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MEC3203 Materials Technology

Published : 18-Sep,2021  |  Views : 10

Question:

Provide an analysis of the potential causes of failure based on an extensive review of literature Review and critique the initial "failure report" as prepared by the ATSB; comment specifically on whether the methodology is suitable and adequate based on your extensive review of literature Comment on whether additional information or additional investigation is required (eg sample testing);  Recommend suitable solutions or rectification to the problem (based on certain assumptions).
 
Provide an outline and analysis of the performance requirements  Evaluate and select an appropriate materials selection method. 15 3) Systematically justify your selection of materials for the equipment.

Answer:

The failure of blowout preventer (BOP) of BP Deepwater Horizon happened on April 20, 2010, making it the worst oil spill disaster in the U.S. history. On that fatal day, there was rapid and unusual expansion of methane gas from the well through the drilling riser which then found its way into the drilling rig. The methane gas accumulated in the drilling rig and generated excess heat and pressure that collectively ignited the gas. There was the first explosion that sent the crew into panic. They tried to close the well using the BOP but the device failed. As a result, the whole rig caught fire leading to a big explosion. The platform sunk completely after two days. Failure of the BOP to seal the well resulted to vast volumes of oil spilling into the Gulf of Mexico. This continued for several days. Figure 1 below shows a photo of the Deepwater Horizon oil rig on fire.

Investigations conducted into this disaster found that failure of the BOP was instigated by buckling of drill pipe. BOP is a safety device or valve that is used to close the well during an emergency thus preventing flow of gas, oil or mud above the sea floor. This device is usually fixed on top of the wellhead at the sea floor. Another component of the oil rig known as drill pipe is a hollow tube that is used for transmitting drilling torque. It also facilitates movement of gas or oil being drilled flows from deep in the well into the rig on surface. The drill pipe passes through the BOP at the sea floor, as shown in Figure 2 below. The BOP and drill pipe are connected in such a way that during an emergency, the former cuts the latter thus stopping flow of oil or gas from the well, which could otherwise lead to a possible explosion through a process known as gas kicking (Hammer, 2010).

BOP consists of several components, including annular preventer, pipe ram, blind shear ram and blind ram, as shown in Figure 3 below. Blind shear ram is a hydraulic device that has 2 cutting blades. During an emergency, the blind shear ram shears or cuts the drill pipe thus sealing the well (Aresco LP, 2017; Gold, 2014). The pipe ram gets activated a forms a seal or cover between the exterior of the drill string and the well bore. The function of the shear ram is to cover the well bore if the well does not have the drill string. Lastly, annular preventer is used for sealing any object found in the well bore. In this disaster, the BOP failed to perform its intended function because it did not cut the drill pipe and therefore methane gas continued flowing and accumulating in the rig (U.S. Chemical Safety Board, 2014). As stated before, the failure of BOP to perform its function was due to buckling of the drill pipe. The buckling occurred due to effective compression mechanism. The mechanism happens due to pressure gradient between the interior and exterior of the drill pipe. In this case, the pressure inside the drill pipe was very high compared to that outside the drill pipe. Besides that, investigations found that the wiring of BOP was faulty and its battery was dead, which also contributed to the device’s ultimate failure (Mullins, 2010). Therefore the ultimate malfunctioning of the Deepwater Horizon BOP was as a result of a series of human errors.

The owner of Deepwater Horizon oil rig was BP, a British company, while the operator was Transocean, a Swiss firm. The oil rig was built by a South Korean company, Hyundai Heavy Industries. By the time of the spill, Deepwater Horizon oil rig had been in operation for almost a decade. The rig was drilling in the oil field of Macondo Prospect, in Gulf of Mexico, which is about 50 miles on the southeastern side of Louisiana coast. The oil rig was operating on an exploration well.

Some days before occurrence of the disaster, the rig had exhibited some unusual pressure upsurge. About 7 hours before the explosion, BP and Transocean executives had conducted a joint supervision visibility tour to share particular safety information with the crew and celebrate the milestone they had achieved – completing the exploration successfully and capping the well waiting for a production unit to be brought so as to commence harvesting of gas and oil from the oil field (Hoffman, 2010).  During this tour, there were numerous discussions on how to conduct negative pressure testing in addition to approaches of interpreting results from pressure tests. Some executives recognized that there was confusion and misunderstanding among drillers.

Most of the pressure tests were misinterpreted (Mullins, 2010). On that same day, work started to replace the drilling mud with seawater. During this process, some oil started flowing into the well’s bottom. If the crew had correctly interpreted the results of negative pressure tests, they would have realized that there was already an internal oil leakage inside the well. As workers continued removing mud from the well and replacing it with seawater, which was of lesser volume, oil continued accumulating at the bottom of the well. The workers were setting in place the well’s cement cap, easing tension that was being applied on the drilling risers. This was done with an aim of sealing the well temporarily (Pallardy, 2017). However, the continued increase of pressure led to closure of seawater and mud pumps, but things did not get any better. At this time, the crew were not able to monitor the fluid and pressure imbalance in the well. The fact is that the crew was removing one remaining barriers against gas kicking without closely monitoring the outcome (NASA Safety Center, 2015).  

Before this disaster, both BP and Transocean had been accused of making some unethical decisions in their drilling activities. BP was known for their cost-saving and quick options without considering possible negative impacts (Brooder, 2011a; Brooder, 2011b). In 2005, their oil refinery facility in Texas City exploded but the way they handled the situation was not convincing (McMasters, 2015). Just 4 months before this disaster, Transocean had experienced a blowout in North Sea, which resulted from their crew assuming the safety of the well and failing to monitor its performance (NASA Safety Center, 2015). Therefore it seems that their safety management and emergency response plans were not effective.  

According to Associated Press (2014), the BOP that was used in Deepwater Horizon oil rig had not been tested despite its manufacturer, Cameron International, having recommended for a safety test before installation. The manufacturer was probably not 100% sure of the safety of the BOP and that is why he recommended the operator and owner of the oil rig to test it before putting in into operation. It was also wrong for Cameron International to sell a BOP that had some safety questions but it is likely that BP insisted to purchase the device because it did not want any further delays to its drilling schedule. Besides that, it is always recommended for oil rig owners and operators to regularly collect real-time data demonstrating the behavior and performance of various components of the oil rig. Some of the most important components to in this data recording exercise are safety devices such as BOP. Collection of real-time data helps in exploring the performance of the component and identifying any defects or unusual behaviors before they get out of hand.  

1.2. Background on Operating Environment

Deepwater Horizon was an ultra-deep water drilling unit on an oil field of Macondo Prospect. The platform was approximately 121 m long and 78 m wide. It was designed to operate in waters to a depth of 2.4 km and its maximum drill length was about 9.1 km. The platform was alleged to have been used in drilling at very deep waters of up to about 10.7 km. BP purchased the minerals right to start drilling oil on Macondo Prospect in 2008. The platform started drilling the oil in 2010 at a depth of about 1.5 km. When the disaster occurred, drilling was being done on an exploratory well. According to the plan, the well had was to be drilled to a depth of 5.6 km below sea level, after which it would be sealed and adjourned to be completed later as a undersea oil producer. The process of sealing the well was almost complete and what was being done was to run the production casing and cementing. After cementing, the next process was to perform the integrity test of the well and set a cement plug so as to abandon the well temporarily with assurance that it was safe.

At the time of the accident, the platform had a total of 126 people onboard. Out of this number, 7 were BP employees, 79 were Transocean employees and the remaining 40 were staffs from different firms. The explosion killed 11 workers. The oil spill lasted for 87 days from, April 20, 2010 to July 15, 2015 when the well was temporarily sealed. During this period, it was estimated that there was an oil leakage of approximately 780,000 m3 into the Gulf of Mexico (Adams and Gabbatt, 2011).   

Before occurrence of Deepwater Horizon oil spill. BP and Transocean had operated for several years without major disasters. This had made the two companies to be overconfident in their operations. Because of this, majority of their drilling proposals were approved quickly and without detailed scrutiny by different federal authorities and officials. This enabled them to continue drilling very deep below the sea floor. Obviously, pressure increases with depth. This means that as the drilling depth increased, the pressure acting on the drilling devices also increased. This required improvement on the material properties of conventional drilling devices because they were exposed to very high and unusual pressure. Unfortunately, these companies did not have any extensive and more reliable safety management systems nor emergency response plans. Therefore the risk in the operating environment of Deepwater Horizon were generally higher.    

Generally, safety of oil rigs cannot be 100% guaranteed. However, there are several mechanisms that are put in place to improve safety of drilling activities. One of these is inclusion of a BOP in the oil rig. This is a safety device and is used as the last option of controlling an oil rig that has the potential of blowing out. The operation of a BOP can be manual or automatic. A manual BOP is the one that the workers must activate or operate by hand when there is danger of a blowout. An automatic BOP is the one that can detect unusual or extreme pressure differences and oil flow in the well and get self0-actiated to prevent a blowout. The BOP used in Deepwater Horizon was manually operated and the workers tried to operate it but it failed. When there is a possibility of a blowout, a BOP is used to stop flow of oil and other substances from the well into the rig through the drill pipe.

The Deepwater Horizon BOP had been in use for about 9 years. The device weighed around 400 tons and its height was approximately 17.4 m (Associated Press, 2014). This was a big device that had to be designed, manufactured, installed, operated and maintained by putting in place all appropriate safety measures. Nevertheless, BP did not always prioritize safety of such components and instead went for quick and cost-effective alternatives (Zolkos and Bradford, 2011). One of such alternatives was to take the BOP to China for modification instead of taking it to the U.S. The company chose China because it would save a significant amount of money (Web, 2010). During that time, China did not have specialized company with adequate capacity and experience to handle this kind of BOPs. At the time of purchase, BP was also advised by Cameron International to perform safety tests on the BOP but this was ignored. At some point, the crew performed crucial tests when they were investigating the integrity of the well. In the first test, they obtained very baffling results. On performing the second test, after changing the drill pipe, they obtained results that were not worrisome. As a result of this, they ignored results from the first test and made their conclusion based on results obtained from the second test that the integrity of the well way okay. This was definitely an incorrect conclusion.  

The general working environment of Deepwater Horizon was that the platform was operating at a very great depth below the sea floor. This means that the pressure acting on the drilling components was also very high. Most of these components were made of steel. The drill pipe, which contributed to the failure of BOP to seal the well, was also made of steel. Components made of steel are susceptible to a variety of failure mechanisms if they are subjected to excess loads or forces. In the case for Deepwater Horizon, the steel drill pipe was exposed to extreme pressure differences that resulted to buckling. Despite operating at very high depths, BP and Transocean did not take its real-time data collection system seriously by analyzing it as a way of ensuring close monitoring of the behavior and performance of drilling components. If this data had been collected, the workers would definitely have noticed the start of buckling of steel and taken appropriate measures of replacing it before the situation got worse. Figure 4 below is a photo of the damaged Deepwater Horizon BOP.

Analysis of the failure modes and potential causes of failure based on an extensive review of literature

When a material, system or part of it fails, there are various possible causes. It is very important to explore these possible causes so as to develop strategies that will avert occurrence of prospect related failures. This process of analysis possible causes of failure is referred to as failure analysis. In engineering, it is nearly impossible to design, manufacture and use a material, system or component that is 100% free from defects. This makes failure analysis an important process in engineering because it helps in establishing appropriate approaches of improving design and manufacturing processes, and also properties of materials. In this context, failure analysis involves probing and gathering evidence on the anomalies that are likely to have promoted the material or system failure. The process is usually comprehensive and should encompass all fine points.

For example, if a component is identified to have defects when in use, the person conducting failure analysis must examine all the processes and stages through which the product has gone through. This entails scrutinizing all possible reasons behind the failure at different stages. Some of the issues that can be examined in such a scenario include the following: possible design errors, materials selection method and quality of raw materials used, manufacturing processes used, standards applied in the design and manufacturing processes, supervision of workmanship, and whether the personnel involved at different levels of these processes, from design to maintenance, had the required qualifications to perform those responsibilities. This identification of possible reasons for material or system failure is what is called root cause analysis. Therefore failure analysis process ends when all possible root causes of the failure have been identified and scrutinized.

The main purpose of conducting root cause analysis is to establish the original or real reasons for failure and analyzing them so as to develop solutions that will prevent this kind of failures from occurring in the future (Andersen & Fagerhaug, 2009; ThinkReliability, 2017). For this to be achieved, there are several guidelines that must be followed when conducting root causes analysis. First and foremost, the main target of the process should be to identify various factors that are likely to have led to the problem. Second, the process should identify appropriate changes that should be made so as to prevent similar problems from occurring again. Several changes have to be identified and those selected should be the ones with the lowest costs of implementation. Third, crucial lessons learnt from the failure must be documented and used to prevent similar problems in the future. Last but not least, the process should be done in a systematic manner and it must be as effective as possible.

Conducting root cause analysis systematically is attained by following particular steps. The first step is to define the problem. For instance, in Deepwater Horizon, problem definition could include failure of BOP leading to explosion of the platform and spilling of the oil into the Gulf of Mexico. The second step is to gather adequate data and evidence on what really happened before, during and after the problem. This will lead to collection of very useful information about factors that are likely to have contributed to the problem. The third step is to ask for reasons and questions as to why, when and how the failure occurred. This basically involves determining the root causes of the problem. The fourth step is to establish suitable correction actions and solutions to the problem.

This involves identify a variety of possible solutions, scrutinizing each of these solutions and selecting the ones that are most suitable – those that will resolve the problem and prevent its reoccurrence. The fifth step is to implement the selected solutions. The sixth step is to make observations on the impact that the implemented solution has on the system. Here, performance of the material or system is monitored after adopting the solution so as to see if there is some improvement or not. The last step is to identify any challenges that may be caused by the implemented solutions and addressing them accordingly. The solution being probably a new one, chances of it posing some challenges cannot be ignored. Thus persons involved should look out for these challenges and develop strategies of dealing with them (Lennox Hill Ltd, 2017). If the solutions identified are not acceptable or if they are not effective in correcting the problems then the entire process has to be repeated. The chart in Figure 5 below shows systematic steps of root cause analysis (Tomic & Brkic, 2011).

When conducting root cause analysis, it is also important to know different classes of root causes. According to Mind Tools (2017), there are 3 main kinds of root causes: physical causes, human causes and organizational causes. Physical causes are those related to the type and quality of materials used, and working or operating environment and conditions. Human causes are those related to mistakes made by different people or failure to do what was required. In most cases, human causes are the ones that led to physical causes. They may include design errors, inappropriate selection of materials, etc. Organizational causes are the ones related to policies that are used to govern the activities being undertaken. This may include improper maintenance of a system, making risky assumptions, not following recommendations by the materials manufacturer or supplier, and performing activities without following appropriate standards, etc. Another very important element in root cause analysis is to ensure that the team conducting this process has the right knowledge, skills and experience to scrutinize the problem comprehensively and establish effective resolutions (Lee et al., 2008).   

Before starting the process of root cause analysis, it is also very important to select appropriate tools and techniques to use. Some of these may include: causal factor tree analysis, fault tree analysis, change analysis, barrier analysis, current reality tree (CRT), Pareto analysis, Bayesian inference, five whys analysis, and failure mode and effects analysis (FMEA), among others (Bowen, 2011).

There are also different methods of collecting evidence or root causes. Some of these include: physical observations (where the team goes to the site where the problem has occurred and inspects various materials physically), witness interviewing (where the team interrogates persons who witnessed how the problem occurred, including workers, passersby or neighboring residents) and video footage (where the team collects information by watching events as caught on camera). Information gathered using these methods is usually enough to help the team establish the likely causal factors to the problem. When gathering evidence, it is also important to ensure that any objects or materials collected from the site of the disaster are properly transported and stored for accurate analysis. During the analysis, various tests have to be performed on the material that failed and the results obtained compared with standard results. Some of these tests include: mechanical testing, chemical analysis, no-destructive testing, etc. If these tests do not provide adequate information about the performance of the material, non-destructive testing may be conducted.

In engineering, a failure mode refers to a mechanism that leads to a material failing to perform as anticipated. In other words, it is a process, way or manner in which a material’s functionality fails. There are different types of material failure including, but not limited to: corrosion, wear & tear, excessive deflection, thermal shock creeping, ductile fracture, brittle fracture, buckling, fatigue, yielding, etc. These failures can be caused by design defects, manufacturing imperfections, operational anomalies, or maintenance flaws. Design defects or deficiencies are problems that arise from design stage of a component. This may be due to improper design, design errors or omissions, miscalculations, wrong choice of materials, non-compliance with industry standards, etc. If a design defect is not corrected during the design stage, there are high chances that the final product will be defective. Manufacturing imperfections are problems caused by use of incorrect manufacturing technique or procedure when creating the product. Operational anomalies arise when the material is installed or used inappropriately or in conditions it was not designed for. For instance, applying excess load than design load on a material is an operational anomaly.

Operational anomalies may arise be caused by inadequate supervision and monitoring of activities, poor workmanship, failure to meet the required operation standards in the industry, and non-compliance with manufacturer’s recommendations. Maintenance defects are those that arise when the material is not properly maintained. If this happens then it is very difficult to identify any defects and correct them before they cause problems. Therefore when conducting failure analysis, it is important to consider the specific type of design approach that was used when the material was being designed, the manufacturing procedures that were utilized, environment or conditions under which the material has been operating, and maintenance activities that have been performed on the material.  

Suitability of a material for particular engineering applications is mainly determined by its physical, mechanical and chemical properties. For this reason, it is very important to critically analyze properties of a material so as to establish whether it is suitable for the intended use or not. Various investigations carried out on Deepwater Horizon oil spill found that the main cause of the accident was failure of the BOP. This was instigated by buckling of drill pipe, which resulted to misalignment of blind shear rams, as shown in Figure 6 below. Because of this, the blind shear rams could not cut off the drill pipe to stop gas kicking.  

Buckling is one of the most common types of failure modes in metallic materials. Since the drill pipe was made of steel, it was susceptible to this failure and several others. As stated by Akin (2010), a material buckles when it loses stability as a result of excess load being applied on it. This failure mode is very risky because its occurrence comes even before the material attains its yielding point (Cyprien, 2017). Buckling is caused by a factor referred to as slenderness ratio. This failure is very common in columns because of their slenderness ratio (the relation between the column’s length or height and its width) (Quimby, 2011). In the case of Deepwater Horizon, the slenderness ratio was the relation between the height of the drill pipe and its diameter. The slenderness ratio was very big because the drill pipe was relatively long compared with its diameter. In other words, lateral dimensions of the drill pipe were weak hence the probability of buckling occurrence on it was very high.  

There are several causal factors for the buckling of steel drill pipe of Deepwater Horizon. These include design defects, manufacturing imperfections, operational anomalies and maintenance flaws. Design defects are possible causal factors because the design team of the drill pipe failed to painstakingly assess the performance of steel when it is exposed to large pressure difference. It was important for the design team to use computer simulations so as to understand the relationship between pressure and performance of the drill pipe. As a result of this, the design team would probably have recommended alternative materials that are more resistant to buckling. The drill pipes had large slenderness ratio hence the possibility of buckling could not be ignored. Since steel is at high risk of buckling, the design team would have identified the need of using alternative materials because the working conditions or environment were characterized by very high and unpredictable pressure differences which increased buckling possibilities. Therefore wrong choice of material was the major deficiency during the design process.

Manufacturing imperfection was another possible cause of failure of the BOP used on Deepwater Horizon. At the time of purchase of the BOP, Cameron Internal, the device manufacturer, insisted that BP and Transocean must perform safety tests before installing and using the device. This is likely to mean that the manufacturer had used inappropriate processes to fabricate the device and therefore was not sure of its safety. There is also a possibility that the purchasers wanted the device quickly and therefore the manufacturer had to sell it before performing all required industry standards. As a specialist in the manufacturer of BOPs and other drilling devices, Cameron Internal was fully aware of the potential risks of selling the device before completing all the required standards. To abide by the industry code of ethics, the manufacturer should have insisted on performing all the required tests so as to be sure of the device’s integrity before selling it. Therefore it was unethical for the manufacturer to sell the device without having knowledge about its integrity. Besides all these, it was also found that wiring of the BOP was faulty. This is another major manufacturing defect because it means that the manufacturing process applied did not follow allow the design specifications. Otherwise, a problem such as default wiring could not have occurred.

The third possible cause of failure in Deepwater Horizon was operational anomalies. There were several irregularities that are likely to have caused the failure. One of these was the incorrect cementing process. Before occurrence of the explosion, exploration on Macondo Prospect had been completed and the well had to be sealed temporarily, awaiting start of actual production activities. Cementing had to be done so as to seal the well and prevent any possibility of the gas or oil flowing from the well’s productive reservoir (Brooder, 2011b). The cementing services were provided by Halliburton. Unfortunately, the cementing was done improperly and this resulted to oil and gas leakage. This leakage led to rapid increase of pressure in the wellbore that caused the drill pipe to buckle.

Another operational anomaly was misinterpretation of the pressure tests performed by the crew after cementing the well. The tests performed were two and each presented different results. The results from the first test were very worrying as they indicated that the well pressure was abnormal hence the integrity and safety of the entire facility was uncertain. The crew decided to change the drill pipe and conducted the second test. The results obtained from this test indicated that the pressure inside the wall was normal and therefore no call for alarm. The crew decided to ignore the first results and decided to assume that everything was okay.

This was an anomaly because the results from the first test should have prompted the crew to start analyzing possible factors that may have resulted to the abnormal temperatures. Besides all these, it was later found that the crew had misinterpreted the pressure test results. According to the crew’s interpretation, the well pressure was within normal ranges but this was not the case. As stated before, the cementing process was inappropriately done and pressure was continuing to accumulate inside the wellbore. However, the crew misinterpreted the pressure test results and continued with normal operations. The misinterpretation was because of lack of qualified persons among the crew members. A few hours later, pressure exceeded normal ranges, caused the drill pipe to buckle and the well could not be controlled after the BOP failed to seal it.

Lack of close supervision and monitoring of the real-time data collection system was another operational anomaly that caused the failure. Considering the risky conditions under which an oil rig operates, it is only sensible to ensure that the platform has an integrated system for collecting real-time data and transmitting it to an offshore system so as to help the crew in ensuring continuous monitoring and supervision of drilling activities. If real-time data is collected and used, and the activities are properly supervised then it becomes very easy for the crew to notice if there are any abnormal pressures in the well. Deepwater Horizon did not use the real-time data collection system appropriately and therefore the crew could not detect if there were abnormal pressure values. As a result of this, pressure continued to increase to very high levels without being noticed, which then caused the drill pipe to buckle. There were also no supervision records showing how the team periodically monitored and controlled the operations.

Lack of proper qualification and negligence of workers were other operational anomalies that caused failure of the drill pipe. This was exhibited in several incidences including improper cementing, misinterpretation of results and incapacity to identify any abnormalities at an early stage. It basically means that the crew did not have the capacity to detect hazards and risks, examine them quickly and establish proper approaches of mitigating them.

The last operational abnormality that is likely to have contributed to failure of Deepwater Horizon was lack of an emergency response plan and team. Drilling operations are generally risky and therefore one of the strategies of enhancing safety is developing an emergency response plan. The purpose of the plan should be to try and control the impacts of a well that is out of control. If there was a plan then a large percentage of volume of oil that spilled in the Gulf of Mexico would have been directed to a designated facility thus reducing the negative environmental impacts that were caused by the blowout. Besides that, this team would have responded quickly and possibly replaced the drill pipe immediately the pressures were detected to be more than anticipated or when the drill pipe showed any signs of buckling.              

The fourth and last possible cause of failure of the BOP of Deepwater Horizon was maintenance flaws. The companies involved in drilling operations of Deepwater Horizon made several maintenance mistakes. One of this was the decision made by BP to rectify the BOP in China instead of doing so in the U.S. The company decided so because they wanted to save money and time. They disregarded the safety and structural integrity implications of this decision even though they knew that during that time, China did not have specialized companies to rectify the BOP appropriately. As a result, the company selected did not scrutinize the ability of the steel drill pipe to operate appropriately deep undersea. At the end, the drill pipe failed because it was exposed to very high pressures that it could not sustain.

Another maintenance flaw was demonstrated by failure of the BOP and gas alarm system. A few minutes before the explosion, the crew tried to close valves in the BOP but they all failed. This simply meant that the BOP had not been maintained properly or else the valves would have been rectified and ensured to be in proper working condition. In addition, it was found that the BOP’s battery was dead and therefore the device could not automatically activate its safety mechanism. The wiring of the BOP was also defective thus the entire device could not work. Last but not least, the gas alarm system of the platform failed and therefore the crew was not able to close ventilation fans on time and stop the gas from causing an ignition. All these failures were as a result of improper maintenance of the BOP and the entire system.

In one way or the other, all these possible causes of failure resulted to the abnormal pressure upsurge in the wellbore. This caused the steel drill pipe to buckle and failure of the BOP to seal the well and prevent a blowout.  

Review and criticism of the “failure report” as prepared by the experts; commending on the whether the methodology is suitable and adequate based on your extensive review of literature

The report title “Deepwater Horizon Accident Investigation Report” was released by BP on September 8, 2010, about 4 months after occurrence of Deepwater Horizon explosion. The report was prepared by an internal BP investigation team and all views contained in it are solely those expressed by the team. The team focused on exploring events that led to the accident, key findings that are related to the various events that resulted to the accident, and recommendations that can be used to prevent similar accidents. The team worked independently and did not benchmark its investigation processes or findings with those of other companies, individuals or investigation teams. The team collected information and data from a variety of sources. This included physical observations, even though they did not access the platform by the time they were conducting the investigation, interviewing witnesses, real-time data and public hearings testimonies. The team engaged more than 50 internal & external experts from different fields to help them complete the investigation.

The report consists of 7 sections. Section 1 is scope of the investigation; section 2 is the Macondo well; section 3 is chronology of the accident; section 4 is overview of the accident analyses; section 5 is the accident analyses; section 6 is recommendations of the investigation; and section 7 is work that the team did not conduct. Section 1 highlights the scope of the investigation, investigation process used and how the investigation team shared their insights. Section 2 has documented various elements of Macondo well including: lease & permits, well design & planning, and summary of drilling operations. In section 3, major activities that happened before, during and shortly after Deepwater Horizon explosion have been discussed.

This includes a series of events before April 19, 2010, final casing run, cementing work, positive & negative pressure tests, well monitoring & concurrent operations, well control response, oil rig explosion & fire, and emergency operations of the BOP (BP, 2010). Section 4 discusses an overview of detailed analyses that the investigation team undertook. The 8 key findings identified have also been discussed. Section 5 discusses further the analyses of the accident and recommendation for each critical factor analyzed. Section 6 highlighted various recommendations based on the 8 key findings identified. The recommendations are categorized as: engineering technical procedures and practices, competency and capacity, audit & verification, management of process safety performance, and assurance and oversight of service providers and contractors. Section 7 highlighted what the investigation team did not do, including failure to test the cement used, failure to have physical access to the Deepwater Horizon BOP, and failure to get a representative BOP system from Cameron International.

The information contained in this report is very useful in preventing similar accidents from occurring. The investigation team used investigation analysis process of BP together with chronology and fault tree analysis. Therefore the methodology used in conducting the investigation was suitable and adequate. This is because it adequately identified critical factors that caused the accident, which were used to come up with recommendations for preventing occurrence of similar accidents. However, the investigation team should have completed the work they did not done (which is contained in section 7) because this was the most important work. The various tests that the team did not complete are the ones that would have given a real picture of how material properties of various components and processes contributed to the BOP failure, and the accident as a hole. The undone work would also have helped the investigation team to know whether Cameron International made any design or manufacturing mistakes when fabricating the Deepwater Horizon BOP that failed. Therefore the methodology used in this report was right but it was not implemented fully.

Commending on whether additional information or additional investigation is required (e.g. sample testing or validation required)

The need for additional investigation and information in this report is certain. By the time the team was carrying out the investigation, all objects from Deepwater Horizon had not been recovered and the team could also not have physical access to the platform and they were unable to perform a wide range of crucial tests and examination. There was need to examine and test the BOP stack, establish material properties and configuration of the drill pipes, examine the configuration of hydraulic control system of the BOP, determine the 2 check valves’ conditions, and test Bop batteries for automatic mode function. There was also need for further investigation and tests on the cement that was used for seal the bottom of the well.

These included testing the nitrified cement slurry, determine whether the method used to produce the cement was appropriate, test fluid rheology, test cement slurries of base & foam, test the properties of cement additives that were used and their suitability, perform settlement tests, test fluid loss in base and foam slurry, and test the contamination effects that the spacer, base oil and mud had on cement slurry. Last but not least, there was need to get a representative BOP from Cameron International and perform a series of tests including: determining annular preventers’ response time under the pressure conditions in the wellbore, determine erosion properties of the annual preventer and BOP valves, and examine the blind shear rams of the BOP. These tests would provide detailed and crucial information about material properties that contributed to failure of Deepwater Horizon BOP.

Recommend suitable solutions or rectification to the problem (based on certain assumptions)

First and foremost, Cameron International must review its design and manufacturing processes. The design team should comprehensively analyze properties of materials used to manufacture various drilling components. The company should also ensure that it uses appropriate manufacturing processes so that the components it produces meet the required industry standards. It must have a quality assurance system to ensure that every component sold meet the minimum industry standards. Halliburton should also review the additives used in making the cement slurries, the mix design and cementing procedure it applies. BP and Transocean must ensure that they employ qualified staffs to operate the oil rig, including performing necessary tests. This will ensure that the staffs are able to detect early signs of abnormalities and take quick actions. They will also conduct necessary tests accurately and interpret results correctly. The two companies must also closely monitor all ongoing activities on the platform. This can be done by making use of real-time data collection system. The offshore staffs should be keen on analyzing the graphs plotted by this data so as to detect any abnormalities. All supervision and management records must also be kept in a professional manner.  

BP and Transocean must have a systematic maintenance system to check the working conditions and performance of all components periodically. This will help in detecting any mechanical problems at an early stage and rectify them before they can cause any major problem. Maintenance activities must also be done by reputable companies. Also, the companies must follow manufacturers’ manuals and recommendations when using any component purchased externally. Additionally, the oil rig operators must have a comprehensive crisis management plan. This includes a reserved or nearby infrastructure or facilities that can contain or absorb possible leaks. If Deepwater Horizon had an absorbent perimeter wall built around it then most of the leaked oil would have been absorbed. This would help in containing the oil within the isolated area only. It is also important for drilling companies to invest adequate resources in creating a highly-trained and well-equipped response team that is always on standby for any emergency.

The companies should also ensure that they employ qualified personnel only. Last but not least, all companies must always examine possible implications of all decisions they make. They should find a way of balancing between safety and time and money saving.

An outline and analysis of the performance requirements

The process of selecting materials for any engineering application is very important and must be done with utmost thoughtfulness. According to Ehinger et al. (2015), materials selected have great and direct impacts on the performance of the final product created. In most cases, this process aims at minimizing cost and environmental impacts of the product, and ensuring that the product meets the performance goals (Maggs, 2012). The case study discussed in this report points to failure of the drill pipe as one of the major factors that contributed to the accident. Drilling pipes play a key role in oil rig activities because they assist in pumping the drilling fluid down the hole.  The drill pipe in Deepwater Horizon failed because it was made from steel, which is a material that is vulnerable to buckling. It is worth noting that the working conditions of drill pipes are characterized by high and fluctuating pressure, which expose these components to risks of fatigue, wear and tear (Spoerker, Havlik and Jellison, 2009). The extremely high pressure caused the steel drill pipe to buckle thus making it difficult for the BOP to operate as intended.

From the failure of the steel drill pipe, it is necessary to find alternative materials that can be used instead of steel. The materials have to be selected by considering certain performance requirements, which include: mechanical, physical, chemical and manufacturing properties. The specific performance requirements of the materials are: high stiffness, high impact strength, high fatigue resistance, lightweight, superior thermal resistance, ductility, excellent vibrational resistance, corrosion & erosion resistance, machinability, and durability (Jayakody, 2011; Trivedi, 2014). Besides that, it is also important to consider environmental and economic factors of the material. In general, the selection process should ensure that the material selected provides optimal performance within anticipated operating environment.

Evaluation and selection of an appropriate materials selection method

There are different methods of materials selection. Some of these include: cost vs. performance, failure analysis, weighted property method, cost-benefit analysis, value analysis, etc. Cost vs. performance method entails analyzing materials based on their total costs (manufacturing, operating and maintenance costs) in comparison with their performance. Weighted property method involves assigning weights or indices on every material requirement depending on its relevance. The method is starts by quantifying or establishing a weighting factor (α) based on how important the requirement is. The next step is to determine the suitability of each material to satisfy the performance requirements and assign a scaling factor (β). After that the performance index is determined by multiplying the two factors, i.e. α x β. Cost-benefit analysis is a method used to select materials by considering the ability of the material to save more money.

Value analysis method entails selecting materials by considering the value that each material adds to the performance of the final product. Considering these materials selection methods, the most suitable method is weighted property method. This is the best method when selecting alternative materials. The method will compare alternative materials that can be used to make drill pipes instead of steel. Potential materials can be: polymers, glass, wood/timber, rubbers, other metals, metal alloys, foams, plastics, elastomers or composites. But considering the performance requirements discussed in the previous sections, some of these materials can be eliminated through initial screening because they do not meet crucial performance requirements. The screening can be done using Ashby’s method.

Systematic justification of the selected materials for the equipment

The steel drill pipe of Deepwater Horizon failed due to buckling. This means that the steel did not have adequate stiffness and therefore it buckled even before yielding. The alternative materials selected must have higher stiffness value than steel. The materials should also have superior mechanical, physical, chemical and manufacturing properties than steel. Using the charts in Figure 7 and 8 below, the following materials can be eliminated from the initial stage of selection because of their relatively low Young’s modulus: polymers, glass, wood/timber, rubbers, foams, plastics and elastomers. Thus potential alternative materials are: composites, metal alloys and metals.

Based on several previous studies, it has been found that the best alternatives for steel are aluminium alloys, titanium alloys and composites (polymer-based) (Bensmina, Menand and Sellami, 2011). Similar findings were also stated by Falther (2017) and Erling (2012). Th properties of these materials are very similar to those of steel (Ahmet and Zehra, 2015; Vadim, 2011). But they are better alternatives that steel because they are more resistant to buckling and are lighter (Arconic, 2017; Wang, 2016). This is also evidenced in Figure 9 and 10 below   

Therefore the three alternatives are compared with steel using weighted property method. The matrix of these materials is a shown in Table 1 below

Table 1: Matrix of steel in comparison with other three alternatives

Performance requirement

Steel

Titanium alloy

Aluminium alloy

Composite (polymer-based)

 

α

β

α

β

α

β

α

β

Stiffness

5

2

5

3

5

3

5

1

Impact strength

5

1

5

2

5

1

5

2

Fatigue resistance

4

1

4

3

4

2

4

3

Lightweight

2

1

2

4

2

5

2

6

Thermal resistance

3

3

3

2

3

1

3

2

Vibrational resistance

4

1

4

1

4

1

4

1

Machinability

2

1

2

1

2

2

2

3

Corrosion & erosion resistance

3

1

3

2

3

1

3

2

Cost

2

6

2

1

2

10

2

1

Durability

3

4

3

4

3

3

3

1

Table 2: Performance indices

Performance requirement

Steel

Titanium alloy

Aluminium alloy

Composite (polymer-based)

Stiffness

10

15

15

5

Impact strength

5

10

5

10

Fatigue resistance

4

12

8

12

Lightweight

2

8

10

12

Thermal resistance

9

6

3

6

Vibrational resistance

4

4

4

4

Machinability

2

2

4

6

Corrosion & erosion resistance

3

6

3

6

Durability

12

12

9

3

 

51

75

61

64

From the values of performance indices in Table 2 above, the best alternative material for steel is titanium alloy. Therefore titanium can be combined with another material to form a titanium alloy that will have superior performance requirements of the drill pipe than steel. The specific materials to be added to titanium have to be chosen after gathering data about the working conditions or environment of the drill pipe.

Comments on requirement for additional information or additional investigation

Additional information or investigation regarding materials selection is required. First, various tests have to be performed on titanium specimens so as to establish its exact mechanical, physical, chemical and manufacturing properties. Second, data has to be collected so as to know the environment in which the titanium alloy drill pipe will be used. Third, other materials that will be added to titanium to make titanium alloy should be determined through an appropriate product design process. The materials have to be selected based on their properties and compatibility with titanium. Fourth, a prototype of representative drill pipe made from the titanium alloy material should be manufactured. Last but not least, the prototype has to be tested and analyzed through computer simulations and FMEA processes.  

Recommendation of suitable materials for the “shut-off valve” (based on certain assumptions)

The suitable materials for the shutoff valve are titanium alloys. The mechanical, physical, chemical and manufacturing properties of titanium alloys make them suitable for use in drilling operations instead of using components made of steel. One of the major performance requirements of the shut-off valve is high stiffness or resistance to buckling. Titanium alloys possess this very crucial property and therefore it can perform perfectly in conditions of high and fluctuating pressure. The materials only buckle after reaching their yield point, hence the operators will have adequate time to rectify the valve if it shows signs of buckling or any other type of failure.

In general, the key properties of titanium alloys that make them most suitable for the shut-off valve are: high stiffness, high impact strength, superior fatigue resistance, lightweight, high thermal resistance, superior vibrational resistance, high machinability, great resistance to corrosion and erosion, and more durable. Being metal alloys, performance requirements of titanium alloys can still be improved by selecting additional materials based on data obtained from test results of the existing steel shutoff valves and the site or well where component will be used. In other words, properties of titanium alloys can be modified so as to make them more suitable for the intended use.    

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