255.121 - Design of plastic pipe

(a) Design pressure.

Design pressure. Design pressure plastic pipe is determined in accordance with either of the following formulas

Where:

P = Design pressure, gauge, psig (kPa).

S = For thermoplastic pipe, the hydrostatic design basis (HDB) is determined in accordance with the listed specification at a temperature equal to 73°F (23°C), 100°F (38°C), 120°F (49°C), or 140°F (60°C). In the absence of an HDB established at the specified temperature, the HDB of a higher temperature may be used in determining a design pressure rating at the specified temperature by arithmetic interpolation using the procedure in Part D.2 of PPI TR-3/2012, (incorporated by reference, see § 255.7 of this Part).

For reinforced thermosetting plastic pipe, 11,000 psig (75,842 kPa).

t = Specified wall thickness, inches (mm).

D = Specified outside diameter, inches (mm).

SDR = Standard dimension ratio, the ratio of the average specified outside diameter to the minimum specified wall thickness, corresponding to a value from a common numbering system that was derived from the American National Standards Institute (ANSI) preferred number series 10.

DF = Design Factor, a maximum of 0.32 unless otherwise specified for a particular material in this section .

(b)  General requirements for plastic pipe and components.

(1)  Except as provided in subdivisions (c) through (f) of this section, the design pressure for plastic pipe may not exceed a gauge pressure of 100 psig (689 kPa) for pipe usedin:

(i)  Distribution systems; or

(ii)  Transmission lines in Class 3 and 4 locations.

(2)  Plastic pipe may not be used where operating temperatures of the pipe will be:

(i)  Below -20°F (-29°C), or below -40°F (-40°C) if all pipe and pipeline components whose operating temperature will be below -20°F (-29°C) have a temperature rating by the manufacturer consistent with that operating temperature; or

(ii)  Above the temperature at which the HDB used in the design formula under this section is determined.

(3)  Unless specified for a particular material in this section, the wall thickness of plastic pipe may not be less than 0.062 inches (1.57 millimeters).

(4)  All plastic pipe must have a listed HDB in accordance with PPI TR-4/2012 (incorporated by reference, see § 255.7 of this Part).

(c)  Polyethylene (PE) pipe requirements.

(1)  For PE pipe produced after July 14, 2004, but before January 22, 2019, a design pressure of up to 125 psig maybe used, provided:

(i)  The material designation code is PE2406 or PE 3408.

(ii)  The pipe has a nominal size (Iron Pipe Size (IPS) or Copper Tubing Size (CTS)) of 12 inches or less (above nominal pipe size of 12 inches, the design pressure is limited to 100 psig); and

(iii)  The wall thickness is not less than 0.062 inches (1.57 millimeters).

(2)  For PE pipe produced on or after January 22, 2019, a DF of 0.40 may be used in the design formula, provided:

(i)  The design pressure does not exceed 125 psig;

(ii)  The material designation code is PE2708 or PE4710;

(iii)  The pipe has a nominal size (IPS or CTS) of 24 inches or less; and

(iv)  The wall thickness for a given outside diameter is not less than that listed in the following table:

(d)  Polyamide (PA-11) pipe requirements.

(1)  For PA-11 pipe produced after January 23, 2009, but before January 22, 2019, a DF of 0.40 may be used in the design formula, provided:

(i)  The design pressure does not exceed 200 psig;

(ii)  The material designation code is PA32312 or PA32316;

(iii)  The pipe has a nominal size (IPS or CTS) of 4 inches or less; and

(iv)  The pipe has a standard dimension ratio of SDR-11 or less (i.e., thicker wall pipe).

(2)  For PA-11 pipe produced on or after January 22, 2019, a DF of 0.40 may be used in the design formula, provided:

(i)  The design pressure does not exceed 250 psig;

(ii) The material designation code is PA32316;

(iii)  The pipe has a nominal size (IPS or CTS) of 6 inches or less; and

(iv)  The minimum wall thickness for a given outside diameter is not less than that listed in the following table:

(e)  Polyamide (PA-12) pipe requirements.

For PA-12 pipe produced after January 22, 2019, a DF of 0.40 may be used in the design formula, provided:

(1)  The design pressure does not exceed 250 psig; (2) The material designation code is PA42316;

(3)  The pipe has a nominal size (IPS or CTS) of 6 inches or less; and

(4)  The minimum wall thickness for a given outside diameter is not less than that listed in the following table.

(f)  Reinforced thermosetting plastic pipe requirements.

(1)  Reinforced thermosetting plastic pipe may not be used at operating temperatures above 150°F (66°C).

(2)  The wall thickness for reinforced thermosetting plastic pipe may not be less than that listed in the following table: