Theory

Piping span from last support to direction change should preferably not exceed ¼ of the maximum permissible span for straight pipe of the same nominal size and material.

Formulas and requirements used in span calculations are obtained from Kellogg Handbook and are as follows. Note that the span is calculated based on deflection and stress and the shorter of the two is the maximum allowable span.

• The allowable span (L) in feet based on stress is obtained from the formula:

  

• The allowable span (L) in feet based on deflection is obtained from the formula:

  

Where:

• W: Total Unit Weight in pounds per foot. This is sum of:
• Pipe weight (based on non corroded thickness)
• Weight of water
• Weight of insulation
• I: Moment of Inertia in inches 4 based on corroded thickness of pipe
• Z: Section Modulus in inches 3 based on the corroded thickness of pipe
• S_h: Allowable hot stress in PSI
• E: Modulus of Elasticity in PSI
• d: Limit of deflection in inches