Evaluation of Underwater Pipeline Design Criteria Due to Safety

Requirement based Hydrodynamic and External Load

Widi Agoes Pratikto, Raditya Danu Riyanto, Silvianita, Rendatiyarso Laksono,

Muhammad Ilham Maulana, Wetta Inggrid Sari, Abiyani Choirul Huda and Liany Ayu Catherine

Department of Ocean Engineering, Faculty of Marine Technology, Institut Teknologi Sepuluh Nopember,

Surabaya, Indonesia

Keywords: Pipeline, Free Span, Rock Berm.

Abstract: Several problems can be solved by piping engineers to protect pipelines so it can be resistant to environmental

and man-made hazards. Factors that can damage the pipeline are usually shipwrecks, faults in dropping and

pulling anchors, dredging activities, fishing activities, and the exploration of undersea. Burial pipelines are

the solutions most often used by engineers for the protective pipeline. However, the burial of the pipeline

cannot always be applied due to unfavorable seabed issues or if there are other factors. This paper will explain

the results of research related to the pipeline by calculating the dimensions of rock berms to protect pipelines

from external loads and analysis of the free span pipeline to check the feasibility of being exposed to

environmental loads.

1 INTRODUCTION

The Oil and Gas Industry is an important sector in

national development both in terms of meeting the

needs of energy and industrial raw materials in the

country as well as producing foreign exchange so that

the management needs to be done as optimal as

possible. The underwater pipeline is one of the most

efficient long-distance transportation infrastructure for

oil and gas for the transfer of oil and gas production

both from exploration on land, near the coast and from

the deep sea with effective and efficient methods.

Failure in the pipeline system can be caused by various

problems, such as free span (due to environmental

loads), and anchor loads (external loads) from ships

that are leaning in the Madura Strait area. A free span

occurs due to vibration or commonly known as the

Vortex-Induced Vibration (VIV) phenomenon that

occurs in parts of the pipe that touches the seabed.

Stability analysis of the pipeline from the environ-

mental load (wave and current) is very important

because it can determine feasibility design of the

pipeline (length of the free span) that has been installed

so that in the future preventive steps can be planned for

the best. Pipeline protection from external loads is also

important because if the pipeline is hit by anchor load

it can cause damage such as buckling and pipe leakage

so that it disrupts the oil and gas distribution process

and causes environmental pollution.

2 RESEARCH DATA

In this study, the area to be analyzed is the Madura

Strait, and the pipeline that will be designed for rock

berm protection and free span analysis are the Block

BD pipeline. In the analysis of concrete armor design

(rock berm) design, an external load size calculation

will be performed. External loads have a big role in

damaging the pipeline system on the seabed, in this

case, the movement anchor from the seabed. In

determining the size of the anchor, an analysis of ship

mobility that often crosses the study area will be

carried out, namely the Madura Strait. The following

are the data used in this study:

Table 1: Ship Sailing Data in the Madura Strait.

(source: PT. Pelindo III)

Ship Type In 2012

Container Ship 2040

General Cargo Ship 2144

Bag Cargo Ship 558

Fuel Tank Ship 1264

Liq. Bulk Non Fuel Ship 447

Dry Bulk Ship 616

Barge 5908

Passenger Ship 1889

Pratikto, W., Riyanto, R., Silvianita, ., Laksono, R., Maulana, M., Sari, W., Huda, A. and Catherine, L.

Evaluation of Underwater Pipeline Design Criteria Due to Safety Requirement based Hydrodynamic and External Load.

DOI: 10.5220/0010047000300036

In Proceedings of the 7th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management (ISOCEEN 2019), pages 30-36

ISBN: 978-989-758-516-6

 2021 by SCITEPRESS – Science and Technology Publications, Lda. All r ights reserved

Table. 2: Ship Capacity Data in the Madura Strait.

(source: PT. Pelindo III)

Ship Type Max. Capacity

Passenger Ship 15.000 GT

Cargo Ship 5.000 DWT

Ferry Ship 10.000 DWT

Roro Ship 5.000 DWT

Tanker Ship 5.000 DWT

Figure 1: The waters map in the Madura Strait

(source : navionics.com and maps.google.com).

In this study for wind data, current velocity, and

wave data are at coordinates with longitude

113.066248 E and Latitude 7.567736 S over 5 years

namely 2014-2019 with ground data using granules

D50 = 0.03 m.

Table 3: Wind Data in the Madura Strait.

Date

Time

(GMT

+7)

Wind

Dir

(deg)

Wind

Speed

(knot)

High

Wave

Sign.

(m)

Curr.

Speed

(cm/s)

01-12-

2014

00.00 169.26 3.4 0.01 0.51

02-12-

2014

01.00 173.02 3.56 0.01 0.62

03-12-

2014

02.00 176.46 3.72 0.01 0.69

… … … …

13-07-

2019

17.00 144.27 2.08 0.01 4.28

14-07-

2019

18.00 139.43 1.99 0.01 4.45

15-07-

2019

19.00 134.2 1.93 0.01 4.61

Table 4: Pipeline Data.

Parameter Value Unit

Inner diameter of pipe 404.14 (16) mm (inch)

Wall thickness of pipe 13 (0.5) mm (inch)

Wall thickness of concrete 60 (2.4) mm (inch)

Nominal diameter 0.45 m

Allowable free span 23.8 (78) m (ft)

Length of pipe 53 km

Effective Mass 282.68 kg/m

Period 20 year

3 RESEARCH DATA

PROCESSING

3.1 Free Span Calculation

Free span calculation is used to determine the

maximum span length so that the stress that occurs in

the free span does not exceed the yield stress of the

pipe material. The flow of waves and currents that

arise around the pipe, arises a vortex that results in

pressure distribution. This vortex produces

oscillations/vibrations in the pipe. If the frequency of

this vortex approaches the natural frequency of the

pipe, resonance occurs, and this causes fatigue in the

pipe (Yong Bai, 1981).

3.2 Calculation of Critical Span Length

In Boyun Guo (2005), critical span length or pipe

length without support where oscillations occur due

to currents is a relationship between the natural

frequency of the pipe span and the reduced velocity.

The critical span length for cross-flow motion is

𝐿







𝐶



𝑈



𝐷

2𝜋



𝐸𝐼

𝑀



(1)

In Boyun Guo (2005), the natural frequency of a

pipe depends on the stiffness of the pipe, the

condition of the end of the pipe span, the span length,

and the effective mass of the pipe. The natural

fermentation equation of the pipe is as follows:

𝑓





𝐶



2𝜋



𝐸𝐼

𝑀



𝐿





(2)

Fn = frequency of pipe natural (Hz)

Evaluation of Underwater Pipeline Design Criteria Due to Safety Requirement based Hydrodynamic and External Load

Ls = longspan (m)

Me = massa of effectivity pipe (kg/m)

Ce = 9.87 pin-pin

E = 2.07 E+11 (N/m

)

I = 0.00018 (kg/m

)

The critical span lengths for in-flow motion are:

𝐿







𝐶



𝑓



2𝜋



𝐸𝐼

𝑀



(3)

Ls = Span long of critical (m)

Ce = Span end constants

Ur = Reduced Velocitty (m/s)

D = Diameter of outer pipe (m)

Me = Mass of effectivity pipe, (kg/m)

After the calculations we have:

Table 5: Critical length of span.

Parameter

Water Depth

42 m 43 m 44 m

54 m

cross flow

5 4.7 4.8

in flow

1.4 1.4 1.4

1.4

cross flow

(

)

34.57 33.52 33.87

34.57

0.48 0.51 0.5

0.48

in line (m)

16.49 17 16.83

16.49

For most projects, the allowable span length is the

critical span length calculated for in-line motion.

However, when economic factors are taken into

consideration, the length of the critical range

calculated for the cross-flow movement can be

chosen.

3.3 Free Span Due to Scouring

Spans in the pipeline can arise due to local scour of

sea-floor sediments or where the pipe routes through

the seabed are irregular. When the lower current

passes through the pipe, separately vortices are

formed from the top and bottom of the pipe. This

causes fluctuations in hydrodynamic forces which

can produce large oscillations or spans in the

direction of cross-flow when the frequency of vortex

shedding approaches the natural span of vibration.

Pipe failures which can be caused by vortex

movement can be prevented if the vortex shedding

frequency is far enough from the natural frequency of

the pipe stretch so that the dynamic oscillation of the

pipe can be minimized. The frequency of vortex

shedding can be written:

𝑓





𝑆𝑉



𝐷

(4)

fs = frekuensi vortex shedding

S = Strouhal Number

Ve = effective current speed (m/s)

D = Diameter of Pipe (m)

Strouhal number is a function of Reynolds'

number of current flow. The drag coefficient is also a

function of Reynolds' number.

The relationship between the drag coefficient with

the Strouhal number is:



For practical problems, usually, the Strouhal

number is taken at 0.2.

After calculating the results obtained as follows:

Table 6: Free Span.

Parameter

Water Depth

42 m 43 m 44 m 54 m

S 0.207 0.201 0.195 0.183

Free S

an 0.147 0.131 0.116 0.043

Mousselli (1981) states that the pipeline stretch

has begun to oscillate when the shedding frequency is

1/3 of the natural frequency of the vibration of the

pipe stretch. To design pipe vortex shedding

frequency comparison is smaller than 0.7 times the

natural frequency of the pipe stretch so that

oscillation does not occur. So it can be written that

oscillation does not appear if: fs ≤ 0.7 fn. Based on

calculations and limitations that fs ≤ 0.7 fn, the pipe

design in the BD block is feasible when viewed from

the scouring analysis of the free span, namely:

Table 7: Analysis of freespan.

Water

Depth

Parameter Check

fs fn 0.7 fn OK / NOT O

0.147 0.477 0.334 O

0.131 0.507 0.355 O

0.116 0.497 0.348 O

0.043 0.477 0.334 O

4 ANCHOR CALCULATION

4.1 Calculation of the Main Dimensions

of the Ship

Anchor calculations are performed to determine

dimensions, number of anchors needed, anchor

𝑆

0,21

𝐶



,

ISOCEEN 2019 - The 7th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management

weight, and chain dimensions. In this study, the

anchors of a 15000 GT Passenger Boat with 10000

DWT Ferry Ships will be compared with the

following data:

Table 8: Data of Ship Comparison for Passenger Ship

15000 GT.

(source: equasis.com)

Ship Name

)

DWT

(ton)

Lpp

(m)

(knot)

Nggapul

14739 3175 146.5 23.4 6

15.6

Sinabung

14716 3485 146.5 23.7 6

16.3

Bukit siguntang

14643 3686 146.5 26.5 5.7

15.5

Ciremai

14581 3480 144.8 26.8 5.5

Dobonsolo

14581 3500 146.5 23.7 6

15.7

Doro londa

14685 3175 146.5 23 5.9

15.1

Kambuna

14501 3434 144.8 23.7 5.9

17.4

Kelu

14665 3537 146.5 23.7 5.8

17.3

Lambel

14649 3685 136.03 23.7 5.5

15.9

Rinjani

14501 3434 144.8 23.7 5.7

17.1

Tida

14501 3200 144 23.7 6.1

15.4

Umsini

14501 3434 141 22 6

12.5

Table 9: Data of Ship Comparison for Ferry Ship 10000

DWT.

(source: equasis.com)

Ship Name

)

DWT

(ton)

Lpp

(m)

(knot)

Europalin

9653 46124 218.8 30.5 6.9

14.7

Finnlad

9653 45923 218.72 30.52 6.8

22.6

Finnmai

9653 45923 218.77 30.5 6.7

21.3

Finnsta

9653 45923 218.77 30.5 6.7

21.6

Finnswan

9653 45923 218.8 30.5 6.9

14.9

La superba

9750 49257 211.5 30.4 7.3

22.7

La suprema

9720 49257 211.5 30.4 7.2

22.8

Skane

8787 42705 200.2 29.6 5.9

11.2

Spirit of

ritain

9500 47592 212 31.4 6

16.7

Spirit of

france

9884 47592 212 31.4 6

14.8

Stena

adventure

9487 43532 211.56 29.88 5.5

sses

9665 50938 209.08 31.84 6.3

18.7

From comparison ship data tables 3.5 and 3.6 can

be made the relationship graph between GT and

DWT, GT with Lpp, GT with B, GT with T, and GT

with Vs for 15,000 GT Passenger Ship and also graph

the relationship between DWT and GT, DWT with

Lpp, DWT with B, DWT with T, and DWT with Vs

for 10,000 DWT Ferry Ships to determine the size of

the main dimensions of the ship to be measured

anchored using linear regression equations.

After obtaining a graph from the comparison,

from the linear regression above (each equation), the

values of the main dimensions of the 15,000 GT

Passenger Boat and the 10,000 DWT Ferry Ship are

as follows:

Table 10: The Main dimensions of Passenger Ships 15000

GT.

Parameter

Value

Units

15000

DWT

3429.5

ton

148.58

15.68

knot

Table 11: The Main Dimensions of Ferry Ships 10000

DWT.

Parameter

Value

Units

DWT

10000

ton

50156

221.5

30.3

6.5

19.2

knot

4.2 Determination of Ship Coefficient

Based on Froude numbers, CB can be calculated with

the formula Watson-Gilfilla, CM, and CWP can be

searched by equations in the book "Parametric Ship

Design" page 11. Furthermore, the length of LWL,

LCB, ∇, and Δ can be calculated, which are:

Froude Number (Fn):





 

= 0.412 (5)

CB : Block Coefficient:

−4.22 + 27.8 ∙ √(Fn ) – 39.1 ∙ Fn + 46.4 ∙ Fn (6)

CM: Midship Coefficient: 0.977 + 0.085 ∙ B − 0.6)

(7)

CWP: Waterplane Coefficient: 0.180 + 0.860 ∙ CP

(8)

LCB: Longitudinal Center of Buoyancy:

8.80 - 38.9 ꞏ Fn (9)

CP: Prismatic Coefficient: C_B/C_M (10)

∇: Volume Displacement: L ∙ B ∙ T ∙ CB (11)

Δ: Displacement: ∇ . ρ (12)

Where, ρ = 1.025 ton/m3

Based on the explanation and formula above the

results of the calculation of the coefficient of the ship

based on the dimensions of the ship obtained are as

follows:

Evaluation of Underwater Pipeline Design Criteria Due to Safety Requirement based Hydrodynamic and External Load

Table 12: The dimensions of the Passenger Ship 15000 GT

based on the coefficient of the ship.

Parameter Value Unit

Cb 0.75 -

Cm 0.99 -

0.76 -

0.84 -

Lcb 7.19

ehind of the midshi

Δ 805.69 m

∇

825.83 ton

Table 13: The Dimensions of the Ferry Ship 10000 GT

based on the coefficient of the ship.

Parameter Value Unit

Cb 0.76 -

Cm 0.99 -

Cp 0.77 -

0.84 -

Lcb 7.23

ehind of the midshi

Δ 1075.29 m

∇

1102.17 ton

4.3 Anchor Dimensions and Weight

Based on BKI Vol. II of 2001 section 18-2, the Z

number can be calculated using the following

formula:

Z = D2/3 + 2.h.B + A/10

(13)

Where,

D2/3: Represents the amount of water displaced

(displacement) when the waterline is in

summer in seawater which has ρ seawater

1.025 tons / m3

H: The effective height is measured from the line

of loading water in summer to the highest end

of the deck.

B: Ship Width

A: The area (m2) is the appearance of the hull

profile, superstructure and houses which have

a width greater than B / 4 which is above the

loading line in summer including length L and

above from height h.

LWL: LPP + (3% * LPP)

D2/3: (LWL x B x T x CB)2/3

In calculating h, it is assumed to be the upper

building and the deck is 2.4 m, so the upper building

and house building

h : Fb + ∑h

: (H-T) + (Number of Floors x Floor Height)

A: LWL x T

Calculate Equipment Number (Z) with the

following equation:

Z: D2/3 + (2 x h x B) + A/10 (14)

After calculating the results obtained are as follows:

Table 14: Calculation of Equipment Number (Z) of

Passenger Ship 15000 GT.

Parameter Value Unit

Lwl 153 m

D2/3 664.76 -

H 14.06 -

A 911.23 -

Z 1456.1 -

Table 15: Calculation of Equipment Number (Z) of Ferry

Ship 10000 DWT.

Parameter Value Unit

Lwl 228.14 m

D2/3 1048.2 -

H 15.43 -

A 1475.2 -

Z 2129.8 -

Based on the calculation, the Z value of the 15,000

GT Passenger Ship is 1456,104 while the Z value of

the 10,000 DWT Ferry Ship is 2129.88. From the

results of calculations prove that the 10,000 DWT

Ferry has a Z value greater than the Z value of the

15,000 GT Passenger ship. Because the greater the Z

value, the greater the anchor obtained from the BKI

table, so in this study we used the Z value of the

10,000 DWT Ferry with a Z value of 2129.88.

Based on the table BKI Volume II 2006

section 18, then with a value of Z = 2129.79 obtained

anchor data as follows.

• Number of anchor bower :2 anchr

• Anchor Bower Weight : 6450 kg

• Anchor Chain

Length : 605 m

Diameter D1 : 81 mm

D2 : 70 mm

D3 : 62 mm

• Mooring Rope

Amount : 5 pieces

Length : 200 m

Broken Load : 425 kN

• Pull Rope

Length : 240 m

Broken Load : 1260 kN

Anchor weight = 6450 kg, then from the

catalog obtained anchor dimensions that

will be used on this ship are:

A = 2920 mm

B = 2046 mm

C = 906 mm

D = 1885 mm

E = 1461 mm

ǾF = 110 mm

ISOCEEN 2019 - The 7th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management

4.4 Anchor Chain Determination

After getting the data from the anchor, the anchor

chain is selected from the catalog, namely by:

a. Total Length Selected: 605 m

b. Diameter of chain anchor selected: 81 mm

Komposisi dan kontruksi dari rantai jangka

meliputi:

1. Common link

1). 1,00 d = 81 mm

2). 6,00 d = 486 mm

3). 3,60 d = 291.6 mm

2. Enlarge Link

1) 1,1 d = 89.1 mm

2) 6,6 d = 534,6 mm

3) 4,0 d = 324 mm

3. End Link

1) 1,2 d = 97,2 mm

2) 6,75 d = 546,75 mm

3) 4,0 d = 324 mm

Based on the calculation of the dimensions that

have been obtained the following is an illustration of

the anchor size obtained from the calculation results

based on table Z BKI.

Figure 2: The dimension of anchor in the front look.

Figure 3: The dimension of anchor in the beside.

Figure 4: The dimension of pipe and layer in the concrete.

Figure 5: The comparison of Anchor and Pipe.

5 CALCULATION OF ROCK

BERM

The use of berm rock is a common practice to protect

pipes against collisions from fishing gear such as

trawlers and trawlers. Rock berms must be able to

withstand horizontal impact loads, which mainly

depend on the following:

• The shape and mass of a trawler

• Trawling speed

• Direction of attraction

• Seabed conditions

5.1 Dimensions of Rock Berm

The rule of thumb for the design of suitable protection

against anchor anchors has been derived from tests

carried out for 20 years and is mainly used in

connection with the following rock berm parameters:

• Protective stone size (D50)

• The thickness of the protective layer

• Filter layer thickness (if applicable)

• Minimum width of the rocky peak

• Minimum width of the berm rock base

Evaluation of Underwater Pipeline Design Criteria Due to Safety Requirement based Hydrodynamic and External Load

Below is a visualization of the structure of berm

rock based on the calculations:

Figure 6: Rock berm illustration.

Based on calculations, the dimensions of the stone

which can be sufficient against the drag anchor are as

follows:

Table 16: Rock Berm Dimension.

Rock berm

dimension

Value

50, armour

 4 * 81 mm = 0.32 m

min, armour

 1.46 m * sin(45) = 1.03 m

 3 * 0.32 m = 0.97 m

min, filter

 1.5 * 0.32 m = 0.49m

 0.3 m

min, top

 2 * 2.92m = 5.84m

min, bottom

 5.84 m + 2*2.5*(1.33+0.48

m) = 14.9 m

6 CONCLUSION AND

SUGGESTION

6.1 Conclusion

Based on the analysis, the free span parameters in the

pipeline show that they are still feasible and do not

require handling to overcome the free span. the

pipeline design to free span with a limit of fs ≤ 0.7 fn:

(Refer to Table 7).

Furthermore, from the analysis of the anchor

weight, the dimension of berm rock which is used as

protection for pipeline on the bottom of the sea from

anchor threats. Dimensions of rock berms are:

top

: 5.84 m

bottom

: 14.9 m

armour

: 1.03 m

(Refer to Table 16).

6.2 Suggestion

The suggestion of this research is:

When doing free span calculations it would be better

if done with 3D modeling, the author has not done 3D

modeling to provide a clearer visual appearance to the

reader.

REFERENCES

Arif, Umar., et. all. Analisa Freespan Akibat Scouring Pipa

Bawah Laut. Jurnal Teknik Kelautan ITS. Surabaya.

Bai, Yong, Bai, Qiang, 2010. Subsea Structural

Engineering Handbook. Gulf professional Publishing.

Great Britain

Bai, Yong, Bai, Qiang, 2005. Subsea Pipelines and Risers.

Elsevier. USA

Ciria, C683., 2007. The Rock Manual. London

DNV RP F105., 2002. Recommended Practices for

Freespanning Pipelines. Det Norske Veritas, Norway.

Guo, Buyon, et. all., 2005. Offshore Pipelines. Gulf

Professional Publishing. USA

Hertia, Arisanti, 2003. Studi Estimasi Scouring dan

Freespans Pada Pipa Bawah Laut PT. Exxonmobil di

Perairan Tuban, Jawa Timur. Surabaya

J.P., Kenny & Partner Ltd, 1993. Structural Analysis of

Pipeline Spans. HSE Books. USA

Naess, A., Almar, 1985. Fatigue Handbook Offshore Steel

Structure. Trondheim.

Nugraha, Muhammad Catur. et. All, 2012. Analisa

Pengaruh Scouring Pada Pipa Bawah Laut (Studi

Kasus Pipa Gas Transmisi SSWJ Jalur Pipa Gas

Labuhan Maringgai – Muara Bekasi). Jurnal Teknik

ITS. Surabaya

Putra, Sebrian Mirdeklis BP. et. all. Simulasi Numeris

Perubahan Morfologi Dasar Laut Pada Desain

Pelabuhan Di Kabupaten Gresik, Indonesia. Jurusan

Pengairan Fakultas Teknik Universitas Brawijaya.

Malang.

Putri, Rieska Mawarni. et. all. Desain Offshore Pipeline

Blok BD Selat Madura. Teknik Kelautan FTSL ITB.

Bandung

Soegiono, 2006. Pipa Laut, Airlangga University Press.

Surabaya.

Triatmodjo, B., 1999. Teknik Pantai. Beta Offset.

Yogyakarta

ISOCEEN 2019 - The 7th International Seminar on Ocean and Coastal Engineering, Environmental and Natural Disaster Management