MRS
Minimum Required Strength
MRS is the extrapolated stress at 200oC and 50 years obtained by long term hydrostatic tests and differs for each plastics material.
C
Safety Factor
It differs depending on the service (water, gas, etc), temperature and plastics type (PVC, HDPE etc)
Design Stress
The basic parameter that is used for all calculations (wall thickness, pressure class etc.) and it is calculated upon the values of MRS and C.
e: wall thickness (mm.)
The two formulas above are the basic formulas to calculate the dimensions and the wall thickness of a pipe for a given pressure and diameter value.
MRS, C (for water service) and values are shown in the table below for pressurized pipes manufactured from different resins.
SDR
Standard Dimensions Ratio
The parameter that is used for the definition of pipes. It is the ratio of outer diameter to wall thickness.
S
Pipe Series
Another parameter that is used for the definition of pipes. It is the ratio of design stress to pressure class.
PN
Nominal Pressure
This is the parameter that shows the working pressure of the system, it is also defined in water services as "Maximum Permissible Operating Pressure".
In the table below, the pressure classification of different classes of PE Pipes is shown according to their SDR and S values.
