Underground pipe design

UNCASED DESIGN - Highway Crossing Pipeline (Ref : API RP 1102 - Steel Pipeline Crossing Railroads and Highways) Step - a - Intial Design Information Pipe and Operational Characterists :  Outside Dia Operating pressure Steel Grade Specified Min yield Strength Design factor Longitudinal joint factor Installation Tempreture Max. or Min. operating Temp. Temp. derating factor W all Thickness

D p

24 300 X52 52000 0.72 1 N/A N/A N/A 0.375

SMYS F E T1 T2 T tw

inch psig p si

in

Installation & site Characterists :  Depth Bored Dia. Soil type Modulus of soil reaction Resilient Modulus Unit W eight Type of longitudinal weld Design wheel load - Signle Axle Design wheel load - tandem Axle Pavement Type

H Bd E' Er uw Ps Pt

3.28 28 Loose Sand 0.5 10 120 ERW 12 10 Flexible

ft in k si k si lb/ft3 kips kips

Other pipe steel properties :  Young's modulus Poisson's ratio Coefficient of thermal expansion

Es vs at

30000 0.3 6.50E-06

300 24 0.375 0.72 1 0 52000

psig in in

ks i per deg F

Step - b - Check Allowable Barlow Stress Equation 8b with :

p D tw F E T SMYS

<

SHi (Barlow)

Shi (Barlow)= pxD/(2tw)

9600 psi

For Natural Gas: FxExTxSMYS = For liquid & other products: FxExSMYS =

p si

FxExSMYS

OK Step - c - Circumferential Stress Due to Earth Load c.1 Figure 3 with :

tw / D E'

c.2 Figure 4 with :

H / Bd Soil Soil Type Type

c.3 Figure 5 with :

Bd / D

c.4 Equation 1 with :

D uw

0.0156 0.5 ksi

KHe

3250

1.4057143 Loos Loose e San Sand d

Be

0.4

1.167

Ee

1.08

24 in 120 lb/ft3 0.0694444 lb/in3

SHe = Khe x Be x Ee x uw x D 2340 psi

Step - d - Impact Factor, Fi, and and Applied Design Surface Pressure, w d.1 Figure 7 for highway with : d.2  Applied Design Design Surface Pressure, w Section 4.7.2.2.1 :

H

Flexible

3.28

Fi

Pt w

1.5

12 kips 83.3 psi

0 3744 37440 0 psi psi

Step - e - Cyclic Stresses, DSHh & DSLh e.1 Cyclic circumferential stress DSHh e.1.1 Figure 14 with :

e.1.2 Figure 15 with :

e.1.3 Table 2 with : Flexible Pavement Tandem Axles

tw / D Er

0.015625 10 ksi

e.2.2 Figure 17 with :

e.2.3 Table 2 with : Flexible Pavement Tandem Axles

13

1.15

D H

24 in 3.28 ft

GHh

H D

3.28 ft 24 in

R L

1 1

DSHh = KHh x GHh x R x L x Fi x w 1868.0025 psi

e.1.4 Equation 5 with :

e.2 Cyclic Longitudinal stress DSLh e.2.1 Figure 16 with :

KHh

tw / D Er

0.015625 10 ksi

KLh

10

D H

24 in 3.28 ft

GLh

1

H D

3.28 ft 24 in

R L

1 1

DSLh = KLh x GLh x R x L x Fi x w 1249.5 psi

e.2.4 Equation 6 with :

Step - f - Cercumferential Stress Due to Internal Pressurization, Shi Equation 7 with :

p D tw

300 psi 24 in 0.375 in

SHi = p x (D-tw) / (2 x tw) 9450.000 psi

Step - g - Principal Stresses S1 , S2 , S3 Es at T1 T2 vs

30000 6.50E-06 0 0 0.3

g.1 Equation 9 with :

SHe DSHh SHi

2340 psi 1868.0025 psi 9450.000 psi

g.2 Equation 10 with :

DSLh SHe SHi

1249.5 psi 2340 psi 9450.000 psi

g.3 Equation 11 with :

p

g.4 Effictive Stress, Seff Equation 12 with :

S1 S2 S3 S1 - S2 S2 - S3 S3 - S1

g.5 Check allowable effective Stress Equation 13 with :

F SMYS Seff

F x SMYS

300 psi

> OK

13658.003 4786.500 -300 8871.503 5086.500 -13958.003

psi psi psi psi psi psi

0.72 52000 psi 12235.233 psi Seff 

S1 = SHe + DSHh + Shi 13658.003 psi S2 = DSLh - Es x at (T2-T1) + vs (SHe + SHi) 4786.500 psi S3 =

-300 psi

Seff = 2 2 2 Sqrt [1/2{(S1-S2) + (S2-S3) + (S3-S1) }] 12235.233 psi

F x SMYS =

37440 psi

Step - h - Check Fatigue h.1 Girth welds Table 3 Equation 17 with :

F DSLh DSLh

<

0.72 1249.5 psi

for X52 steel SFG SFG x F

12000 psi 8640 psi

for X52 steel SFL SFL x F

21000 psi (ERW) 15120 psi

SFG x F

OK h.2 Longitudinal welds Table 3 Equation 17 with :

F DSHh DSHh

< OK

0.72 1868.0025 psi SFL x F