i

MODULE: FUNDAMENTALS OF PIPELINE ENGINEERING

PPE 801.2: PIPELINE HYDRAULIC ANALYSIS & DEFECT ASSESSMENT ON PIPELINES

Course Lecturer: AKHIGBEMIDU Chris, Ph.D., R.Eng.(8057)

February 23-27, 2015

ii

TABLE OF CONTENTS

Page

NOTATIONS ii

TABLE OF CONTENTS iii

1 Introduction 1

2 Important Thermo-Fluid Concepts 3

3 Review of Thermodynamics Principles 3

3.1 The Laws of Thermodynamics 5

3.1.1 First Law of Thermodynamics 5

3.1.2 Second Law of Thermodynamics 6

3.1.3 Isoprocess 8

4 Pipeline Flow Calculations 9

4.1 Basic Principles of Fluid Flow in Pipes 9

4.1.1 Conservation of Mass Principle 9

4.1.2 Work-Energy principle 10

4.1.3 Principle of Impulse-Momentum 12

4.2 Reynolds Number 14

4.3 Darcy-Weisbach Pipe Friction Equation 15

4.4 Minor Energy Loses 18

4.5 Flow properties in pipelines 19

4.6 Basic Flow Calculations for Gases 20

4.7 Problems caused by changes in flow conditions 22

5 Definition and Types of Defects in Pipelines 23

5.1 Failure Statistics and Relative Causes of Pipeline Failures 24

6 Failure Modes and Description of how Pipelines Fail 26

6.1 Effect of Manufacturing and Installation Defects 27

6.2 Effect of Corrosion 29

6.3 Effect of Operational Pressure Surges 29

iii

6.4 Influence of Ground Movement on Pipelines 30

6.5 Effect of Environmental Activities and Pipeline Intrusion 30

7 Defect Assessment 32

7.1 Design Code and Standard Requirements 33

7.1.2 Pipeline Defect Assessment Manual (PDAM) 33

7.1.2 The API 579-1/ASME FFS-1 Standard 36

7.1.3 RSTRENG and the Modified B31G criteria 39

8. Introduction to Pipeline Engineering Critical Assessment (ECA) 46

REFERENCES 48

APPENDIX I: GLOSSARY OF TERMS AND DEFINITIONS 50

1

1 Introduction

In Course PPE 801.1, we defined a pipeline as an assembly of linepipes

continuously strung together by welding (or other such means of joining)

and devices such as pumps, compressors, valves, swivels, metering

stations, regulator stations, manifolds, risers, pig launchers/receivers and

other accessories for conveying a fluid from one point to another. We

stated that the driving force in a pipeline is by virtue of the pressure

differential that is generated by pumps and compressors between the inlet

and outlet.

We surmised that not every hollow piping system used in fluid

transportation could be classified as a pipeline in the strict sense of ASME

B31 code which is the basis of pipeline design, operation and maintenance,

amongst other similar codes.

Factors affecting design of a pipeline were outlined. We emphasized that

maintaining the structural integrity of a pipeline throughout its design life

is crucial in its design, installation and operation.

We equally identified flow computations/simulations and determination of

power requirements as part of the critical design tasks in a typical pipeline

project, hence the need for hydraulic analysis.

We concluded that pipelines are usually classed as part of a nations

critical infrastructure and that an extensive pipeline network goes hand-in-

hand with a high standard of living and technological progress of a nation.

2

We observed that Nigeria has not had a good history of safety in the

management of its pipeline infrastructure and that cases of incessant

failures of pipeline assets have been dominant in the last decade, traced

partly to ageing assets, corrosion flaws, poor operation and maintenance

practices, and partly to illegal activities of vandals resulting in

environmental pollution, monumental waste of human and material

resources.

Hydraulic analysis and assessment of defects in pipeline systems in order

to understand how flows are analyzed, defects assessed and failures

prevented are at the core of this module.

3

2 Important Thermo-Fluid Concepts

A system is an arbitrary collection of matter of fixed identity.

The surroundings of a system implies everything external to the system.

The boundary of a system implies an imaginary surface which separates

the system from its surroundings.

The system and the surroundings together are called the Universe.

An open system is that which exchanges both matter and energy with its

surroundings.

A closed system is that which exchanges energy, but not matter, with its

surroundings.

An isolated system is that which does not exchange matter or energy

with its surroundings.

Control volume is an arbitrary volume fixed in space, through which

fluid flows. As fluid moves through the control volume, the mass

entering the control volume is equal to the mass leaving the control

volume.

Control Surface bounds the control volume and is always a closed

surface which may be finite or infinite.

The state of a system is its condition or configuration, described in

sufficient details so that one state may be distinguished from all other

states.

A property of a system is any observable characteristic of that system

such as location, speed, direction, pressure, density, temperature etc. A

listing of a sufficient number of independent properties that constitute a

complete definition of the state of a system.

4

Process is a change of state, described in part by the series of states

passed through by the system and often, some by same sort of

interaction between the system and its surroundings.

A cycle is a process wherein the initial and final states of the system are

identical. For this to be true, therefore, the initial and final properties of

the system must be have identical values.

A fluid as a substance which deforms continuously under the action of

external shearing forces (Rajput, 2008). Fluids have no definite shape

and they thus conform to the shape of the containing vessel. A small

amount of shear force exerted on a fluid causes it to undergo continuous

deformation as long as the force continue to be applied.

An ideal fluid is one that has no viscosity and surface tension and is

incompressible.

5

3 Review of Thermodynamics Principles

Thermodynamics is the study of energy which treats the relations among heat,

work and the properties of the systems in equilibrium.

According to Braestrup et al. (2005), thermodynamic simulations have to be

performed in each segment of a pipeline in order to evaluate the conditions

of the flowing medium (i.e. oil, gas etc.). For instance, in a gas pipeline,

such analysis could predict liquid dropouts and hydrate formation

phenomena which if not contained can lead to serious operational problems.

While for a liquid pipeline, dissolved gases in oil could lead to capacity

reduction, air pockets, cavitations problems etc. Wax formation, ice

formation, hydrate formation and associated problems due to sudden

changes in apertures, valve throttling etc. can also be resolved through

thermodynamic analysis. Typically, thermodynamic systems are grouped

into open, closed or isolated systems.

3.1 The Laws of Thermodynamics

The laws of thermodynamics deals with systems and their surroundings as

they respectively pass through equilibrium states. These interactions may be

divided into:

Work Interaction and

Heat Interaction

3.1.1 First Law of Thermodynamics

The First Law of Thermodynamics states that energy can be changed from

one form to another, but it cannot be created or destroyed. The total amount

of energy and matter in the universe remains constant, merely changing

from one form to another. Therefore, energy is always conserved, it cannot

6

be created or destroyed, it is only converted from one form into another.

Consequently, the amount of work done by any system in going from one

state to another does not depend on the course of states passed through by

the system nor on the manner of work interaction, so long as the system and

surroundings are equal in temperature at each step of the process.

Corollary: The amount of work done during an equal temperature process

depends only on the end-states and not on the intermediate series of states.

WE (3.1)

Where

E internal energy required to do work = Initial (E1) - Final (E2).

The actual work done is

WEQ (3.2)

In differential form

WdEQ (3.3)

From (3) we obtain the first law for a cycle thus

WQ (3.4)

Where

dE an increment of a property of the system (i.e. internal energy).

WE & small amounts of quantities which are not properties of the

system.

Eq.( 3.4) implies that the algebraic net heat received by system during a

cycle is equal to the algebraic net done by the system during the cycle.

3.1.2 Second Law of Thermodynamics

The Second Law of Thermodynamics states that in all energy exchanges, if

no energy enters or leaves the system, the potential energy of the state will

always be less than that of the initial state. This is also commonly referred

to as entropy.

Entropy is the subject of the second law, while energy is the subject of the

first law.

7

Entropy is a property of thermodynamical systems. In a thermodynamic

system, pressure differences, density differences, and temperature

differences all tend to equalize over time. The dispersal of energy from

warmer to cooler regions always results in a net increase in entropy. Thus,

when the system of the room and ice water system has reached temperature

equilibrium, the entropy change from the initial state is at its maximum. The

entropy of the thermodynamic system is a measure of how far the

equalization has progressed. Entropy represents the unavailability of a

system's thermal energy for conversion into mechanical work, often

interpreted as the degree of disorder or randomness in the system.

In a reversible process thermodynamic cycle

0

revT

Q (3.5)

Eq. (3.5) implies that going from a given state (1) to (2) by two processes

(both of which are reversible) the integral of T

Q will be the same for both

processes and we say the TQ

depends on the end states and not on the

intermediate series of steps.

Thus, the quantity T

Q for a reverisble infinitesimal process is therefore an

exact differential of a thermodynamic property called the entropy defined

by

revrev T

Q

T

Qds

(3.6)

8

TdsQrev (3.7)

Now, for internal energy and entropy, which are both properties of a fluid in

a given system, Rajput (2008) holds that it is more convenient and useful to

express the properties in specific values (i.e. the values per unit mass) thus

m

Ee (3.7)

and

m

Ss (3.7)

Where

E = internal energy for the entire system

S = entropy for the entire system

e = specific internal energy or internal energy per unit mass

s = specific entropy or entropy energy per unit mass

3.1.3 Isoprocess

An ISOPROCESS is one in which one of the thermodynamic variable

(state) is kept constant. The can be pressure, temperature or volume,

respectively known as

(i) Isobaric process

(ii) Isothermal process

(iii) Isochoric process

9

4 Pipeline Flow Calculations

Essentially a pipe is a closed conduit of circular section through which the

fluid flows filling the complete cross-section. Such a flow is termed a pipe

flow only when the fluid completely fills the cross section and there is no

free space in the pipe. Thus, a partially filled pipe is not regarded as a

pipeline and may only be treated as an open channel or closed drain.

4.1 Basic Principles of Fluid Flow in Pipes

In the hydraulics of pipe flows, there are three fundamental principles of viz:

The principle of conservation of mass (generally referred to as the

continuity equation in the case of steady incompressible flow).

The work-energy principle (modified classical Bernoulli equation).

The principle of Impulse-Momentum.

4.1.1 Conservation of Mass Principle

The continuity equation is based on the principle of conservation of mass. It

states that if no fluid is added or removed from the pipe in any length (such as

illustrated in Figure 1), then the mass passing across different sections remains

unchanged i.e.

Mass of fluid entering the CV per unit time = Mass of fluid leaving the CV per unit time .

Fig. 1: Idealization of fluid flow in Pipe

Control Volume

2

1

A1

V1

1

A2

V2

2

Datum

z2

z1

10

Thus from Figure 1,

222111 VAVA (4.1)

Where

1, 2 = density of fluid entering and exiting the CV respectively.

A1, A2 = cross-sectional area of entry and exit respectively

V1, V2 = entry and exit velocity of fluid into the CV respectively

Equation (4.1) is applicable for both compressible and incompressible flows.

For the case of an incompressible flow, the density of the fluid is constant and

thus eq. (4.1) reduces to,

2211 VAVA (4.2)

Now the discharge, Q is defined as AVQ and thus

21 QQ (4.3)

Note: the continuity equation can be similarly derived for two-dimensional and

three-dimensional flows and could be expressed in Cartesian and polar

coordinates, depending on the type of flow being analyzed.

4.1.2 Work-Energy principle

Recall that in the previous Course we stated that the driving force in a pipeline

is by virtue of the pressure differential that is created between the outlet and

inlet (Breastrup et al., 2005). The latent energies in the fluid creates the

pressure differential which in turn results in the flow of the fluid from one

point to another. These energies (or heads) at play in the flowing can be

classified into the following:

(i) Potential Head/Energy

(ii) Velocity Head or Kinetic Energy

11

(iii) Pressure Head or Energy

(iv) Accumulated (sum) head loss per unit weight between inlet and

outlet of the pipe or energy gain due to mechanical energy per unit

weight added to the flow by say an export pump (+ve if energy is

added to system and negative if energy is extracted from the system)

Now, for an ideal incompressible one-dimensional flow, the classical

Bernoulli's equation states that the total energy (head) of the fluid is constant

along a flow stream i.e.

w

P

g

Vz

2

2

constant (4.4)

However, because all fluids are real (and not ideal), hence losses are created

due to friction, viscosity, and thus eq. (4.4) is

Lhw

P

g

Vz

w

P

g

Vz 2

2

22

1

2

11

22 (4.5)

Where the terms

z = potential energy or elevation head.

g

V

2

2

= the velocity head or kinetic energy.

w

P = the pressure head.

hL = accumulated energy (loss and gain) due to friction effects and

energy added due to hydraulic power machinery.

12

4.1.3 Principle of Impulse-Momentum

The momentum equation relates the sum of the forces acting on a fluid element

to its acceleration or rate of change momentum in the direction of the resultant

force. The equation is one of the basic tools (the other being continuity and

work-energy equations) for the solution of flow problems.

This principle derives from Newton's second law of motion. Recall, in

mechanics, the force acting on a particle or an object is defined as the product

of its mass and its acceleration

F = ma (4.6)

Where

m = mass of the particle

a = acceleration of the particle in the direction of F.

But dt

dVa . Substituting a into eq. (4.6),

dt

mVd

dt

dVmF (4.7)

mVddtF . (4.8)

Equation (4.7) is the momentum principle, while eq. (4.8) is the impulse

momentum equation in which dV is the change of momentum in the direction

of F.

In a flowing fluid the momentum equation implies that net force acting on a

mass of fluid is equal to change in momentum of flow per unit time in that

direction. For steady, incompressible, one-dimensional flow through a pipe,

the component momentum equation along the direction of flow in the control

13

volume in Figure 1, the rate at which momentum exits the CV across 2 may be

defined as 222 VA and 111 VA at flow entry. Therefore, the rate of change of

momentum across the control volume is

)(.. 1211112222 VVmVVAVVA (4.9)

Where

AVm = the fluid mass flow, kgs-1

The increase of momentum per unit time will be caused by a force, F acting on

the fluid element in the CV in the direction of motion thus

12 VVmF (4.10)

Equation (4.8) is for one-dimensional flow, the 2D and 3D flows can be

similarly developed.

Note: Flow is described as one-dimensional flow if the factors or parameters,

such as velocity, pressure and elevation, describing the flow at any given

instant vary along the direction of flow and not across the cross-section at any

point. Typically in 1-D flows, the flow parameters are functions of time and

one-space co-ordinate only. An example of such flow is that in a pipeline.

The total quantity of fluid flowing per unit time past any cross section of the

stream is called the discharge or flow at that section. It may be measured in

terms of mass in which case it is referred to as the mass flow rate (kg/s) or in

terms of volume, known as volume rate of flow Q(m3/s).

VAQ (4.11)

Where

V = mean velocity.

14

Loses of energy in a pipe are due to frictional resistance to flow and shock

from the disturbance of the normal flow due to bends or sudden changes of

section etc.

4.2 Reynolds Number

Broadly, fluid flows can be divide into Turbulent (disorderly) flow and

Laminar (streamline or orderly) flow. Turbulent flow in pipes is characterized

by randomized, irregular and haphazard movement of fluid particles. The

nature of flow in a pipeline is determined by velocity of flow, density,

viscosity, size of pipe etc. The Reynolds number relates these fluid-pipeline

interface properties empirically thus

VDVDRe (4.12)

Where

Re = Reynolds number

= density,

V = velocity,

D = pipe diameter,

= viscosity,

= kinematic viscosity =

Reynolds number is essentially a ratio of the inertia force to the viscous force.

In equation (1) if:

Re < 2100 => flow is classified as viscous (laminar);

2100 Re 4000 => flow is classified as unpredictable;

Re > 4000 => flow is turbulent.

15

p

1 p

2 D

4.3 Darcy-Weisbach Pipe Friction Equation

Viscosity is a property of a fluid which determines its resistance to shearing

stresses. A fluid at rest has no shear forces acting, while a fluid in motion has

shear forces set up due to viscosity and turbulence which oppose motion, thus

producing frictional effect.

When a fluid flows in a pipeline, it experiences some resistance to its motion

due to which its velocity and ultimately the head (energy) available to transmit

its contents is reduced. These loss of head may be classified into:

Major energy losses due to friction.

Minor energy losses due to sudden changes in size of pipe (enlargement

or contraction), bends, internal obstructions, pipe fittings etc.

In a typical pipeline design, it is important to calculate these losses in order to

determine the proper size of pipes, bends, branches, capacity of the

pumps/compressors and other appurtenances required.

The loss of head due to friction could be calculated using the Darcy-Weisbach

equation as now discussed.

Fig. 2: Idealization of Friction in a Pipeline

Control length, L

1 2

16

Considering the control volume enclosed between sections 1 and 2 in Figure 2,

the driving force between the two points is

F = (p1-p

2) x A (4.13)

Let f ' be a non-dimensional factor whose value depends on the material and

nature of the pipe, the frictional resistance force

R= f 'LV

2 (4.14)

Therefore, under equilibrium and steady flow conditions

(p1-p

2) x A = f

'PLV

2 (4.15)

Dividing eq. (3) by weight density, w yields

2'

21 LVA

P

w

f

w

pp

(4.16)

Multiplying eq. (4) x g

g

2

2yields the loss of head (energy lost per unit volume)

due to friction as

g

VL

A

Pf

w

gh f

2

2 2'

(4.17)

Let mP

A => hydraulic mean depth (hydraulic radius) and '

2f

w

g = constant =

f; then,

g

V

m

Lf

g

VL

mfh f

22

1 22

(4.18)

Now for a pipeline, the hydraulic depth, m = 4

42

D

D

D

P

A

and thus

substituting m into eq. (6) yields

17

g

V

D

fL

g

V

D

Lfh f

2.

4

2.

4

2

2

(4.19)

Where

p1, p

2 = inlet and outlet pressure

A = cross-sectional area of pipe

P = perimeter cross-section, wetted perimeter.

V = mean velocity of flow

w = g = weight density (or specific weight)=weight per unit volume.

g = gravitational acceleration.

f = Darcy-Weisbach coefficient of friction which is a general

function the Reynolds Number and the relative roughness of

the pipe thus:

41

0791.0

eR

for Re varying between 4000 to 106

eR

16 for Re < 2000.

Eq. (7) is the Darcy-Weisbach equation and holds good for all types of flows

provided a proper value of f is known.

f is usually estimated from a standard Moody chart (refer to standard text

books) which relates a logarithmic plot of f vs Re for a range of k/D values

(relative roughness ratio) for a fully developed flow. k being the size of the

wall roughness (also called grain roughness) as typified in Table 1.

18

Table 1: Wall Roughness Factor of Common Pipeline Materials

Material K(mm)

PVC pipes 0.0015

Commercial Welded Steel 0.045

Cast Iron 0.26

Galvanized Iron 0.15

By suitable parameter manipulation, equation (4.19) can be recast and in terms

of flow rate thus

5

2

3D

fLQh f

(4.20)

Where

Q = discharge, m3/s

4.4 Minor Energy Loses

Minor losses arising from pipeline expansion/contraction, flow obstructions,

bends, valves etc. can be computed as follows (Douglas et al., 2005 and

Rajput, 2008):

i). The head loss due to sudden enlargement is

g

VVhe

2

2

2

2

1

(4.21)

ii). The head loss due to sudden contraction is

g

VV

w

pphc

2*

2

2

2

1

2

2

2

1

(4.22)

iii). Head loss due to obstruction is

22

02

1)( g

V

aAc

Ah

c

(4.23)

iv). Head loss at the entrance of a pipe

2

25.0

g

Vhn

(4.24)

19

v). Head loss at the exit of a pipe

2

2g

Vhx

(4.25)

vi). Head loss due to pipe bend

2

2g

Vkh bb

(4.26)

vii). Head loss due to various pipe fittings - tees, O' lets etc.

2

2g

Vkh ff

(4.27)

Where

V1 = mean velocity before enlargement

V2 = mean velocity after enlargement

p1 = inlet pressure prior to contraction

p2 = outlet pressure after contraction

A = cross-sectional area of pipe

a = maximum area of obstruction

cc = coefficient of contraction

kb = coefficient of bend

kf = coefficient depending on the type of fitting.

4.5 Flow Properties in flow in pipelines

In the analysis of compressible fluids, the relevant properties are:

density,

pressure,

shear stress,

velocity,

coefficient of viscosity,

temperature

internal energy (enthalpy),

entropy,

coefficient of thermal conductivity

20

4.6 Basic Flow Calculations for Gases

All fluids are compressible to varying degrees, but gases are more

compressible than liquids.

The analyses of compressible fluids must necessarily begin (either directly or

indirectly) with statements of the four basic physical laws governing such

motions:

Law of conservation of mass

Newton's law of motion

The first law of Thermodynamics

The second law of Thermodynamics

In addition to these fundamental principles, depending on the nature of the

particular fluid, it is usually necessary to bring into an analysis certain

subsidiary laws relating to the particular fluid e.g. the equation of state of a

perfect gas, the proportionality law between shear stress and rate of

deformation in a Newtonian fluid etc.

For instance, in order to predict the pressure drop, the properties of the gas

must be calculated along the pipeline length to reflect the changes with

pressure and temperature (Mohitpour, 2000).

The input parameters used for gas flow include operating pressure, temperature

and internal roughness. The steady-state hydraulic analysis involves reviewing

flows and pressure drops, determining capacity, pipeline diameters, pipeline

loop lengths and overall compressor station power requirements in the design

process. It begins with creation of a demand and forecast by examining all

21

existing and potential customers and creating a projection of their demand

requirements over a predetermined period.

As an example, consider a gas pipeline segment which transports gas at steady

gas flow from point (1) to (2) as illustrated in Figure 3

Fig. 3: Gas flow through a pipe Segment

Under steady flow state

0dt

dm

=> rate of change of mass is constant.

From eq.(4.9) the mass flow rates of gas at point (1) and point (2) are

respectively

1111 VAm (4.28a)

2222 VAm (4.28b)

Where

= gas density

p= gas pressure

A = cross sectional area of pipeline

V = gas velocity

m = mass of gas flowing in the system

t = time

______ . __________ . ________

1 2

A2 p2

2

m2

A1 p1

1

m1

22

Since dm/dt is constant

222111 VAVA (4.29)

Assuming the diameter of the pipe is constant, then

2211 VV

AVm (4.30)

Now by definition from thermodynamics, v

1

Where v = the gas specific volume

Now let CV = a constant

v

VC (4.31)

Hence eq. (4.30) becomes

v

VAm (4.32)

The impulse-momentum principle can then be used to formulate the acting

force on the gas.

4.7 Problems caused by changes in flow conditions

Inlet or supply pressures and outlet (demand) flows may vary with time,

leading to several problems. For instance, in gas pipelines, liquid dropouts and

hydrate formation which if not contained can lead to serious operational

problems. For a liquid pipeline, pumping excessive gas dissolved in oil could

lead to air pockets, capacity reductions, cavitations problems etc. Wax

formation, ice formation, hydrate formation and associated problems due to

sudden changes in apertures, valve throttling etc can resolved through thermo-

fluid analysis.

Exercise: Identify and explain the effect of fluid and flow conditions on

(a) Crude Oil Pipelines

(b) Gas pipelines

23

5 Definition and Types of Defects in Pipelines

ASME B31.8 (2012) defines a defect as a physically examined anomaly with

dimensions or characteristics that exceed acceptable limits, while API 5L

(2004) defines a defect as imperfection of sufficient magnitude to warrant

rejection of the product based on the stipulations of the applicable

specification. Therefore, defect is relative to the code or specification under

which an item is being studied. An item regarded as defective in one

circumstance may not necessarily be classified as defective in another.

Generally, a defect may, therefore, be viewed as an anomaly/irregularity

which may have a deleterious effect on the structural integrity of the pipeline

and consequently its ability to contain or transmit internal pressure and hence

failure.

O Connor (1992) has broadly defined failure as the termination of the ability

of an item to perform a required function. Matthew (2001) posits that

although failure in the strict sense of mechanical engineering means a

condition in which a component exhibits irreversible plastic deformation;

failure would also include such events as damage in which some deformation

has occurred relative to the as new condition of the component, which

renders the component unable to perform the service for which it was

designed. In pipelines, failure can be said to have occurred when there is an

unintentional release of process fluids from a pipeline transmission system into

the surrounding environment. Unintentional meaning the operator/owner did

not carryout actions that should activate a release.

24

McAllister (2002) has broadly classified defects causing failures in pipelines

into:

Manufacturing defects

Environmentally caused defects

Construction defects and defects caused by outside forces.

Thus, defects in pipelines could be due to latent imperfections in the parent

material (i.e. defects in the linepipe itself incurred during manufacturing), the

filler metal, welding procedures or wrong practices used during

transportation, installation and operation, as well as external damage (third

party activities) and deterioration(wear, erosion, corrosion etc.) of the

pipeline over time.

5.1 Failure Statistics and Relative Causes of Pipeline Failures

According to Yo-Essien (2008), compared to other parts of the world,

pipeline sabotage is currently the major cause of oil spills and pipeline fire

outbreaks in Nigeria. The crude oil and product pipelines have been the

major target of intrusion-induced failures. Between 2005 and 2008, there

were 11,503 reported cases of failure in Nigerian National Petroleum

Corporation (NNPC) pipeline network as detailed in Table 2, out of which

11,350 cases were attributed to intrusive vandalism. The trend is still

continuing with 3,570 line breaks reported in 2013 in NNPCs pipeline

network, out of which 3,305 were allegedly due to illegal intrusions and 34

cases of pipeline fires reported (NNPC Annual Statistical Bulletin, 2013).

25

Table 2: NNPC Product Pipeline Failure Data

Year Total No. Line

Breaks Recorded

Causes No. of Fire

Outbreaks No. Attributed

to vandalism

No. Attributed to

Rupture/Others

2005 2,258 2,216 21 117

2006 3,683 3,625 18 39

2007 3,244 3,224 20 18

2008 2,318 2,285 33 25

Total 11,503 11,350 92 199

(Source: Compiled from NNPC Annual Statistical Bulletin, 2005-2008)

Table 3 is a ten-year failure/spill history for Shell Petroleum Development

Company of Nigeria (SPDC). 70% of the spills were allegedly due to illegal

intrusions, while the balance was attributed to equipment failure, corrosion,

obsolescence, wear and tear, human factors etc.

Industry wide, pipeline intrusions is on the increase and seems to be

continuing unabated. Ogbeifun (2007) estimates that there were 46 fire

incidents in 2000 and 117 in 2005. Shell is only one of the five major oil

and gas producing companies, pipelines of other companies are not spared.

Table 3: Shell (Nigeria) Oil Spill Data

Year No of Spills Volume in

Barrels (bbl)

Equivalent Volume

(m3)

1995 235 31,000 4,928.61

1996 326 39,000 6,200.50

1997 240 80,000 12,718.98

1998 248 50,000 7,949.37

1999 320 20,000 3,179.75

2000 330 30,100 4,785.52

2001 302 76,960 12,235.66

2002 262 19,980 3,176.57

2003 221 9,916 1,576.52

2004 236 8,317 1,322.30

2005 224 11,921 1,895.29

Total 2,944 377,194 59,969.06

1barrel = 42 US gallon = 158.9873 litres =0.158983 m3

(Source: Shell Annual Report Adapted from Ogbeifun, 2007)

Foregoing statistics shows that pipeline failure is a contemporary problem

besetting the pipeline industry in Nigeria, with vandalism as the major

cause.

26

6 Failure Modes and Description of how Pipelines Fail

Though pipelines are meticulously designed to provide the safest means

of hydrocarbons transportation, there have been recurrence of serious

pipeline failure incidents in Nigeria resulting in spillages, loss of lives

and properties, and destruction of vast acreages of the environment, most

times irreversibly.

Chuan and Loong (2009) has identified some common modes of piping

failure as static stress rupture, fatigue failure, creep rupture, stability

failure, as well as some variants of these modes of failure.

Two possible failure modes, brittle and plastic collapse are often

considered for girth welds containing welding defects. However, in

modern pipelines the possibility of brittle fracture is often less likely

because modern linepipes have proven high material toughness

properties. Mohitpour et al (2000) have outlined where an otherwise

ductile material becomes brittle and thereby leading to failure. Thus, even

when a ductile linepipe becomes brittle, it is usually by ductile fracture

whereby the fracture initiates and propagates in the pipeline material with

significant plastic deformation at the fracture surface.

There are several reasons why pipeline structures fail. However, these

could be loosely grouped depending on the initiating

mechanism/phenomenon causing the failure as now discussed.

27

6. 1 Effect of Manufacturing and Installation Defects

API classifies and defines various types of defects which lead to pipeline

failures as abridged in Table 4.

In Nigeria, seamed pipelines are gradually being phased out with

seamless linepipes. There are still a number of operators using seamed

piping in their in-plot piping facilities, especially those installed prior to

1975.

Table 4: API Classification of Defects in Line pipes

Class of Defect Type Defect Description

A. General Defects

General

O.D. defect

A defect emanating at and extending radially inward from

the outside surface but not entirely through the wall of the

pipe.

I.D. defect

A defect emanating at and extending radially outward

from the inside surface but not entirely through the wall of

the pipe.

Interior

defect

A defect emanating in the interior of the pipe wall but not

of sufficient radial extent to be connected with either the

inside or the outside surface.

Leaking

O.D. defect

A defect which was initially an O.D. defect, but which has

grown through the wall to become a leak.

Superficial

defect

A lap, crevice, pit, group of pits, metallurgical anomaly, or

plain dent (i.e. without scratches, gouges, or cracks) which

is of insufficient extent to reduce the effective strength

level of the pipe below 100 percent of SMYS.

B. Defects originating from pipe manufacture

1. Defects not

necessarily in

the seam weld

(primarily in the

body of the

body of the pipe

Lap

Fold of metal which has been rolled or otherwise worked

against the surface of rolled metal, but has not fused into

sound metal.

Pit A depression resulting from the removal of foreign

material rolled into the surface during manufacture.

Rolled-in

slugs

A foreign metallic body rolled into the metal surface,

usually not fused.

Seam

Crevice in rolled metal which has been more or less

closed by rolling or other work but has not been fused into

sound metal.

Hard spot

An area in the pipe with a hardness level considerably

higher than that of surrounding metal: usually caused by

localized quenching.

Crack

A stress-induced separation of the metal which, without

any other influence, is insufficient in extent to cause

complete rupture of the material.

2. Defect which

occur in the

Incomplete

fusion

Lack of complete coalescence of some portion of the

metal in a weld joint.

28

seam weld

Incomplete

penetration

A condition where weld metal does not continue through

the full thickness of the joint.

Under-cut

Under-cutting on submerged-arc-welded pipe is the

reduction in thickness of the pipe wall adjacent to the

weld where it is fused to the surface of the pipe

Weld area

crack

A crack that occurs in the weld deposit, the fusion line, or

the heat-affected-zone. (Crack is a stress-induced

separation of the metal which, without any other

influence, is sufficient in extent to cause complete rupture

of the material.)

Upturned

fiber

imperfection

Metal separation, resulting from imperfections at the edge

of the plate, parallel to the surface, which turns toward the

I.D. or O.D. pipe surface when the edges are upset during

welding.

Penetrator A localized spot of incomplete fusion.

Cold weld

A metallurgical term generally indicating a lack of

adequate weld bonding strength of the abutting edges, due

to insufficient heat and/or pressure. A cold weld may or

may not have separation in the weld line.

(Source: Abridged from McAllister, 2000; BS 499 Part I, 1991)

At the installation phase, the most common method of field joining

remains the shielded metal arc welding (SMAW) process. Although the

process has undergone several improvements over the years, lots of

manufacturing imperfections are still found in such welded joints, which

eventually lead to field failures. Construction defects including a girth

weld anomalies, arc strikes, grindings, partial buckling, ovalizations,

dents, gouges etc. are some of the defects incurred during installation.

Also, during construction, pipelines are usually made to fit-the-ditch

and more often this practice is a source of several problems ranging from

residual stress failures to stress-induced corrosion, amongst others.

BS 499 Part I (1991): Welding Terms and Symbols (Glossary for

welding, brazing and thermal cutting) provides a comprehensive list and

description of defects in welded structures (including pipelines).

29

6.2 Effect of Corrosion

The combination of corrosion and stress acting together leads to stress-

corrosion cracks. Hydrogen stress cracking appears in hard spots attacked

by hydrogen emitted from sulfate reducing bacteria (SRB) acting

externally on the walls of the pipe. The attack commences chemically

when the iron ferrous ions liberate small quantities of hydrogen, while the

bacteria live by catalyzing the reaction, thereby removing the hydrogen.

This permits dissolution of the iron, whilst the liberated sulfide ions react

with the pipe to form ferrous sulfide, thus transforming the entire pipe

wall thickness to weak and porous ferrous sulfide, and as such, cracking

and eventual rupture of the line occurs.

6.3 Effect of Operational Pressure Surges

Fluid flowing in a pipeline undergoes a number of transient, or unsteady

flow-state conditions caused by such events as prime movers starting and

stopping, valves opening and closing and flows either in or out of the

pipeline resulting in pressure surges (SIPM, 1991). Acting together with a

corrosion defect, operational surges can lead to very serious problems.

Manifold valves, export pumps, compressors etc. due to frequent

community unrests and other factors are indiscriminately opened and

closed, often times against high pressure, which adversely reduces the

pipelines ability to contain internal pressure, especially at

corroded/eroded points.

30

6.4 Influence of Ground Movement on Pipelines

Pipelines can be affected by a number of ground movement events

leading to a wide range of ground loading conditions which may

sometimes result to catastrophic failures. According to Leach and Young

(1999), the nature and form of ground disturbance, properties of the soil

surrounding the pipeline, depth of cover, as well as the restraints imposed

longitudinally and laterally have strong influence on failure during

ground movements.

There are several types of ground movements that can lead to pipeline

failures in Nigeria e.g. erosion (mostly in the hilly eastern and middle

belts), floods, the uncontrolled use of mining explosives near pipeline

Right of Way (ROW) due to illegal mining activities, river shoring etc. A

landslide was very recently reported in Benue state (The Guardian,

Thursday, November 11, 2010). This shows that Nigeria is not immune to

natural or manmade earth faults as has been erroneously assumed over

the years.

6.5 Effect of Environmental Activities and Pipeline Intrusion

Dents and gouges and a combination of gouge-in-dent resulting from

human activities and external encroachment by mechanical excavating

equipment and other kinds of earth working equipment around the

pipeline Right of Way (ROW), have often been reported as reasons for

pipeline failures. For sea lines, the major hazards are ships anchors and

trawling.

31

Closely associated with accidental damage is the phenomenon of

deliberate and malicious intrusion into pipelines through such illegal

activities as pipeline harvesting, flowlines and outright

sabotage/vandalism for socio-political and economic reasons. The result

has been devastating and vast acreages of the environment have been

irreversibly destroyed. Post spill remediation measures adopted by the

operators of these pipelines have often failed to restore such

environments to pre-spill conditions.

32

7 Defect Assessment

Defect assessments (DA) are quantitative engineering evaluations that are

performed to demonstrate the structural integrity of an in-service component

that may contain a flaw or damage. The primary aim of DA is to detect,

locate, quantify, predict the residual life of the structure and arrest

progression of the damage. Damage assessment standard provides a rational

basis to determine whether or not a damaged component can continue to

operate until a replacement or repair programme can be implemented.

ASME B31.8 (2012) defines engineering assessment as a documented

assessment using engineering principles of the effect of relevant variables

upon service or integrity of a pipeline system and conducted by or under

supervision of a competent person with demonstrated understanding of and

experience in the application of engineering and risk management principles

related to the issue being assessed.

Defect assessment methods are required to determine the severity of defects

in pipelines in order to carry out repairs or replacements before they result

in failures. Defects occurring during the fabrication of a pipeline are usually

assessed against code compliant and proven quality assurance and control

through rigorous use of process and personnel qualification procedures such

as PQR and WPS. In spite of such controls, however, a pipeline will

inevitably experience some defects at some stage during its design life, thus

necessitating the need for assessment in order to determine whether or not to

repair the pipeline.

33

Defect assessment is usually a broad based multidisciplinary effort. A

typical defect assessment team would involve several engineering

disciplines in stress analysis, fracture mechanics, metallurgy/materials

engineering, corrosion, non-destructive examination, plant operations etc.,

because it requires collecting and analyzing crucial data from a number of

expert sources (Anderson, 2007). Defect Assessment may also involve

sophisticated computer simulations, including finite element analysis and

scomputational fluid dynamics in order to demonstrate that the equipment in

question is fit for continued service.

7.1 Design Code and Standard Requirements

7.1.1 Pipeline Defect Assessment Manual (PDAM)

Prior to the API 579-1/ASME FFS-1 (2007), a joint industry Pipeline Defect

Assessment Manual (PDAM) project sponsored by several pipeline holding

companies to produce a document specifying the best methods for assessing

defects in pipelines was issued in 2003. The PDAM provided the pipeline

industry with best practices for the assessment of a wide range of pipeline

defects in a detailed manual. It described the best method for assessing a

particular type of defect, the necessary input data, gives the limitations of

the method, and defines an appropriate factor to account for the model

uncertainty. The types of defects considered under PDAM are:

defect-free pipe

corrosion

gouges

34

plain dents

kinked dents

smooth dents on welds

smooth dents containing gouges

smooth dents containing other types of defects

manufacturing defects in the pipe body

girth weld defects

seam weld defects

cracking

environmental cracking

guidance on the treatment of the interaction between defects (leading

to a reduction in the burst strength), and the assessment of defects in

pipe fittings (pipework, fittings, elbows, etc.).

guidance on predicting the behaviour of defects upon failing,

including both leak or rupture, and fracture propagation.

The method utilizes internal pressure, external pressure, axial force and

bending moment or some combinations as the type of loading in the

development of the guidance.

A PDAM in the fitness-for-purpose assessment of a defect in a pipeline is

typified in Figure 4.

35

36

7.1.2 The API 579-1/ASME FFS-1 Standard

Prior to PDAM, damage assessments were undertaken by individual asset

holders and such efforts were thus non-standardized. In 2000 API published

the API 579 which later metamorphosed into the API 579-1/ASME FFS-1

in 2007 as a comprehensive guidance document for fitness-for-service

methodology for pressure equipment (pressure vessels, piping systems and

pipelines). It defines fitness-for-service as the ability to demonstrate the

structural integrity of an in-service component containing a damage or flaw.

This publication was intended to supplement industry codes by:

(i) ensuring safety of plant personnel and the public while older

equipment continues to operate;

(ii) providing technically sound fitness-for-service assessment procedures

to ensure that different service providers furnish consistent life

predictions; and

(iii) helping optimize maintenance and operation of existing facilities to

maintain the availability of older plants and enhance their long term

economic viability.

The assessment procedures could be used for fitness-for-service evaluation

and re-rating of pressure transmitting equipment designed and constructed

to the ASME and API codes and standards based on the present integrity of

the equipment given a current state of damage and the projected remaining

life. As illustrated in Figure 5, typically the procedure uses Levels 1, 2 and

3 and Failure Assessment Diagrams (FAD) as assessment techniques and

acceptance criteria.

37

38

For example, in order to determine if a crack may cause a structural failure,

the failure assessment diagram method uses two ratios: brittle fracture and

plastic collapse. The plastic collapse ratio is computed using the reference

stress, while the brittle fracture ratio is computed from the crack stress

intensity as illustrated in Figure 6. Where the stress intensity ratio/fracture

toughness (Kr) is plotted against the ratio of reference stress/yield stress (p

rL ).

Figure 6: Illustration of Failure Assessment Diagram

The scope of API 579/ASME FFS-1 covers assessment of:

existing equipment for brittle fracture

general metal loss

Metal loss due to corrosion / erosion (general, local, and pitting)

hydrogen blisters and hydrogen damage - HIC

weld misalignment and shell distortions

crack-like flaws

components operating in the creep range

fire damage

39

dents, gouges, and dent-gouge combinations

laminations

7.1.3 RSTRENG and the Modified B31G criteria

Other established methods include the RSTRENG (Remaining Strength) and

the Modified B31G criteria for assessment of corrosion flaws.

The method utilizes corrosion flaw model to assess, analyze, predict and

reduce or eliminate the corrosion risks facing a pipeline. Corrosion Damage

Assessment (CDA) for accurate measurement and characterization of the

corrosion defects is the most important stage of the prediction procedure.

ASME B31G code states that wall thinning in a pipeline due to corrosion or

erosion may be determined by a number of non-destructive examination

(NDE) techniques ranging from visual, radiographic, ultrasonic and other

methods of measurement. A number of NDE high resolution tools and

technique are for In-line Inspection (ILI) of the mechanical condition,

gathering of pipewall data and easy identification of corroded/eroded points

on a pipeline as discussed in Course PPE 801.1.

After the corrosion damage assessment the next step is to model the

geometry of the vicinity of the corroded sections. Mohitpour et al (2000)

has stated that the geometry of the vicinity of a corrosion flaw shape

approximated by the rectangular model or parabolic model is sufficient to

gain understanding of the corrosion interaction within that neighbourhood.

Figure 7 shows typical corroded points on a pipeline, while Figures 8 and 9

shows how the rectangular and parabolic models are derived.

40

Longitudinal Length, L

Fig. 7: Side View of a typical external corrosion defect

Longitudinal axis Maximum corrosion depth

rectangular model

Fig. 8: Rectangular Corrosion Model

Longitudinal axis Maximum corrosion depth

parabolic model

Fig. 9: Parabolic Corrosion Model

The two major mathematical models and their variants under this method

for predicting corrosion failures in pipelines [Mohitpour etal, 2000] are:

ASME B31G Criterion/RSTRENG Technique

The Surface Flaw Model

(i) ASME B31G Criterion/RSTRENG Technique

Under the ASME B31G procedure, the criterion for acceptability for a

corroded length in the model is given as:

corroded points

41

Lallow = DtB12.1

Where:

Lallow = Maximum allowable axial length of defect

B =

1

15.01.1

2

td

td

(8.1)

D = nominal outside diameter of the pipe, mm

t = nominal wall thickness of the pipe, mm

d = maximum defect depth of the corroded area, mm

d/t allowable in B31G is in the range of 0.1 d/t 0.8

The maximum allowable operating pressure (Pmaop) under the B31G is

defined to be less or equal to the maximum allowable design pressure, P.

The safe maximum pressure for the corroded area of the pipe is defined as:

13

21

3

21

1.1

2At

d

t

d

PPsafe for Psafe P and A 4 (8.2a)

t

dPPsafe 11.1 for Psafe P and A >4 (8.2b)

Where:

A = 0.893[L/ (Dt) ]

The maximum allowable defect depth, dallow is found by equating the

maximum safe operating pressure, Psafe to the maximum allowable

operating pressure (Pmaop) to obtain:

42

11.11

1.11

2

3

2AP

PP

P

td

maop

maop

allow for A 4 (8.3a)

P

Pd

maop

allow1.1

1 for A > 4 (8.3b)

As can be seen above, the ASME B31 relies on the theoretical design

pressure, P for determination of allowable defect depth due to corrosion.

Due to this strict over specification, the model is overly conservative and

serviceable pipelines are known to have been needlessly decommissioned

leading to waste (Mohitpour, 2000). In 1989, Kiefner et al introduced a

major improvement to reduce the conservatism in the B31G criterion.

Their improvement included new definitions and inclusion of the bulging

factor and the material flow stress, and a more detailed consideration of

the shape of the corrosion defect. This led to the RSTRENG procedure

which was initially released in 1989 and have since been further

enhanced. The basis of the RSTRENG procedure, which is iterative, is

the multiple evaluation of the predicted failure pressure based on an

affected area rather than the total area. Kiefner et al (1989) suggested that

an effective area based upon the maximum length, L and maximum depth

of pitting, d be used, such that the area in equations (8.3a) and (8.3b) will

be given as: A = 0.85 dL.

The modified B31G criteria as pointed out by Kiefner etal also proposed

a new failure pressure (Pf) based on a new Folias factor as follows:

43

Failure Pressure, (Pf) =

Mt

d

t

d

D

ty

85.01

85.0195.682

where:

242'

003375.0'

6275.01t

D

D

L

t

D

D

LM (8.4a)

for mmt

D

D

L50

'2

nominal bore

and

t

D

D

LM

2'

032.03.3 for mmt

D

D

L50

'2

(8.4b)

In spite of the modifications by Kiefner et al (1989) which eliminates

some of the conservatism in the criterion, however a number of

ambiguities still remain. For instance, when the corrosion is not

longitudinally oriented, the B31G will tend to underestimate the

remaining strength in the case of spiral corrosion. Also, when the

corrosion pits are closely spaced and where adjacent corrosion pits

interact, errors are introduced into the model. These limitations not

withstanding, it must be stated that for pipelines for oil and gas

transportation, the B31G model suffices since corrosion pits likely to

lead to failures usually need not be so complex due to the high fluid

transmission pressures involved in operating such pipelines. For

pipelines, where operating pressures are low such as municipal water

lines, the model proves to be overly conservative and may lead to

44

unnecessary maintenance interventions if the criterion is used for

corrosion failure prediction.

(ii) The Surface Flaw Model

The Battelle Memorial Institute and the American Gas Association

(Mohitpour et al, 2000) first developed the surface flaw model for

assessing failures in pipes with corrosion features in the early 70s. The

model was itself a modification of the ASME tangential hoop stress

equation incorporating a corrosion factor. In the simplified form it

states that the internal pressure at which a pipeline will fail, called the

Failure Pressure is defined as:

11

1

MA

A

A

A

R

StP

o

o

f

(8.5)

Where:

S = Strength measure of the pipe called the flow Stress (has been determined experimentally to be SMYS of the pipe, y + 68,950 kPa).

t = Pipe wall Thickness, mm

A = Area of metal removed, mm2

Ao = Original Area, mm2

M = The Folias correction factor

=

22

4

2'

2

2'

0135.0255.11tRRt

LL

for L 2R (8.6a)

=

Rt

L2

2'

61.11 for L > 2R (8.6b)

45

[The Folias factor is a stress concentration or shape factor that accounts for the

outward bulging that occurs in a thin-walled cylinder when subjected to internal

pressure].

R = Pipe Radius, mm

L = Maximum allowable length of the corroded point

projected on the longitudinal axis of the pipe, mm

= DtB12.1

=

5.0

2

115.01.1

12.1 Dttd

td

(8.6c)

D = nominal outside diameter of the pipe, mm = 2R

t = nominal wall thickness of the pipe, mm

d = defect depth of the corroded area, mm.

46

8. Introduction to Pipeline Engineering Critical Assessment

ASME B31.8 (2012) defines engineering critical assessment (ECA) as an

analytical procedure based upon fracture mechanics that allows

determination of the maximum tolerable sizes for imperfections, and

conducted by or under supervision of a competent person with demonstrated

understanding of and experience in the application of the engineering

principles related to the issue being assessed in order to prevent defects from

growing to critical sizes. It further states that ECA should also include

consideration for risk to the public, stress level, corrosion growth rate and

Maintenance and inspection methods.

For marine pipelines, engineering critical assessments are increasingly

becoming a routine part of pipeline design to determine tolerable flaw sizes

for pipeline systems in deeper water with increased loadings arising from

responses to thermal and hydrodynamic cyclic loading. Deep water

flowlines operating at high temperatures and pressures need to be designed

against problems such as significant end expansion/pipe walking and lateral

buckling (Olunloyo, 2007), since such pipelines are subject to large thermal

transients particularly during shut down. These thermal transients tend to

vary from ambient temperature and place a large fatigue demand on the

pipelines. The transients typically are very low frequency events with high

amplitudes, which could lead to lateral buckling. The loading rates

associated with the transients are very slow, hence the toughness properties

of the material in environments at low loading rates is important. The

pipelines are also subject to high stress and thus need to have good

47

toughness properties. Riser materials are also subject to significant fatigue

loading, though under conditions different from flow lines. They are

typically pre-loaded and operate under smaller amplitudes of loading and at

higher frequencies associated with wave motion.

Most welding fabrication codes specify maximum tolerable flaw sizes and

minimum tolerable Charpy energy, based on good workmanship, i.e. what

can reasonably be expected within normal working practices. These

requirements tend to be somewhat arbitrary, and failure to achieve them

does not necessarily mean that the structure is at risk of failure. An

Engineering Critical Assessment (ECA) is an analysis, based on fracture

mechanics principles, of whether or not a given flaw is safe from brittle

fracture, fatigue, creep or plastic collapse under specified loading

conditions.

ECA is often used to evaluate defects as it is less conservative than

traditional criteria and can reduce the reject rate of welds considerably. ECA

offers constructive guidance for qualifications such as flaw type, equipment

type, flaw detection uncertainties and flaw sizing

48

REFERENCES

Anderson T. L. (2007) Recent Advances In Fitness-For-Service Assessment

http://www.ndt.net/article/mendt2007/papers/anderson.pdf. Accessed in January, 2014.

American Petroleum Institute / The American Society of Mechanical Engineers (2007):

Fitness-For- Service. API 579-1/ASME FFS-1, 2nd

Ed., ASME Press, New York.

SME B31.8 (2012): Gas Transmission and Distribution Piping Systems, ASME Press,

New York.

ANSI/ASME (1995): Boler and Pressure Vessel Cod, Section II-Part A, ASME Press,

New York.

Bartholomew, R. D. and Shifler, D.A. (1996): Corrosion in Marks Standard Handbook

for Mechanical Engineers, Avallone, E. A. & Baumeister III, T. [eds.], 10th

edition,

McGraw-Hill, New York, pp.6.95 6.108.

BS 499 Part 1 (1991), Welding Terms and Symbols Part 1, Glossary for Welding,

Brazing and Thermal Cutting, The British Standards Institution, London.

Braestup, M.W., Andersesen, J.B., Andersen, L. W., Bryndum, M.B., Christensen C.J., Niels

Risho (2005): Design and Installation of Marine Pipelines, Blackwell Science Ltd., Fairfield,

N.J.

Cosham, A. and Hopkins, P. (2001), A New Industry Document Detailing Best

Practices In Pipeline Defect Assessment, Proceedings of the Fifth International Onshore

Pipeline Conference, Retrieved from: http://www.penspenintegrity.com/downloads/virtual-

library/industry-best-practice.pdf . Accessed in January, 2014.

Crocket, P.A. and Maguire, R. (1999), Pipeline Failure Management, IMech Conference

Transactions on Ageing Pipelines, Paper C571/009/99, Professional Engineering Publishing

Limited, London, pp. 39-48.

Douglas, J.F., Gasiorek J. M., Swaffield J.A. and Jack, B. L.(2005), Fluid Mechanics, 5th

ed., Pearson Education Limited, Essex, England.

Etube, L.S. (2001), Fatigue and Fracture Mechanics of Offshore Structures, Professional

Engineering Publishing Limited, London.

Kiefner, J.F., Bruce W.A. and Stephens, D.R. (1994): Pipeline Repair Manual, Final Report

to A.G.A. Line Pipe Research Supervisory Committee, Houston, Texas.

49

Kiefner, J.F. and Vieth, P.H. (1989): When Does a Pipeline Need Revalidation? The

Influence of Defect Growth Rates and Inspection Criteria on Operators Maintenance

Program, in Pipeline Rules of the Thumb, McAllister, E.W. (Ed.), Gulf Publishing

Company, Book Division, Houston, Texas, pp. 555 -566.

Larock, B. E., Jeppson, R.W. and Watters, G. Z. (2000), Hydraulics of Pipeline

Systems, CRC Press LLC, Boca Raton, Florida 33431. http:www.engbag.org/files/70d5115116b163f8aaf4_Hydraulics%20of%20Pipeline%20System san. Accessed February, 2015.

McAllister E.W. (Ed.) (2000), Pipeline Rules of the Thumb Handbook, 2nd

edition, Gulf

Publishing Company, Book Division, Houston, Texas.

Mohitpour, M., Golshan, H. and Murray, A. (2000), Pipeline Design & Construction A

Practical Approach, ASME Press, New York.

NACE International (1999), Pipeline Corrosion, Conference Transactions on Corrosion

Detection Using Intelligent Pigs, Corrosion Information Compilation Series, National

Association of Corrosion Engineers, Houston, Texas Houston, Texas.

Olunloyo O.S. Vincent, Oyediran A. Ayo, Adewale Ajayi, Adelaja O. Adekunle & Charles

A. Osheku (2007), Concerning the Transverse and Longitudinal Vibrations of a fluid

Conveying Beam and the Pipe Walking Phenomenon, Final Paper No. OMAE200729304,

The 26th

International Conferenc on Offshore Mechanic and Arctic Engineerng, San

Diego, USA, 10-15 June 2007.

Rajput, R. K. (2008), A Textbook of Fluid Mechanics and Hydraulic Machines, S. Chand &

Company Ltd., New Delhi.

Roylance David (2001): Introduction to Fracture Mechanics, Retrieved from:

http://ocw.mit.edu/NR/rdonlyres/Materials-Science-and-Engineering/3-11Mechanics-of-

MaterialsFall1999/F34792CC-7AA5-47F0-81AD-13664B5F856C/0/frac.pdf. Accessed

February, 2009.

Wintle, J.B. editor (2000): Flaw Assessment in Pressure Equipment and Welded Structures,

Professional Engineering Publishing Limited, London.

50

APPENDIX I

GLOSSARY OF TERMS AND DEFINITIONS

Anomaly: An indication, generated by non-destructive examination of an

irregularity or deviation from sound weld or base parent pipe material, which

may or may not be an actual flaw.

Buckle: A partial collapse of the pipe due to excessive bending sharp internal

diameter reduction.

Construction Defect: Feature that arises during the construction of the

pipeline, including a girth weld anomaly, arc strike and grinding.

Corrosion: Corrosion is the deterioration of a material as a result of reaction

with its environment, especially with oxygen. It is the disintegration of metal

through an unintentional chemical or electrochemical action. It is a

destructive chemical process; most often applied to the conversion of a metal

to one of its compounds, for example, the corrosion of iron by oxygen and

water to produce iron oxides (rust).

Crack: a stress-induced separation of the metal which, without any other

influence, is insufficient in extent to cause complete rupture of the material.

Dent: distortion of the pipe wall resulting in change of internal diameter but

not necessarily resulting in localized reduction of wall thickness.

Flaw: also called a defect or feature, an anomaly which may have a

deleterious effect on the structural integrity of the pipeline and consequently

its ability to contain or transmit internal pressure.

Girth Weld: a complete circumferential butt weld joining pipe or

components.

Gouge: mechanical induced metal loss which causes localized elongated

grooves or cavities.

Hole: where the hydrocarbon are released in diameter of defect exceeding

2cm and equal or less than the diameter of the pipe.

Intelligent Pig: an inspection tool equipped with electronic sensors which

can perform a non-destructive examination.

Metal Loss Defect: An area of pipe wall with a measurable reduction in wall

thickness.

51

Mill Defect: A defect that arises during manufacture of the pipe, for instance

a lap, silver, lamination, non-metallic inclusion, roll weld and seam welded

anomaly.

Nominal Pipe Size (NPS): is a dimensionless designator of pipe. It indicates

a standard pipe size when followed by the appropriate number (e.g. NPS 12

means a 12 pipe).

Nominal Outside Diameter: is the as-produced or as-specified outside

diameter of the pipe and may or may not be the same as the NPS (e.g. a

standard NPS 8 pipe has a specified nominal diameter of 8.625

(219.08mm), while an NPS24 pipe has 24.000 (609.60mm) nominal

diameter.

Nominal Wall Thickness: is the wall thickness computed from the nominal

OD of the pipe, subject to tolerances and mathematically satisfying: t = tp+ A

[where tp is the pressure design wall thickness and A are the allowances

added for threading, grooving or corrosion or an increase if used as a

protective measure].

Pipeline: a pipeline transmission system is an assembly of line pipes

continuously strung together by welding (or other such means of joining) and

devices such as pumps, compressors, valves, swivels, meters, manifolds etc.

for transportation of a fluid (even solids!) from one point to another.

Interstate, large bore types longer than 100km are usually called cross

country pipelines. Pipelines are generally classed as part of a nations

infrastructures akin to rail, roads etc.

Pipeline Failure: an unintentional release of process fluids from a pipeline

transmission system into the surrounding environment.

Rupture: where the release of pipeline contents escapes from a defect

diameter which is more than the pipe diameter.

Specified Minimum Yield Strength or Stress (SMYS): a required strength

level that the measured yield stress of a pipe material must exceed, which is a

function of pipe grade. The measured yield stress is the tensile stress required

to produce a total elongation of 0.5 percent of a gage length as determined by

an extensometer during a tensile test.

52

Steel Pipes: alloys of predominantly iron and carbon and other measurable

elements - manganese, phosphorus, sulphur etc. Carbon steel derive its

distinctive properties from carbon, while alloy steels owe their properties to

carbon, as well as other elements such as nickel, silicon, chromium.

Weld Defect: defect in the welded joint of a pipeline.