• Collapse Strength - API
       
Input Field(s)      
Minimum Yield Strength (Yp) psi
Nominal OD (OD) in
Nominal ID (ID) in
       
Output Field(s)      
Wall Thickness (t) in
D/t Ratio  
Yield Strength Collapse psi
Plastic Collapse psi
Transition Collapse psi
Elastic Collapse psi
 

  • Calculation Guide
  • Overview - Collapse Strength (API)
    • When the external pressure on the pipe exceeds the internal pressure, it is then subject to collapse. Collapse is primarily dependant on the Yield Strength of the Material and the slenderness ratio - D/t. Four seperate collpase regimes have been identified as per API 5C3.
  • Equation
    • Yield Strength Collapse (py)
      • py = 2 Yp [(D/t)-1)/(D/t)2]
      • D/t Range: D/t_1 >= [D/t] >= 0
    • Plastic Collapse (pc)
      • pc = Yp [A/(D/t)-B]-C
      • D/t Range: D/t_2 >= [D/t] > D/t_1
    • Transition Collapse (Pt)
      • pt = Yp [F/(D/t)-G]
      • D/t Range: D/t_3 >= [D/t] > D/t_2
    • Elastic Collapse (Pe)
      • pe = 46.95 10 6/(D/t) [(D/t)-1]2
      • D/t Range: D/t > D/t_3
    • ------------------------------------------------------------
    • Yp - Minimum Yield Strength (psi)
    • t - nominal wall thickness (in)
    • D, OD - nominal OD of pipe (in)
    • A = 2.8762+0.1067 10-5 Yp+0.2130 10-10 Yp2 -0.5313 10-16 Yp 3
    • B = 0.02623 + 0.50609 10 -6 Yp
    • C = - 465.93 + 0.03086 Yp - 0.10483 10-7 Sy 2 + 0.36989 10-13 Sy 3
    • F = 46.95 x 106 [(3 B/A)/(2+B/A)]3/(Yp [(3 B/A)/(2+B/A) - B/A] [1 - (3 B/A)/(2+B/A)]2)
    • G = F B/A
    • D/t_1 = [(A - 2)2+8 (B+C/Sy)]0.5+(A - 2)}/[2 (B+ C/Sy)]
    • D/t_2 = [Yp (A - F)]/[C+Yp (B - G)]
    • D/t_3 = (2+B/A)/(3 B/A)
  • Assumptions
    • No applied forces, Internal Pressure
    • Long Tubes - L/D >8
  • Reference
    • API Bulletin 5C3 (1985)
    • Petroleum Well Construction; Economides, Watters, Dunn-Norman
  • Unit Conversion Tool