Computer Aided Design (CAD) for Failure Analysis in a Crude Oil and Gas Carbon Flow line

American Journal of Engineering Research (AJER)

2015

American Journal of Engineering Research (AJER) e-ISSN: 2320-0847 p-ISSN : 2320-0936 Volume-4, Issue-8, pp-64-74 www.ajer.org Research Paper

Open Access

Computer Aided Design (CAD) for Failure Analysis in a Crude Oil and Gas Carbon Flow line ALAO Kehinde T. 1, OLALERE Olusegun A.2,ADEYI Oladayo3, OLADAPO Micheal A.4 1, 4

(Department of Mechanical Engineering, Ladoke Akintola University of Technology, Ogbomoso, Nigeria.)

2 (Department of Industrial & Production Engineering, University of Ibadan, Oyo State, Nigeria) 3 (Department of Chemical Engineering. Landmark University Omu-Aran, Kwara State, Nigeria)

ABSTRACT: The failure analysis in flow lines comes to relevance in order to prevent the menace attached to failures; financial losses, dangers to workers, and production breakdowns. Hence the materials used must be of good mechanical properties, low cost and of wider availability.

The pressure distribution and stress analysis were estimated by varying the diameter and pressure drop in the pipe. These were subsequently obtained from a set of mathematical models computed and displayed through the use of a simulated computer aided design auto inventor-based software.

The results obtained from the Computer aided design showed the stress induced in pipe during failure. By varying pressure the maximum operating pressures increases at constant diameter of pipe, with a corresponding increase in pipe stress. It also shows the rate at which liquid flow through the pipe at varying maximum operating pressures and diameter together. From result obtained also, the wall thickness of the pipe should not be less than 0.25 inch (6.35mm) This study helps to analyze oil pipeline failures in Nigeria with the aim to undertake a desk study to evaluate the procedures for maintenance and contingency plans for addressing oil pipeline failures in Nigeria.

Keywords:Crude oil, computer-aided-design (CAD), failure analysis, pipeline (flow line), pressure drop I.

INTRODUCTION

The failure of components and materials of most machines and machineries is one of the most dreaded situations in any producing establishment due to the buoyant nature of the study. Hence there is a need for a proper monitoring with utmost scrutiny in the design and production of pipes/flow lines used in oil and gas industry in order to prevent distortion in oil and gas production. Distortion in production as regards piping is generally induced by the failure of these pipes meeting up with proper design codes and criteria. They are therefore said to be failing or to have failed, depending on the severity or discrepancy from design criteria before the ultimate mode of failure-rupture. Pipelines are commonly made of carbon steels due their good mechanical properties, low cost and wider availability. However, in spite of good properties exhibited by carbon pipes, their resistance to corrosion is relatively low. Normally, as an oil well ages, the production of oil starts to decline whereas water and gas flow rates tend to increase. The presence of high corrosive agents such as CO 2, H2S and chlorine compounds dissolved in the fluids can therefore accelerate corrosion process inside the pipeline. Hence, the impact of changes in fluid composition on a pipeline should be anticipated during maintenance program. Oil leaks have been recently reported to occur at a horizontal crude oil subsea pipeline after 27 years in service. During operation, crude oil was pumped from subsea wells into the horizontal pipeline and crude oil was then flowed out from the pipeline directly into a long radius elbow section which turned the crude oil flow vertically allowing the flow to pass through a riser for further processing in the platform [1].

Hence, failure analysis comes to relevance in order to prevent the menace attached to these fractures, financial losses, dangers to workers and personnel, production breakdowns and also the likelihood to spark up an epidemic. Failure analysis and design helps to maintain and give the piping systems drawing a predictive forecast and thus a preventive maintenance strategy against possible causes of failures such as corrosion, sand

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2015

erosion (depleting thickness of pipes from the inside), excessive stress in pipes, fluctuating pressure effects, fatigue etc. These effects have posed perennial difficulties to the oil and gas industry, hence the untiring efforts to always find new, workable techniques and methods into analyzing the flow line to designing possible solutions.Furthermore, the enormous dividends generated from the oil and gas industry has helped put more concern into the close monitoring of the pipe’s efficiency over a good period of time and thus reducing possible hazards to a barest minimum. This research work will be encompassing; evaluation of crude oil flow parameters such as pipe thickness, working pressure, oil flow pressure, temperature, stresses in pipes etc. and their relation to each other using the carbon steel pipe alone as our case study.

II LITERATURE REVIEW 2.1

Preamble Major pipelines across the world transport large quantities of crude oil, natural gas, and petroleum products. These pipelines play a crucial role in providing needed fuels for sustaining vital functions such as power generation, heating supply, and transportation. However, due to the hazardous properties of these products transmitted, a ruptured pipeline presage serious environmental problems. This problem is further compounded by the fact that many developing countries have not yet established proper guidelines and standards for the design, construction, and operation of major oil pipelines. This study helps to analyze oil pipeline failures in Nigeria with the aim to undertake a desk study to evaluate the procedures for its maintenance and contingency plans for addressing oil pipeline failures in Nigeria. The risk associated with pipeline in terms of safety of people, damage to the environment and loss of income has been a major concern to pipeline integrity managers. Agbaeze (2000) mentioned his view on how to improve pipeline Integrity Management, opining that pipeline operators can realize many benefits by implementing a data integration approach that will enables integrity managers, risk assessment specialists and pigging engineers to view and analyze combined information from disparate surveys and to increase the value of data by shaving it across the entire corporation [2].

There have been a number of studies conducted by researchers on causes of oil pipeline failures in the oil and gas industry. Ikporukpo and Chris, (1998) examined the causes of pipeline leaks versus pipeline ruptures and the proportion for each. In failures resulting in product loss, leaks constituted 86.8 % of failures and ruptures 13.2 %. Corrosion is the predominant cause of leaks. According to his findings, third party damage is the leading cause of line ruptures. Since 1994, 191 hits were recorded, and these are not included as they did not result in either leaks or ruptures. The hits equaled 47 % of all recorded third-party incidents for the years 1994-1997, demonstrating that approximately half of all third party incidents resulted in a pipeline failure.

Reference showed that about 50 % of third-party incidents resulted in loss of pipeline products [3]. The number of internal corrosion failures for multiphase pipelines and discovered that internal corrosion failures increased steadily while the number of external corrosion failures held steady. They stated for sour gas pipelines, internal corrosion is the major cause of failure [4]. External corrosion failures have declined in recent years, possibly as the result of improved coatings and increased inspection. Of the sour line failures, about 86 % were leaks and 14 % were ruptures. They used the latest technology in the fields of internal electronic inspection, metallurgy, coatings, cathodic protection, and chemical inhibition. Nwankwo et al., (2012) and Odusola (2012) extensively studied the effects of internal corrosion failures for natural gas pipelines which have generally been increasing.

Some "other" category which include high vapour pressure liquids, low vapour pressure liquids, fuel gas, and all others showed failure rates to be relatively few and the causes to be relatively random. Ilman (2014) worked on subsea crude oil steel pipeline oil leakage whose failure was caused by electrochemical corrosion combined with mechanical process known as flow induced corrosion [1].

2.2 Flow of crude oil and causes of leaks and ruptures in flow lines Oil pipelines transport liquid petroleum products from one point to another. There are generally three types of oil pipelines:  Gathering lines: travel short distances, collect unprocessed oil products from wells and deliver them to oil storage tanks. Pipes range from 4 to 12 inches in diameter  Feeder lines:move product from oil storage tanks and processing plants to the transmission pipelines.

They are generally bigger than gathering lines, but smaller than transmission lines.  Transmission lines:can be up to 48 inches in diameter and transport oil and associated products from producing to consuming areas, including across provincial and international boundaries. The oil is piped to refineries where it is refined into petroleum products.

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Source: Amec Paragon, (2013) Figure 1: Represent the flow line, gathering line and the transmission line Internal corrosion, external corrosion, external intervention (for example: hit by a truck or back-hoe), soil displacement such as landslides, material defects, and system malfunctions (for example: operating over design pressure) can cause leaks and ruptures. Based on incidents reported to the National Energy Board (2010), the majority of leaks are related to pump stations and valves, rather than the body of the pipeline. In general, corrosion accounts for about 20% to 30% of pipeline leaks.

2.3

Failure Analysis The flow line itself can be classified to be a pressure vessel in that it works under certain service pressure requirement and hence a vessel because it is enclosed and used as a leak proof transport medium from one end to another. Vessel failures can be grouped into four categories which describe why a vessel failure occurs; failure can also be grouped into types of failures, which describe how the failure occurs. Each failure has a why and how to its history. It may have failed through corrosion fatigue or because the wrong material was selected. The different Categories of Failures were analyzed by Ilman and Kusmono (2014).  Failure due to material: Selection of flow line materials is important so as to prevent reaction of the hydrocarbon element with the internal surface of the flow line thus, preventing corrosion and to be able to withstand other external factors. When selecting material, consideration must be given to materials with good market availability, documented fabrication, service performance, operating condition, corrosion monitoring possibilities and compatibility to other materials to be used.  Failure due to design: For the design of a pipeline, the overall thickness, addition of intermediate leak proof sheath, increasing the moment of inertia to withstand pressure and also selecting cathodic protection system design to prevent corrosion etc to make the overall flowline last longer.  Failure due to fabrication: When fabricating, favourable combination of weldability, strength, corrosion resistance together with the condition of the environment in which the pipeline will be installed must be carefully considered. Also, when fabricating, the material must be subjected to pressure testing to detect failures related to welding, strength etc.  Failure due to service: Regularly scheduled inspections, evaluations and testing by qualified personnel are critical part of preventing failure. Their purpose is to prevent, predict and readily detect discharges/leakages. So active and regular service check must be done on this flow line to prevent failure.

III RESERCH METHOD AND MATERIAL The research work involved a full understanding of what failure is all about. To this effect there is the need to have an overview of the root cause of failure, the methods used in this study involves the following; 1. Library and online research 2. Questionnaire survey 3. Oral interview 4. Physical observation and mathematical model 5. Computer Aided Design 3.1 Field Survey In order to examine the root cause of failure, several cases of failure that have occurred were critically looked into. Selected team of field workers, inspection officers were posed with questions based on failure in flow lines.

Some of the questions asked are highlighted below.

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How long was the part in service?

What was the nature of the stresses at time of failure?

Was the part subjected to an overload?

Was the part properly installed?

Was it subjected to service abuse?

Were there any changes in the environment?

Was the part properly maintained?

What was the service/ normal pressure of the crude oil coming from the well and going out of the well?

How and where did the failure occur?

What is the primary cause of the failure (lack): corrosion, dent, human sabotage inadequate service demand etc?

What existing failure analysis instrumentation do they have or work with?



Field testing permitted the evaluation of the effects of materials, design and fabrication variables on performance of the under-controlled conditions, by combining the information from tests with the results from analysis; a clear picture of the causes of failure was obtained.

While studying failure, care was taken to avoid destroying important evidence. Detailed studies usually require documentation of service history (time, temperature loading environment etc) along with chemical analysis, photomicrographs and the likes.

3.2 Computer Aided Design (CAD) Use of computer programme C++ and Auto Inventor was extensively used in this project work. C ++ was used to analyze data gotten from industry to give a better operating pressure with a perfect diameter and to monitor the pressure drop along the pipeline. The solid work design shows the effect of stress caused on the pipe due to variation of operating pressure and diameter of the pipe.

3.3. Mathematical model for stress analysis through computational method` The flowline thickness varies from different sections to another due to variation in pressure and temperature.

The thickness of the flow line from the well to the flow station and finally to the refinery or terminals must not be minimum to the one needed for a specified pressure and temperature.

PD C 2( SE  Py )

tm 

(1)

Where, tm= Minimum flow line wall thickness (in) allowable on inspection P=Maximum internal service pressure gauge (1b/in2) D=Outside diameter of pipe (in) S=Maximum allowable stress in material due to internal pressure (1b/in2) ) E=Quality factor Y=A coefficient, values for which is in the standard code C=Allowance for threading mechanical strength and corrosion (in) with values listed in the standard code.

3.3.1 Stresses in Members The stresses in members are shown in equations (2) and (3) below. đ??š

đ?‘†đ?‘š = đ??´đ?‘š

đ?‘š

đ??žđ?‘š

đ?‘†đ?‘š đ??´đ?‘š đ?‘ˆđ?‘š

(2) (3)

Where,

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Km= spring constant of member Fm= tensile force in the bolt S Um= the amount by which the member is extended when it is loaded from zero to f m Sm=Stress in member Am=Area of the member 3.3.2 Pressure drop in pipelines The pressure drop in pipe, due to friction is a function of the fluid flow-rate, fluid density and viscosity, pipe diameter, pipe surface roughness and the length of the pipe. It can be calculated using the following equation below đ?œŒđ?‘˘ ² ΔPf = 8f ( đ??ż đ?‘‘đ?‘– ) (4) 2 ΔPf = Pressure drop, N/m2 f = Friction factor L = Pipe length, m di = Pipe inside diameter, m đ??† = fluid density, Kg/m3 u = fluid velocity, m/s

IV RESULT AND ANALYSIS 4.1

Data Presentation For an effective assessment of the failure in flowline, a computer software progamme was written using C++, and values were generated for the analysis. These programmes were used to implement the sets of equations that were supplied. Data generated were analyzed and a design simulation was shown using AutoCAD inventor. Hence, applicable/workable failure indices were obtained, practical enough to predict the possible period which failure may occur, conditions under which it may occur and period of tolerance before the ultimate mode of failure rupture.

4.2

Parameter values The following data were collected from various oil fields/oil companies within the country. These data are those analyzed and results presented in subsequent sections.

Table 1: Data of Parameter Values from Oil Field Type of system Hazardous liquid Accident type: Pipe failure and leak Material release: Crude oil API 35.6º Maximum operating pressure (MOP) Outside diameter of pipe (D) Specified minimum yield strength (S) Normal wall thickness of pipe (T) Design factor (quality factor E) (F) Maximum depth of corroded area (C) Pit depth percentage (C/t) Constant for maximum allowable Pressure (G) Safe maximum (derated) pressure for corroded area (Pd) Fluid velocity(U) Friction factor (f) Year in Service period of pipe is between (1993 – 2001)

Value

Units

800 12.750 42,000 0.25 0.72 0.080 32.0 3.003 11,100 0.4 0.07 6

Psi In Psi In In % Psi m/s Âľ Years

Source: ICPI, Abuja (2012) From the data provided

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4.3 Calculations and Analysis Using stress analysis through computational method Using equation 3. And analyzing the data through C ++ application t m=

đ?‘ƒđ??ˇ 2 đ?‘†đ??¸+đ?‘ƒđ?‘Œ

+C

(5)

Making S the subject of the formular; S=

đ?‘ƒđ??ˇâˆ’2đ?‘ƒđ?‘Œ(đ?‘Ąđ?‘š −đ??ś) 2đ??¸ đ?‘Ąm−đ??ś

(6)

MOP P = 800 Psi

D = 12.750 in tm = 0.250 in E = from the data table(F – Design factor) = 0.72 Y = 0.4 C = 0.080 Calculation from our C++ application shows the amount of stress exacted on the pipe during the time of failure as 41222.22ib/in2

Plate 1: C++ programmed showing the calculation of stress exacted on the pipe at 800 psi

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The analyzes of the stress induced in the pipe by varying both pressure and diameter at a constant maximum operating Pressure of 800 Psi is given in table 2 below.

Table 2: Results Generated at Constant pressure and varying pressures and diameters MOP Diameter of pipe (in) Stress induced in the pipe (ib/in2) 800

9

28967.3202

800

10

32235.2941

800

11

35503.2679

800

12

38771.2418

800

12.75

41222.2222

Table 3: Results Generated at a constant diameter of 11 inch MOP Diameter of pipe (in) Stress induced in the pipe (ib/in2) 700

11

31065.3594

750

11

33284.3137

800

11

35503.2679

850

11

37722.2222

900

11

39941.1764

Table 4: Results Generated at a constant diameter of 12 inch MOP Diameter of pipe (in)

Stress induced in the pipe (ib/in2)

700

12

33924.8366

750

12

36348.0392

800

12

38771.2418

850

12

41194.4444

900

12

43617.6471

Table 5: Results Generated At a constant diameter of 12.75 inch MOP

Diameter of pipe (in)

Stress induced in the pipe (ib/in2)

700

12.75

36069.4444

750

12.75

38645.8333

800

12.75

41222.2222

850

12.75

43798.6111

900

12.75

46375.0000

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American Journal of Engineering Research (AJER) 50000 40000

36069.4444

38645.8333

41222.2222

43798.6111

2015

46375

30000

MOP

20000

Diameter of pipe (in) Stress induced in pipe (ib/in²)

10000

1

2

3

900 12.75

850 12.75

800 12.75

750 12.75

700 12.75

0

4

5

Figure 2: Stress induced in a pipe of diameter 12.75 inch and MOP of 700 Psi – 900 Psi 45000 40000 35000 30000 25000 20000 15000 10000 5000 0

31065.3594

33284.3137

35503.2679

37722.2222

39941.1764

MOP Diameter of pipe (in) Stress induced in pipe (ib/in²)

1

2

3

900 11

850 11

800 11

750 11

700 11

4

5

Figure 3: Stress induced in a pipe of diameter 11 inch and MOP of 700 Psi – 900 Psi

50000 40000 33924.8366

30000

36348.0392

38771.2418

41194.4444

43617.6471

MOP Diameter of pipe (in)

20000

Stress induced in pipe (ib/in²) 10000

1

2

3

900 12

850 12

800 12

750 12

700 12

0

4

5

Figure 4: Stress induced at a constant diameter of 12 inch and MOP of 700 Psi – 900 Psi.

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Plate 6: Simulation of the effect of pressure at 6.2052 MPa (900 psi) on an 11 inch pipe

4.4

Pressure drop calculation

Using equation 3.6 and using the C++ application đ?œŒđ?‘˘ ²

ΔPf = 8f ( đ??ż đ?‘‘đ?‘– )

(7)

2

f = 0.07 Âľs L = 1000m (1Km) di = 10.25 in đ??† = 847 for API 35.6 u = 0.4 m/s The pressure that will be drop in the pipe in a distance of 1000m/1km will be 21.11 psi, therefore at about 38 km at most, there should be a pressure booster in place to increase the pressure back to the maximum operating pressure. Plate 7 shows the pressure drop calculation from the C ++ programme.

Plate 7: C++ Programme showing the pressure drops in a pipeline

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V. DISCUSSION From the computer aided design (CAD) of the stress induced during failure, results were obtained by varying both the pressure and diameter shows that at constant maximum operating pressure, the diameter of the pipe diameter increases due to the density of the liquid stress induced. Hence, at constant diameter of 11 inch (279 mm), 12 inch (305 mm), and 12.75 inch (324 mm), the higher the maximum operating pressure, the higher the stress induced in the pipe.

The figure 2 shows the graphical representation of the stress induced between a diameters of 9inch-12inch at constant maximum operating pressure of 800 psi (5.5158 Mpa) while figure 4.3 is the graphical representation of stress induced at a constant diameter of 12inches and a maximum operating pressure of 700 psi (4.8263 Mpa) - 900 psi (6.2052 Mpa). However, this varies the rate of stress difference at separate maximum operating pressure value with graphical authentications.

The rate at which liquid flow through the pipe at varying maximum operating pressures and the representation of stress induced at a constant diameter of 12.75 inches and maximum operating pressure of 700 psi – 900 psi were illustrated in figure 5.

The Plate 2 and 3 shows the simulation of the effect of pressure at 800 psi (5.5158 Mpa) on a 10 and 12 inch pipe. This was extracted from the auto desk inventor, showing the increment of the pressure distribution in the pipe. The design showed the pressure distribution in the 10 inch pipe and 12 inch pipe. For the 12 inch pipe, the pipe experiences much pressure at the opening and edge. And plate 4, 5, and 6 show the simulation of the effect of 700 psi, 800 psi and 900 psi on a pipe of 11inch diameter. It shows the pressure distribution in the pipe and also shows that stress is much concentrated at the edge/opening of the pipe.

VI. CONCLUSION The pressure distribution and stress analysis were estimated by varying the diameter and pressure drop in the pipe. These were subsequently obtained from a set of mathematical models computed and displayed through the use of simulated computer aided design auto inventor-based software.

The computer aided design showed the effect of the data analyzed (pressure and diameter) on the pipe and also showed the overall effect on the pipe through simulation of the parameters given.

A level of dependence were obtained from the model and the results revealed their corresponding stress according to the given operating parameters. Furthermore, it was authentically observed that at a pressure of 800 psi (5.5158 Mpa), the 10 inch (254 mm) -11 inch (279 mm) diameter pipe will be the most suitable for use, due to the pressure distribution observed through the Auto Inventor design software.

Therefore, this study can be successfully employed in the selection of pipelines as it is interchangeably used in this research work, as well as for other types of pipe specifically for crude oil, as long as the fluid properties for the type of fluid to be carried and operating parameters are known. This study helps to analyze oil pipeline failures in Nigeria with the aim to undertake a desk study to evaluate the procedures for its maintenance and contingency plans for addressing oil pipeline failures in Nigeria

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