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TRANSCRIPT
Study of Stress on
Pipeline Crossing of Oil
India Pipeline
G. Sarvesh
Sr. Engg (PLM)
Oil India Limited
Brief Overview
❖Oil India Limited operating 1157 Km of cross
country crude oil pipeline and 652 Km of Multi
product pipeline.
❖ There are total of 226 road cased crossings and 64
railroad cased crossings along the crude oil
pipeline.
❖ There are total of 138 road crossings and 30
railroad cased crossings along the multi product
pipeline.
❖Due to various developmental activities
around RoW, new roadways and railroads
are being constructed or widened crossing
across RoW.
❖Safety assessment of pipeline need to be
carried out taking into account of all the
applicable stresses and necessary
arrangements shall be made for protection
of the pipeline.
● Details of Crude Oil Pipeline.
○ Grade – API 5L x 46
○ Nominal wall thickness – 7.92 mm
○ Crossings wall thickness – 11.95 mm
○ Pipe Diameter – 14” & 16”
○ MAOP – 101 Kg/cm2 & 86 Kg/cm2
● Details of Multi Product Pipeline.
○ Grade – API 5L x 46, 52, 60
○ Nominal wall thickness – 7.9 mm, 6.4 mm
○ Crossings wall thickness – 11.9 mm
○ Pipe Diameter – 16”
○ MAOP – 84.5 Kg/cm2
● Assuming a 14” crude oil pipeline needs to
be protected against proposed roadway
(National Highway) construction.
○ Nominal wall thickness - 7.92 mm
○ Grade - x46 (317 Mpa)
○ Depth of pipe from Road level – 2 m
○ MAOP – 101 Kg/cm2
○ Design Factor – 0.72
❖Allowable stress value (Saw)= F * E * SMYS
= 228 Mpa
❖Barlow Stress, S(Hb) = P * D / (2 * t)
=
222.35
❖Check whether S(Hb) < (Saw)
YES
❖ Circumferential stress due to Earth load,
S(He) = K(He) * Be * Ee * γ * D
= 19.34 Mpa
• K(He) – Stiffness Factor for circumferential stress
from earth load
• Be - Burial Factor for Earth load
• Ee - Excavation Factor for Earth load
• γ - Soil unit weight.
• D - Outside diameter of the Pipe
❖ Impact Factor is the factor at which live load gets
increased (Fi)
= 1.48
❖ Cyclic Circumferential Stress, ΔSHh
= K(HHh) * G(HHh) * R * L * Fi * w
=13.47 Mpa
• K(HHh) - Highway stiffness factor for cyclic
circumferential stress
• G(HHh) - Highway geometry factor for cyclic
circumferential stress
• R - Highway pavement type factor
• L - Highway axle configuration factor
• Fi - Impact factor
• w - Applied Design Surface Pressure
Cyclic Stresses
❖ Cyclic Longitudinal Stress , ΔSLh
= K(HLh) * G(HLh) * R * L * Fi * w
=10.28 Mpa
• K(HLh) - Highway stiffness factor for cyclic
longitudinal stress
• G(HLh) - Highway geometry factor for cyclic
longitudinal stress
• R - Highway pavement type factor
• L - Highway axle configuration factor
• Fi - Impact factor
• w - Applied Design Surface Pressure
❖ Circumferential Stress due to internal Pressure,
S(Hi) = P * (D-t) / 2t
= 217.4 Mpa
❖ Principal Stresses S1, S2, S3
● Maximum Circumferential Stress, S1
= S(He) + ΔSHh + S(Hi)
= 250.21 Mpa
• Maximum Longitudinal Stress, S2
= ΔSHh – Es * αT * (T2 – T1) + νs*(S(He) + S(Hi))
= 81.3 Mpa
• Maximum Radial Stress, S3
= - P
= - 9.90 Mpa
❖Total Effective Stress,
Seff = Sqrt(1/2((S1-S2)
2 +(S2-S3)2 +(S3-S1)
2 ))
= 228.6 Mpa
❖Check whether Seff < Saw
NO
❖ The stress can be brought within the allowable
stress value by various ways.
❖ Some of the ways it can be achieved are by
increasing the pipe grade, pipe wall thickness,
increasing the depth of the pipe etc.
❖ There are limitations in case of already installed
and operating pipelines.
❖ The same can be achieved by increasing the
allowable stress value of the pipeline above the
total effective stress at that section
❖ Structural strengthening in localized areas can
be carried out for achieving higher allowable
stress value.
❖ Strengthening can be done by application of
composite fibre reinforcement .
❖Reinforcing the pipe may increase the strength
or allowable stress value upto 20%.
❖Hence after application of reinforcement,
allowable stress value of the localized section
shall be
Saw = 228 Mpa + 20% of 228 Mpa
= 273.6 Mpa
❖ Total effective Stress, Seff = 228.6 Mpa
❖ Check whether Seff < Saw YES
❖
❖For National Highway and Railroad crossings,
Casing Pipes are installed over the carrier pipe
for maintainability of the pipeline at crossings.
❖Composite Fibre Reinforcement over the
carrier pipe at such places shall act as
additional mitigation measure by providing
additional strength to the pipe and also
providing corrosion allowance to the pipe.
❖Minimum casing wall thickness at crossing
as per API 1102 are,
For 14” Nominal Pipe Diameter
Railroad crossing = 4.78 mm
Highway crossing = 3.40 mm
❖Split casing pipes are used at OIL Pipeline
crossings of diameter 6 mm and confirming
to IS 2062.
Thank You