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