When pipes are installed by HDD, they often experience high tension loads, severe bending, and external fluid pressures. Often these installation loads are more severe than the design service loads. When selecting the appropriate pipe materials for an HDD installation, the designer must consider the pipe properties as well as the borehole profile. These two factors should be considered together in order to choose the best material and profile so that the pipeline can be installed and operated without risk of damage. To ensure that the material and bore-hole profile are suitable for the proposed application, the installation, operational, and combined loads and stresses are analyzed.
πππππ€πππβπ‘Β = 10.68 (π· β π‘)π‘
πππππ€πππβπ‘ β Weight of the pipe (lbs/ft)
D – Pipe Outside Diameter (inch)
t – Pipe Wall Thickness (inch)
(to be calculated only if the pipe is filled with water)
πππ‘πππβ’π€πππβπ‘Β = πππππππ‘πππππΒ β’Β π£ππΒ β ππ€πππβπ‘
Wweight β Weight of water (lb/ft3)
π·ππ πππππππ’πππππβπ‘Β = ππππππ₯π‘β’π£ππππ’ππ€π‘
mudwt = Weight of mud (lb/gal)
Effective Weight of Pipe:
ππΒ =Β πππππ€πππβπ‘Β +Β πππ‘πππβ’π€πππβπ‘Β βΒ π·ππ πππππππ’πππππβπ‘
Friction from Soil:
ππππ2Β =Β πππΏ1πππ ππ1πππππ
πΏ1 β Length of the straight section 1
ππ1 – Angle in degrees from horizontal for straight section 1
πππππ – Average coefficient of friction between pipe and soil. The recommended value is between .21-.3 (Maidla)
Drag Forces from Mud:
π·πππ2Β = ππ·πΏ1πππ’π
ΞΌmud – Fluid drag coefficient for steel tube pulled through bentonite mud
Tension on Section:
βπ2Β = |ππππ2| + π·πππ2Β β ππ πΏ1π ππππ 1
Cumulative Pull Load:
π2Β = βπ2Β + π1
T1 – Pull back as the pipe enters the drill hole (lbf)
(based on Roarkβs solution for elastic beam deflection)
ΞΈC1Β – Angle in degrees from horizontal for curved section 1
R1Β – Radius of curvature of curve section 1 (ft)
Larc1Β – Length of curved section 1(ft)
E – Young’s Modulus (psi)
Friction from Soil:
ππππ = |π3πππππ|
Drag Forces from Mud:
π·πππ3Β = ππ·πΏπππ1πππ’π
Tension on Section:
Cumulative Pull Load:
π3Β = βπ3Β + π2
Friction from Soil:
ππππ4Β = πππΏπ πππ πππππππ
LsΒ – Length of straight section between bends (ft)
ΞΈsΒ – – Angle in degrees from horizontal for straight section between bends
Drag Forces from Mud:
π·πππ4Β = ππ·πΏπ πππ’π
Tension on Section:
βπ4Β = |ππππ4| + π·πππ4Β β ππ πΏπ π ππππ
Cumulative Pull Load:
π2Β = βπ4Β + 3
ΞΈC2Β – Angle in degrees from horizontal for curved section 2
R2Β – Radius of curvature of curve section 2 (ft)
Larc2Β – Length of curved section 2(ft)
Friction from Soil:
ππππ = |π3πππππ|
Drag Forces from Mud:
π·πππ3Β = ππ·πΏπππ2πππ’π
Tension on Section:
Cumulative Pull Load:
π3 = βπ3 + π2
Friction from Soil:
ππππ6Β = πππΏ2πππ ππ2πππππ
Drag Forces from Mud:
π·πππ6Β = ππ·πΏ2πππ’π
Tension on Section:
βπ6Β = |ππππ6| + π·πππ6Β + ππ πΏ1π ππππ 12Β β Length of the straight section 2
ΞΈS2Β –Β Angle in degrees from horizontal for straight section 2
Cumulative Pull Load:
π6Β = βπ6Β + π5
Total pull load of the pipe:
ππ‘ππ‘ππΒ = βπ2Β + βπ3Β + βπ4Β + βπ5Β + βπ6
TtotalΒ – Total pull load of the pipe (lbf)
Maximum Pull Force, F:
ID β Internal Pipe Diameter (inch)
fs β Safety Factor
F – Maximum pull force (lbf)
Tensile Stress at a Point:
Allowable Tensile Stress:
πππ‘πππ π β’πππππ€Β = 0.9ππππ
Bending Stress at a point:
Allowable Bending Stress:
Hoop Stress at a point:
Allowable Hoop Stress:
Unity Check β Tensile and Bending Stress:
Β
Unity Check β Tensile, Bending & Hoop Stress:
*The design changes based on borehole design (section configuration)
Β
Select Point of Interest (B)
Select Point of Interest (C)
Select Point of Interest (D)
Select Point of Interest (E)
Select Point of Interest (F)
Β