pressure rating equations.
Example Problem
A PVC pipe has HDS = 2,000 psi and SDR = 21. What is the pressure class (outside diameter controlled)?
- PC = 2 × HDS / (SDR − 1) = 2 × 2,000 / (21 − 1)
- PC = 4,000 / 20 = 200 psi
Frequently Asked Questions
What is SDR in plastic pipe?
Standard Dimension Ratio is the outside diameter divided by the wall thickness. Lower SDR means a thicker wall and higher pressure rating. Common SDRs include 11, 17, 21, and 26.
What is the difference between SIDR and SDR?
SIDR (Standard Inside Dimension Ratio) uses inside diameter; SDR uses outside diameter. Inside-diameter-controlled pipes maintain a consistent bore size, while outside-diameter-controlled pipes maintain a consistent external size for fittings.
What is AWWA C900?
AWWA C900 is the standard for PVC pressure pipe used in municipal water distribution. It adds a surge pressure allowance to the working pressure when calculating the required SDR.
Related Calculators
- Steel Pipe Design Calculator — Barlow's formula for steel pipe.
- Aluminum Pipe Design Calculator — pressure rating for aluminum pipe.
- Buried Plastic Pipe Calculator — wall crushing checks for buried plastic.
- Pipe Expansion Calculator — thermal expansion for restrained and unrestrained pipe.
- Pipe Flow Calculator — compute flow rate and velocity in pipe systems.
- Pressure Unit Converter — convert between psi, kPa, and bar for pipe ratings.
National Resources Conservation Service. National Engineering Handbook. 1995. USDA.