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SCHOOL OF CIVIL, ENVIRONMENTAL & CHEMICAL ENGINEERING
PROC 2076: Chemical Engineering Design Assignment 2: Oil & Gas Pipeline Material Selection Group 3 17 September 2015 Dr. Liam Ward Group Members: Farihin Afini Abdul Muthalib Fatin Hanisah Mohd Anuwi Sharifah Nurfasha Syed Idris Shuhada Atika Idrus Saidi Wan Lily Aisyah Mazlan
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1 EXECUTIVE SUMMARY The main idea and the scope of this report is on the process of material selection and designing an oil and gas pipeline system for distribution purposes. Out of a few different types of oil and gas pipeline exist, natural gas distribution pipeline is chosen. Natural gas is delivered via distribution pipelines domestically, industrially, or even agriculturally. Different types of corrosion in underground environment exists where underground pipelines are installed including general corrosion, pitting corrosion, stress-corrosion cracking (SCC), and differential corrosion cells. Meanwhile, differential aeration cell and galvanic corrosion are another two types different corrosion classified under the differential corrosion cells where oxidation and reduction occur separately. The specific function and a few functional requirements are listed first before introducing the design concept of natural gas distribution pipeline. A shortlist of suitable materials for use as construction of the pipeline based upon the major requirements is provided. The materials involved are steel, copper, polyethylene, and fiberglass while the discounted material are cast and wrought iron. The four materials are ranked according to a few factors affecting the choice of materials which are corrosion-resistant, maximum service temperature, toughness and cost of materials. From the rank and index mentioned before, the best materials are then selected based upon the degree of resistance to corrosion required for the design. A critical analysis is done based upon the materials ability to meet the requirements for the system. The focus is on combating exterior corrosion since there is not much issue with internal corrosion due to the contents of the natural gas passing through. Polyethylene is finally chosen as the most suitable material to resist corrosion from the surrounding underground environment while carbon steel is selected as the type of interior pipe. Other factors affecting the choice of materials for the construction of pipelines that could be taken into account are weldability and joining, environmental factor, availability of materials, maintenance, and miscellaneous shock factors. Several possible improvements that will allow the distribution line to work at its optimum efficiency are suggested such as consideration for internal coating, materials’ grades, and accuracy in calculation. Conclusively, carbon steel and polyethylene are chosen to construct the interior and exterior of natural gas distribution pipeline respectively as they match well with the five main operating parameters of material selection.
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2 TABLE OF CONTENTS 1
Executive Summary ............................................................................................................ 2
3
List of Figures and Tables ................................................................................................... 4
4
Introduction ......................................................................................................................... 5
5
Literature Review ................................................................................................................ 6
6
Specific function and functional requirements ..................................................................... 7
7
Design concept ................................................................................................................... 8
8
List of suitable materials...................................................................................................... 9 8.1
Materials for analysis ................................................................................................... 9
8.2
Discounted materials ................................................................................................... 9
9
Suitability of materials: Rank and index of materials ..........................................................10
10
Selected materials ..........................................................................................................12
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Other factors affecting choice of materials ......................................................................13
11.1
Weldability and joining ................................................................................................13
11.2
Environmental factor ...................................................................................................13
11.3
Availability of materials ...............................................................................................13
11.4
Maintenance ...............................................................................................................13
11.5
Miscellaneous shock factors .......................................................................................13
12
Possible improvement ....................................................................................................14
13
Conclusion and recommendations..................................................................................15
14
References ....................................................................................................................16
15
Appendix ........................................................................................................................17
15.1
Peer Review ...............................................................................................................18
15.2
Material selection charts .............................................................................................19
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3 LIST OF FIGURES AND TABLES Figure 1: Simple design concept where 1 – internal surface, 2 – external surface Table 1: Corrosion-resistant classification for considered materials Table 2: Range of maximum service temperature for considered materials Table 3: Toughness for the considered materials Table 4: Cost for considered materials per kilogram
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4 INTRODUCTION Oil and gas pipelines are needed for safe and efficient transportation of large quantity of oil and gas for instance crude oil and natural gas. The delivery network for this transportation consists of many types of pipelines, each serving its purposes. In general, pipelines can be considered as cost-effective alternative options apart from using tanker truck loads and rail cars. Pipelines need impressively less energy to function than operating trucks or rail. This is due to the fact that pipelines have much lower carbon footprints count. Underground pipelines are one of the many safer way for oil and gas transport. From the numerous types of pipelines, this report will mainly be focusing on the natural gas distribution pipelines. Natural gas is a hydrocarbon compound which consists of hydrogen and carbon atoms. The simplest form of natural gas is methane gas which is made up of one carbon atom bonded to four hydrogen atoms. Gaseous hydrocarbon includes compounds with lesser amount of natural gas liquids, and other gas such as nitrogen, carbon dioxide, hydrogen sulfide, or even water. These trace compounds will be discarded at gas processing facilities once they are produced. The natural gas which flows along the pipelines will be distributed domestically, industrially, and agriculturally. The outer diameter of pipeline can be as small as ½ inch to 24 inch while the length depends on how far the natural gas will be distributed to. The natural gas delivery network starts at the producing wellheads, where products will go through a gathering lines to a compressor station. From this compressor station, the unrefined natural gas will either go to the underground storage through transmission lines, or to a processing plant, where the gas is further refined and compressed before getting delivered to city gates or local distribution companies. Through distribution lines, refined gas is then supplied to commercial or residential customers. The gathering of raw natural gas is done by the small diameter pipes from producing well. It is then transferred to a gas processing facility. This can also be applied to water, impurities, and other gases. Natural gas is said to be moving at speeds up to 40 km/h through these pipelines (Canadian Energy Pipeline Association, 2015). Back in the days, pipelines were made from hollowed-out logs, lead and copper. Now as the technology improves, they are made from high quality steel. The scope of this report is to design an improvised version of line-pipe system for distribution purposes. The main objective is to provide justification for the groups or classifications of materials that are selected based upon the line-pipe design requirements and the ability of the materials to meet these requirements. The specific function and functional requirements for natural gas distribution lines are listed thus a simple design concept is outlined. A few suitable materials for use as construction of the pipeline based upon the major requirements are shortlisted. The materials are next ranked in terms of suitability and meeting the operating requirements. Three materials that have been shortlisted are then selected based upon the degree of resistance to corrosion required for the design. A detailed analysis is also provided based upon the materials ability to meet the corrosion requirements for the system under consideration and importance of corrosion resistance compared with other requirements for final selection of material for construction. Other factors affecting choice of material such as cost, availability of materials, processing, welding, joining, etc. are discussed thoroughly. Some possible improvements that can be made to the pipeline design are suggested.
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5 LITERATURE REVIEW The main aspect of material selection for this assignment is on corrosion, thus this literature review will cover the different types of corrosion in underground environment where underground pipelines are installed. In United States, from 1994 until 1999, it was recorded that many accidents happened under the case of natural gas transmission pipeline and natural gas distribution pipeline due to the hazardous liquid in the pipelines which the main factors of its existence are caused by corrosion, internal and external (US Department of Transportation, 2015). According to American Society of Metals International (2002), the types of corrosions in the underground environment for pipeline installation are general corrosion, pitting corrosion, and stress-corrosion cracking (SCC). Another type of corrosion that is most affect the underground pipelines is the differential corrosion cells. The most common morphology of the differential corrosion cells is uneven metal loss over localized areas covering a few to several hundred square inches. The basic mechanism in corrosion is redox reaction, where they occur physically at or near the same location on a metal. Oxidation and reduction reaction always occur at the same moment. However, as its name, differential corrosion cells, the oxidation and reduction reaction occur separately on the metal surface, where the oxidation occur at one side and reduction occur at the other side of the metal. In addition, under differential corrosion cell, a variety of different types exist. They are differential aeration cell and galvanic corrosion. Differential aeration cell happens when different parts of a pipe are exposed to different concentration of oxygen in soil, and cells created by differences in the nature of the pipe surface or the soil quality. Meanwhile, galvanic corrosion occurs when potential difference in the flow of electrical current is created by the presence of different metals. This is because different metals have a different corrosion potential in a given environment. In the ASM Handbook (2006), prevention of corrosion can be done through various methods such as coatings, cathodic protection and surface preparation. The Canadian Energy Pipeline Association (CEPA) member companies suggests that surface preparation for new constructions of pipelines can be done, such as fusion-bonded epoxy (FBE), liquid epoxy, urethane, extruded polyethylene, and multilayer or composite coatings (Beavers & Thompson, 2006). Fusion-bonded epoxy (FBE) coatings are integrated in pipeline construction by CEPA for natural gas distribution pipeline. CEPA has a performance of 99% safety with this approach (Canadian Energy Pipeline Association, 2015).
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6 SPECIFIC FUNCTION AND FUNCTIONAL REQUIREMENTS Natural gas distribution lines serves a specific purpose of distributing refined natural gas directly to residential areas and commercial customers. The operating parameters for natural gas pipelines consists of gas composition, pressure, temperature, and ambient conditions. The type of distribution pipeline chosen is underground distribution pipelines. The functional requirements for distribution pipelines rely heavily on the operating parameters. 1. Corrosion-resistant: Depending on gas composition, distribution pipelines need to be manufactured suitable with the type of substance that passes through it. Thus, materials used in production of distribution pipelines should be corrosion-resistant to the substance it carries. If the pipeline carries toxic chemical substance, the materials should be unreactive to the substance. 2. Able to withstand operating pressure: Determining the pressure plays an important role in meeting the functional requirements. Materials that make up the distribution pipeline should be able to withstand operating pressure, making strength of the material to be a vital factor. Most distribution pipelines operates at low to intermediate pressure. 3. Able to withstand operating temperature: Temperature of the operating conditions would also determine the type of materials used in manufacture of pipeline. The material should be able to withstand extreme temperatures if needed without getting damaged, such as cracking when it is too cold. 4. Long-lasting in ambient condition: For underground pipelines, one ambient condition that should be considered is the soil humidity or acidity, to determine what material would be able to hold out against these conditions. 5. Cost-effective: Distribution pipeline network is extensive and requires a large production. Getting the right materials would also mean that cost factor has been weighed in to prevent a high expense both to the manufacturers and buyers.
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7 DESIGN CONCEPT
Figure 1: Simple design concept where 1 – internal surface, 2 – external surface
The basic design of this pipeline is mainly just choosing the type of materials. Instead of having only one type of material, the design consists of choosing two materials, each for internal and external pipe surface. The reason for this approach is due to the consideration that protective layer should be external, given the fact that processed natural gas does not have much corrosion issue to deal with. The focus should be on the outer pipe surface where the pipeline would be in contact with underground environment. As for the dimensions, the outer diameter of the pipe should be in the range of 18” in to 24” in.
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8 LIST OF SUITABLE MATERIALS 8.1 MATERIALS FOR ANALYSIS 1. Steel: Carbon steel are the most common materials used in the making of distribution pipelines due to its strength against pressure (American Petroleum Institute, 2004). 2. Copper: Copper is widely used in piping applications for its resistant towards corrosion in underground environments. 3. Polyethylene: Polyethylene pipelines varies in their ability of withstanding operating conditions. Manufacturers often offers many types of polyethylene pipelines such as superior to corrosion, resistant to chemical and abrasion, easy installation process, ability to withstand great pressure, as well as slow crack progression. It is a favored choice in most underground pipelines due to the harsh and corrosive environment. 4. Fiberglass: Fiberglass pipelines are excellent in resisting corrosion.
8.2 DISCOUNTED MATERIALS 1. Cast and wrought iron: Despite the fact that cast and wrought iron being among the oldest type of materials to be used for pipeline production, pipelines constructed of cast and wrought irons poses a high risk of safety due to the degrading nature of iron alloys. States in the US has taken initiatives to replace old pipelines made of cast and wrought iron over the years due to many pipeline burst incidents (US Department of Transportation, 2015).
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9 SUITABILITY OF MATERIALS: RANK AND INDEX OF MATERIALS There are many factors affecting the choice of materials. These factors are: 1. Corrosion-resistant: The capability of materials to withstand damage caused by oxidation or other chemical reaction should be high. 2. Maximum service temperature: The maximum temperature at which the materials can be used in the system of the pipelines. 3. Toughness of materials: Materials should have high strength and toughness for the high impact operations. 4. Cost of materials: Material selected should not be too expensive. Materials
Corrosion-resistant
Polyethylene Fibreglass Carbon steel Copper
High Medium
Table 1: Corrosion-resistant classification for considered materials
Materials
Maximum service temperature (°C)
Carbon steel
200 – 400
Polyethylene
0 – 200
Copper Fibreglass
-30 – 150
Table 2: Range of maximum service temperature for considered materials
Materials
Toughness (kJ/m2)
Polyethylene
6 – 100
Fibreglass
40 - 100
Carbon steel
2 - 80
Copper
10 - 60 Table 3: Toughness for the considered materials
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Cost (£/kg)
Polyethylene
0.5 – 0.7
Carbon steel
0.2 – 0.8
Copper
0.9 – 2.0
Fibreglass
2.0 – 10.0
Table 4: Cost for considered materials per kilogram
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10 SELECTED MATERIALS Specification of operating conditions is important in finalizing a choice of material. Refined natural gas for commercial and industrial applications has a composition of 87 – 96% methane where most contaminants such as water, impurities, and other gases such as carbon dioxide and sulphur are removed (Canadian Energy Pipeline Association, 2015). For this reason, internal pipe corrosion is considered to be negligible. Therefore, the main corrosion concern is uniform corrosion from soil humidity or acidity. Most distribution pipelines operate and a rather low pressure ranging from 30 psig to 60 psig. Temperature of natural gas exiting compressors are high (100 F – 120 F), however once the natural gas flows underground, rapid decrease in temperature occurs where the gas temperature is approximately similar to the ambient underground temperature. These conditions are the reference conditions in material selection. Based on the rank generated, polyethylene and fiberglass would be the strongest materials resisting corrosion, compared to carbon steel and copper. Since external corrosion is the main issue, polyethylene and fiberglass are the two materials to be selected from when choosing external ‘coating’ of the pipeline. Based on the material selection chart of ‘Strength vs maximum service temperature’, carbon steel can withstand up to 400 °C (equivalent to 752 F), which is extremely high compared to what was operationally required. Copper and polyethylene has a maximum service temperature of 392 F. All materials are suitable for this distribution pipeline in regard to temperature. In terms of durability, copper would not be preferable due to its brittle nature. ‘Strength vs toughness’ chart shows that polyethylene has the highest strength, secondly, carbon steel and lastly, copper. On the other hand, although fiberglass lasts well in corrosive environment, maintenance would be highly expensive. Furthermore, the inability to weld fiberglass leads to complications in bending pipes leads to the necessity to design around the piping layout to apply bends and offsets (Uberti, 1976). Copper and fiberglass is discounted from the main list for strength and weldability reasons respectively. The material narrows down to two; carbon steel and polyethylene. Adapting the design concept, the material selected for interior pipe is carbon steel, mainly because of its strength and ability to work well with operating pressure and temperature. As for the exterior pipe, or simply put, surface coatings, polyethylene is chosen to resist corrosion from the surrounding underground environment.
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11 OTHER FACTORS AFFECTING CHOICE OF MATERIALS 11.1 WELDABILITY AND JOINING Distribution pipelines go over great distance to cover a large residential area. Logically, the pipeline would not be straight from end to end. Bends are therefore needed, and different degree of pipe bends are joined and welded together to form a complete network. Thus, materials need to be weldable for this purpose.
11.2 ENVIRONMENTAL FACTOR Pipelines that is put in high toxic environments should be built upon materials that can hold against these extreme conditions. Normally, residential areas have safe land and soil contents, hence, this is not a very important factor in this case. However, it can be a very important factor given that the conditions were different. Another environmental factor is the concern on whether the materials used is safe for the environment it is in. The pipelines installed should not pose a risk to the soil, water, or air content. Harmful materials can lead to large health and ethical consequences.
11.3 AVAILABILITY OF MATERIALS Materials chosen for pipelines manufacture should be abundant. Rare materials may lead to a slow-paced production because of supply shortage.
11.4 MAINTENANCE Materials that deteriorate easily means maintenance would be more frequent. This can be costly and for underground pipes, it would require a lot of repetitive diggings when replacements are needed. In some cases, more expensive materials could be favored in order to cut future maintenance cost over time.
11.5 MISCELLANEOUS SHOCK FACTORS Underground pipes experience a lot of sudden pressure and vibrations such as heavy traffic on roadways or construction work on nearby lands where pipelines are installed. Because of this, materials should be resistant to shock.
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12 POSSIBLE IMPROVEMENT There are several possible improvements that will allow the distribution line to work at its optimum efficiency. 1. Internally coated – Coating the pipeline internally should be considered as it would help to reduce the friction in the pipeline. 2. Consideration of materials’ grades – Different grades of same materials performs according to their grades. For example for polyethylene, PE 100 have higher strength and toughness than PE 80. Thus, PE 100 can operate at higher operating pressures than PE80 pipes for the same wall thickness. 3. Accuracy in calculation – The measurement of compression and pressure from inside and outside of the pipe must be accurate because it will lead to the selection of materials and size of pipeline that can operate optimally based on the value calculated.
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13 CONCLUSION AND RECOMMENDATIONS Distribution pipeline is one of the many types of transportations to deliver oil and gas such as crude oil and natural gas. This report explores the material selections for natural gas distribution pipeline where natural gas will directly transport to residential areas and commercial customers through distribution pipelines. The main focus is selecting materials that meets the functional requirements, while significantly looking into the matter of internal and external corrosion. For this design, the main concern was only for external corrosion. Five main operating parameters were listed in the process of choosing the materials for distribution pipeline. It must be corrosion-resistant to substance it carries, being able to withstand operating pressure as well as operating temperature, long-lasting in ambient condition and made of cost-effective materials. Distribution pipeline is separated into two parts, internal and external surface. Therefore, materials selected for both surfaces were different considering the condition of the surfaces be in contact with. Comparing both surfaces, external surface is more prone to heavier corrosion issue as the layer is widely expose to underground environment where variety factors of corrosion have to be considered. The range of outer diameter pipe is between 18’’ to 24’’. The suitability of materials was ranked in order of materials fitting the needs of the pipeline. In order to finalize the choice, the materials were narrowed down based on material selection chart. As a result, carbon steel was selected as the type of interior pipe and polyethylene as the type of exterior pipe. It is recommended that other factors are to be considered in choosing materials for pipelines such as weldability and joining of pipeline, environmental factor, availability of materials, maintenance and miscellaneous shock factors. Throughout the research, the main source for measuring pipeline performance based on materials was Canadian Pipeline Energy Association. To further obtain a guarantee on whether the materials selected are in fact best suited to the process, a more in-depth research should be done. More reports by companies using these materials for the similar purpose should be reviewed to increase the possibility of selectin the best materials.
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14 REFERENCES American Petroleum Institute, 2004. Specification for Line Pipe. [Online] Available at: https://law.resource.org/pub/us/cfr/ibr/002/api.5l.2004.pdf [Accessed 8 Sept 2015]. American Society of Metals International, 2002. Corrosion. In: ASM Handbook Volume 11, Failure Analysis and Prevention . Materials Park: ASM International, pp. 761 - 795. Beavers, J. A. & Thompson, N. G., 2006. External Corrosion of Oil and Natural Gas Pipelines. In: ASM Handbook, Volume 13C, Corrosion: Environments and Industries. Materials Park: ASM International, pp. 1-12. Canadian Energy Pipeline Association, 2015. Maintaining Safe Pipelines. [Online] Available at: http://www.cepa.com/about-pipelines/maintaining-safe-pipelines [Accessed 11 Sept 2015]. Canadian Energy Pipeline Association, 2015. Natural Gas Pipelines. [Online] Available at: http://www.cepa.com/about-pipelines/types-of-pipelines/natural-gas-pipelines [Accessed 5 Sept 2015]. Uberti, G. A., 1976. Fiberglass Reinforced Piping for Shipboard Systems, Falls Church: National Steel and Shipbuilding Company. US Department of Transportation, 2015. Pipeline Replacement Updates. [Online] Available at: http://opsweb.phmsa.dot.gov/pipeline_replacement/ [Accessed 13 Sept 2015].
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15 APPENDIX Attached are: 1. Peer Review 2. Material selection charts used in this report
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15.1 PEER REVIEW The report touches in detail on what each material is resistant to. This gives a further understanding on which material works best in certain environment. Upon ranking of materials, reasons are discussed thoroughly on why the materials are ranked first, second and so on. It stays within the context of fulfilling the design concept and meeting operational requirements. This clarifies the process of selection material even further. Calculations also assisted in understanding the reason behind final selection. However, the specific design was unclear until about a few pages in. It was not stated clearly anywhere that the heat exchanger designed was a water heater, seemingly a water heater for shower. The conditions associated with the requirements for the application was not mentioned. The report also did not cover on other factors affecting choice of materials. There were no articles or research paper on the literature review. Use of language is sometimes spoken-language, such as “…two different types of material like copper and aluminum will certainly cause different reaction since their property is totally different.” in the introduction section, and “To get the right material, the first thing is to consider the purpose of this machine, like to build a car for normal people..” in the conclusion section. Overall, report covers great depth behind material selection process. For future improvements, what the design is should be stated clearly in the introduction. Language use should also be report-appropriate.
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15.2 MATERIAL SELECTION CHARTS
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