Failure Analysis of Pipelines in the Oil and Gas Industry

Abstract

The term “failure” can be defined as the inability of a part or assembly to perform its intended function. Despite the significant technological advances, failure incidents frequently occur, thus, causing human and financial consequences. The failure analysis is a crucial engineering tool. It aims to avoid similar cases in the future, thereby preventing accidents, reducing economic losses due to stopping plant production and keeping the environment safe. Furthermore, the failure analysis contributes to redesign, solve manufacturing drawbacks, save money and time, and in some cases, prevents fatality and saves lives. Conversely, failures can also improve engineering practices; indeed, through analyzing failures and implementing preventive measures, significant advances have been obtained in the quality of products and systems. Moreover, a beneficial outcome of failure analysis has been improved codes and specifications governing materials, for instance, API, ASTM, and ASME. In the current chapter, the failure analysis methodology will be discussed in detail with practical examples to know how to perform analysis for any failure cases, particularly in the oil and gas industry.

1. Introduction

The term “failure” can be defined as the inability of a part or assembly to perform its intended function [1]. Based on the simple definition of failure, we can understand that the part of the component is considered failed if it cannot perform its function perfectly for any reason, for instance, a change in dimensions, corrosion, fracture, and so on. Sometimes unspecialized think the part to fail must be broken or fractured, but this is not the case. In other words, each fracture is considered a failure; however, not every failure is considered a fracture. A fracture separates parts into two or more species in response to the applied or residual stresses.

The pipeline can expose to thinning due to erosion-corrosion damage; however, it is still in service; thus, the pipeline can be considered to have failed, although it is still in service without leakage. The thinning mechanism is a failure since the pipeline has lost service life. In other words, the pipeline was designed to serve a specific period; however, the thinning damage has shortened its lifetime, which means the pipeline lost some of its lifetime. The high-pressure gas (HPG) pipeline has been subjected to internal corrosion, which led to a localized metal loss. Thus, the HPG pipeline has been converted to transfer oil or low-pressure gas due to the fitness for service, which revealed the remaining thickness cannot withstand the high pressure; thus, the pipeline has lost its function to transfer the high-pressure gas.

Material failure can be divided into four types: distortion or plastic deformation, fracture, corrosion, and wear [1]. It is worth noting that two or more physical failures can occur in the same failed part. The root causes of the failure can be divided into three levels; physical roots, human roots, and latent roots. The physical roots can be divided into four categories: design deficiencies, material defects, manufacturing or installation defects, and service life anomalies [2]. The human roots include inadequate inspection and improper equipment installed. The latent roots are the cultural or organizational rules that lead to the human cause; it is not direct roots. The inadequate inspector training is an example of the latent root, where some companies consider the training courses as additional costs that need to be reduced. These companies fail to recognize that this reduction is reflected in the ability of individuals, leading to catastrophic events due to incompetent persons.

The poor design can play a significant role in some failure cases; for example, the pipeline can be designed with a low spot that accumulates the water and causes corrosion. Also, poor design can create a crevice location which accelerates corrosion in the form of crevice corrosion due to the different concentrations of oxygen inside and outside the crevice. Additionally, material selection can be the root cause of some failure cases, using inappropriate material to serve in a harsh environment.

For instance, of inefficient material selection, using 304 austenitic stainless steel in chloride containing environment can lead to severe pitting corrosion or stress corrosion cracking [3]. Moreover, the manufacturing defects in most failure cases play a significant role in the failure. Thus, these defects act as the origin of catastrophic damage. For example, the lack of fusion of manufacturing defects can be a location for crack initiation or a stress concentration.

Furthermore, environmental change can cause premature or unexpected failure before its lifetime. For example, increasing the fluid velocity inside the pipeline accelerates the corrosion rate through erosion damage. Also, if the pipeline is designed according to a specific value (i.e., max limit) of hydrogen sulfide (H₂S) and carbon dioxide (CO₂), the increase of this limit would lead to anticipated failure mechanisms such as Sulphide stress corrosion cracking and CO₂ corrosion, especially in high-pressure gas (HPG) pipelines. In addition, the change in operating conditions may play a crucial role in the failure of pipelines. For example, increasing the operating pressure beyond the design pressure can lead to overloading damage or corrosion by increasing the partial pressure of the corrosive species such as Oxygen (O₂), hydrogen sulfide (H₂S), and carbon dioxide (CO₂) [4]. Also, the inadequate inspection may lead to failure; for example, performing the visual examination without nondestructive examination (NDE) may skip and ignore fine cracks or internal defects that the visual inspection disables to detect. Moreover, the absence of monitoring has a crucial role in some corrosion cases, where different monitoring methods are used to monitor the corrosion rate in the pipeline, such as the corrosion coupon, sand probe, and bio-probe. Without the monitoring method, assessing the operating condition, especially the fluid corrosivity, is not feasible.

Moreover, human error can play a critical role in failure cases through incompetent persons. For example, after conducting the hydro test for repaired tanks or vessels, and during the drainage of the used water, the responsible person can cause collapse due to rapid drain rate or due to the closing of the vent. Also, the non-drain of the water (i.e., Missing to drain) used in the hydro test can cause catastrophic failure, mainly if the pipeline is not used directly after the hydro test and is left for some time. The hydro test water inside the pipeline with stagnation condition will be suitable for SRB colonies to grow and cause corrosion damage, called microbiological induced corrosion (MIC) [5]. Therefore, the water used in the hydro test must be flushed and entirely drained if the pipeline will be used directly after the hydro test. However, suppose the pipeline will not be used directly after the hydro test; in that case, the pipeline must be mothballed through injection of multifunction chemical which contains a mixture of oxygen scavenger, corrosion inhibitor, and biocide.

Indeed, failure analysis aims to determine the causes or factors that have led to an undesired loss of functionality; this considers the failure analysis’s direct benefit. Also, failure analysis is an engineering tool for enhancing product quality and failure prevention; this considers the failure analysis’s indirect benefit [2]. Furthermore, the failure analysis contributes to redesign, to solve the drawbacks of manufacture, saving money, saving time, and in some cases preventing fatality and saving lives [6].

The failure analysis must be performed based on a scientific base and a standard methodology to identify the damage mechanism and determine the significant root causes; otherwise, the analysis outcome will be unexpressed about the actual root causes. Also, the wrong root causes may accuse factors that are far from playing any role in the failure, thus, taking unsuitable recommendations which can accelerate the failure. The false root causes due to poor and inefficient failure analysis methodology can be likened to accusing an innocent person of murder; however, the real killer is free.

From my point of view, failure analysis in the oil and gas industry, specifically in the offshore environment, is considered a crucial case for the failure analysis society. Since these cases enrich the knowledge and information, thus, saving the marine environment against the consequences of failure and causing disasters such as pollution and marine life death in addition to economic loss. In April 2010, in one of the most significant pipelines containment failure accidents, that is, Deepwater Horizon, it was reported that approximately 3.19 million barrels of oil spilled into the ocean [7] and polluted at least 11,200 km² of seawater [8], which was catastrophic to both the economy and environment.

The crude oil at offshore platforms is transferred to the processing plants onshore through pipelines, which are considered one of the safest and most effective ways to transport oil and gas, security and reliability of the transmission pipeline [9]. There are three types of pipelines: gathering lines, transmission lines, and distribution lines. Gas or crude oil gathering lines exist between a well and a treatment plant or collection point [2]. The offshore pipelines are much more critical due to their operational condition, inspection, repair difficulties, and environmental issue [10]. These pipelines are manufactured from carbon steel. The consequences of pipeline rupture could lead to loss of life, injury, fire, explosion, environmental pollution, economic loss, decreasing capacity, and increasing maintenance difficulty [11].

2. Failure analysis methodology

The standard methodology for the failure analysis will be discussed in detail for each step. Practical cases will support the steps. The following steps are common for most failure cases [2]:

1. Collection of background data

2. Preliminary examination of the failed part

3. Chemical analysis (Sludge–Water-Liquid)

4. Nondestructive testing

5. Mechanical testing

6. Chemical analysis of the material

7. Selection, identification, preservation, and cleaning of specimens

8. Macroscopic examination and analysis

9. Microscopic examination and analysis (electron microscopy may be necessary)

10. Selection and preparation of metallographic sections

11. Examination and analysis of metallographic specimens

12. Analysis of fracture mechanics

13. Determination of failure mechanism

14. Testing under simulated service conditions (special tests)

15. Analysis of all the evidence, formulation of conclusions, and writing the report (including recommendations).

It is worth pointing out that the above methodology steps can be applied to most components in the oil and gas industry, such as storage tanks, pressure vessels, and pipelines. In other words, the above steps can be considered a generic methodology for most facilities in the oil and gas industry. However, in the further discussion for each step, most examples of the practical cases of failure incidents will be confined primarily to the pipelines, whether liquid or gas services, since the book’s topic is mainly concerned with the pipelines. Therefore, it will be helpful to give examples of pipelines specifically.

2.1 Collection of background data

The failure analysis methodology’s first step is collecting the background data. The failure investigation should include gaining an acquaintance with all pertinent details relating to the failure. In this step, the failure analyst acts as the detective who investigates a crime case by collecting all available data since the useless information, according to the operators of the failed part, is considered very important to the failure analyst and can contribute to solving the case. The failure analyst only who can judge the importance of the data.

Preparing a checklist containing all the essential required data and questions you need to ask is recommended to do not to forget anything. The list can include: the drawing or the as-built, history of the anomalies for the failed portion, repair history, history of the service environment (i.e., oil/water/gas/multiphase), pigging schedule, type of pig, whether BIDI or foam pig, water analysis reports, gas analysis reports, and scale analysis reports, in addition to the interview with the persons who are responsible for the operating of the failed portion.

It is worth noting that the failure analyst must be decent and non-offensive during the interview with the persons responsible for the failed part in the field and not accuse or blame anyone; otherwise, most of these persons vanish the important data fearing the blame or the accusation.

2.2 Preliminary examination

The preliminary examination can be divided into two stages; the first is performing a site visit to the incident location before retrieving the failed portion. The site visit to the incident location aims to figure out the actual situation of the whole location (i.e., the platform or the plant), not only the failed portion. In some cases, the preliminary site visit to the failure location of the failed part was the clue. Sometimes, the site visit to the failure location revealed simultaneous works implemented at the moment of the incident; consequently, the root causes are highly believed to be external causes due to these operational activities, not the failed part’s environment. This indicates that the analyst must enlarge the investigation area around the failed part. Gradually narrow it, especially when the damage is external, such as a dent, gouge, and scratch.

The second stage in the preliminary examination is a visual examination of the failed part that depicts the actual condition after the incident without any change. The visual inspection aims to detect abnormal features such as damage morphology, plastic deformation, cracks, thinning, erosion, dents, dimensions change, and scratches. During the visual examination, a magnifying glass can be used [12] to enlarge some significant features of the failed part, such as the origin of the crack, damage morphology, and crack arrest location. Using a ruler or measure tap is recommended to determine the aspects of the failure, mainly in the cracking or rupture incident before movement or cutting the failed part, as shown in Figure 1, which shows the crack’s measurement process dimensions for rupture of 24-inch water injection pipeline.

Figure 1.

Measuring the dimensions of the rupture of 24-inch water injection.

Figure 2 shows a failed 2-inch bleeding valve disconnected from the main line of high-pressure gas (i.e., 1200 psi), and the short nipple connection between the valve and the main line was found in a bent shape. On-site inspection indicated scaffolding had been installed around the failure due to concurrent work to replace an 8-inch water injection line directly above the failed valve. This means that the main reason for a defective valve to bend is that a mechanical tool fell and hit the valve, whereas the failed valve is a free end with no support. This failure case is an ideal example of the importance of on-site inspections at the fault location. Without on-site inspections, investigators will come up with unclear root causes and thus make incorrect recommendations.

Figure 2.

Failed 2-inch bleeding valve due to drop of a mechanical tool.

The visual examination of the failed part must include determining the origin from which the crack or the corrosion started. The origin can be manifested as a bulge, such as the overloading failures, or stress concentration location, such as the sharp edges and weldment. For example, Figure 3 shows the origin of the rupture, which occurred in an 18-inch gas pipeline, where the origin appeared in a bulge shape; the spout-like form (bulge) is indicative of an overloading incident. Eventually, during a visual inspection, failure analysts can use failure morphologies to brainstorm and imagine expected failure cause scenarios.

Figure 3.

Illustrates the origin (bulge) of fast-running ductile rupture of 18-inch oil pipeline.

2.3 Chemical analysis (sludge: water-liquid)

It is a crucial step to obtain a sample from the failed portion directly after the incident. The collected sample can be sludge or liquid. The sludge sample will be analyzed to determine the predominant components, especially in the corrosion failure cases. The scale analysis can provide us with informative data about the damage mechanism. Additionally, samples from debris and water are obtained to perform sulfate-reducing bacteria (SRB) testing to determine the count of sessile and planktonic bacteria in the fluid.

If the predominant compound in the analysis is iron carbonate, the expected damage mechanism is CO2 corrosion. If the iron sulfide (FeS) is the dominant compound, the predicted damage mechanism is microbiologically induced corrosion (MIC) due to the microorganism activity of the sulfate-reducing bacteria (SRB) [13]. If the predominant component is the sand, the expected damage mechanism is erosion damage due to the abrasive particles of the sand. If the main compound is iron oxide, the anticipated damage mechanism will be Oxygen corrosion.

The complete water analysis, iron content, H₂S dissolved, Oxygen dissolved, and CO₂ dissolved are significant parameters in most failure cases, indicating how the environment can be harsh. Chlorides have a detrimental effect on the passive layer, destroying the protection formed by the corrosion inhibitor. Oxygen is one of the corrosive species in any corrosion reactions, which accelerates the corrosion rate; therefore, it is recommended to control the Oxygen dissolved to levels of 10 to 50 ppb (part per billion). With increasing the partial pressure of CO₂, the dissolved concentration in the water increase, thus, lowering the pH and increasing the corrosion rate [14]. Figure 4 illustrates the scale sample collection from a failed 24-inch oil pipeline.

Figure 4.

Collection of scale sample from failed 24-inch oil pipeline.

2.4 Nondestructive testing

Nondestructive testing is a helpful and essential tool in most failure cases. Ultrasonic testing (UT) is often used to measure the remaining wall thickness to calculate the maximum pressure that can be applied. Also, UT is used to detect internal defects, whether base metal or weldment, like porosity, cracks, and laminations. Additionally, UT can give the location and size of the defects [12] and measure the remaining wall thickness, as shown in Figure 5.

Figure 5.

UT Technique (a) calibration of the UT device, and (b) Conducting of UT examination.

The dye penetrant test (PT) is often used to detect the surface cracks and clearly show the damage’s extent, as shown in Figure 6 shows a fine crack in the fillet weld of the 2-inch line of the High-pressure gas. The magnetic particles test (MT) also performs the same function as the PT, detecting surface cracks.

Figure 6.

Crack detected in the fillet weld of 2-Inch HPG line by dye penetrant test (PT).

2.5 Mechanical testing

It is a crucial step among the steps of the analysis to confirm the desired mechanical properties of the failed part according to the specification to facilitate the subsequent steps, especially the stress analysis step. Thus, the tensile test determines the yield strength, ultimate tensile strength, and elongation. Additionally, hardness testing is the simplest of mechanical tests; it can be used to assist in evaluating heat treatment [6]. Furthermore, the impact test is used to measure the toughness of the failed parts in the overloading cases and fracture when the notch or point of stress concentration is experienced in the failure case [15]. The impact test is Mainly used when the failed part operates at low temperature or a mechanical tool hit or falls on it, as shown in Figure 7. It can be concluded that the mechanical tests are considered a verification that the material of the failed part was convenient to the applied stresses or the environment during the in-service period or not, according to the specification and the design criteria.

Figure 7.

Performing impact test for specimen cut from an 18-inch offshore pipeline.

2.6 Chemical analysis of the material

In failure analysis cases, routine chemical composition analysis is highly recommended [6]. The chemical analysis of the material is used to determine the failed part’s chemical composition, the same as the mechanical testing. The alloying elements in the cast alloys are rarely distributed uniformly. Thus, the chemical analysis is considered a verification tool by ensuring that the chemical composition does not deviate from the nominal composition according to specification. The chemical analysis is conducted in the laboratory using the optical emission spectrometer. The deviation from the nominal composition at a specific location of the failed part is called segregation [2]. Table 1 illustrates the deviation of the chemical composition of 2205 duplex stainless steel pipe using X-Ray Fluorescence (i.e., XRF) device as shown in Figure 8, which caused a premature failure and gas release [16].

Element	C	Mn	Si	P	S	Ni	Cr	Cu	Mo	N
Pipe	0.013	0.8	0.61	0.038	0.001	4.69	22.5	0.06	3.49	0.06
ASTM A790 2205	0.03	2	1	0.03	0.02	4.5–6.5	22–23	…..	3–3.5	0.14–0.20
Flange	0.022	1.18	0.44	0.035	0.001	5	22.3	0.11	3.72	0.07
ASTM A182 F51	0.03	2	1	0.03	0.02	4.5–6.5	21–23	—	2.5–3.5	0.08–0.20

Table 1.

Chemical composition of 2205 Duplex stainless steel pipe.

Figure 8.

Performing chemical analysis for the weldment using XRF.

In some cases, it is difficult to perform the chemical analysis in the laboratory; therefore, positive material identification (PMI) is a prompt tool that can be used in the field to identify the material with the chemical compositions of the alloying element. The PMI is a portable device used to determine the chemical composition of the material without needing to transfer the sample to the laboratory. For example, Figure 9 shows embrittlement in the flare of low-pressure gas, where the burner’s designed material is 310 stainless steel; however, the PMI analysis revealed that the material is 384 stainless steel. This case shows the importance of the PMI and how it can facilitate determining the clue in the field without needing the laboratory.

Figure 9.

Embrittlement of flare due to unsuitable material.

2.7 Selection, sectioning, preservation and/or cleaning of specimens

In my view, the steps of selection, cleaning, and preservation are very critical and crucial since any fault can destroy the fracture surface, thus, making the failure analysis process difficult, and the root causes may not be present in the actual failure. The significant and valuable portion of the failed part is the origin, whether it is cracking or corrosion damage. The origin (i.e., the start point of the failure) is the clue of most failure cases since it would contain a defect, and the damage starts. Figure 10 shows the locations to be cut for examination (i.e., mechanical testing, chemical testing, macro examination, and micro examination). The proficiency of the failure analyst is shown in the selection of what specific portions are to be studied. Since the whole failed part is not used in the analysis, small selected specimens, such as the origin, are expressed and valuable.

Figure 10.

Selection of location to be cut and studied.

Furthermore, the sectioning step of the selected portion must be performed far enough from the failure’s origin to prevent destroying it, which could lead to false conclusions [2]. During the sectioning process, it must be considered the sample size to be suitable for macro and micro examination and optical and scanning electron microscopes, respectively. It is recommended to use cold cutting techniques for sectioning the samples, like the wire cut and the abrasive blade cutting, which do not introduce any heat to the failed portion, thus, preventing any alteration to the actual condition, as shown in Figure 11.

Figure 11.

Cutting machine with cooling system.

Moreover, handling the selected portion of the failed part is a significant step. Therefore, the selected samples are stored in special boxes made from plastic to avoid friction between the specimens and the container. It is recommended to coat the pieces with grease or apply a removable coating of oil or plastic compound to prevent further interaction between the cut samples and the surrounding environment [12]. The surrounding environment causes corrosion and oxidation to the specimens and confuses whether the source of this corrosion is due to an in-service environment or not.

The cleaning process of the specimens is a crucial step since improper cleaning can destroy the fracture surface. The cleaning process aims to remove corrosion products, debris, and grease from the fracture surface. The cleaning process is an inevitable step in the microscopic examination, particularly when the scanning electron microscope is used. The cleaning program must be started with soft tools and gradually increase to aggressive cleaning tools based on the surface condition. Many cleaning methods can be used in the preparation of the samples. For instance, using the soft hair artist’s brush as a preliminary step, and then using one or more methods from the following: using inorganic solvents, either by immersion or by jet, acetone or alcohol, cellulose acetate tape, replica, and use the ultrasonic cleaning bath. The ultrasonic bath is very useful in accelerating the cleaning process, as shown in Figure 12.

Figure 12.

Ultrasonic cleaning for specimen before examination by SEM.

2.8 Macroscopic examination and analysis

The macro examination step is performed after the excellent cleaning of the sample in which the fracture surface becomes clear and free of corrosion products, dirt, grease, and residual species. The stereoscope is the most helpful tool in this step. The stereoscopic viewing has the same scope as visual inspection but is more detailed as typical stereoscopes allow 10X to 70X magnification [17]. The macroscopic examination does not require the fracture surface to be extremely smooth. The cleaning only is sufficient to perform a macroscopic analysis, unlike the microscopic examination (i.e., Optical microscope), which needs a polished surface to produce high contrast between the microstructural constituents.

The macroscopic examination can provide the failure analyst with beneficial information, for instance, the origin of the fatigue crack and secondary cracks, especially the fine cracks that could not be observed during the visual examination. Furthermore, the macroscopic shows a comprehensive view of the failure location compared to that of microscopic examination, thus, helping the failure analyst to imagine the scenario of what happened during the incident. Figure 13 shows a cross-section macrograph of the failed pipe at the seam weld side. The joint configuration of the seam longitudinal weld is a double-V groove weld. A fusion welding process produces the seam weld. It is most likely a SAW process was used due to the considerable penetration depth in one pass (the filling pass). It is also evident that the crack propagated along the HAZ, HAZ/base metal boundary, or the base metal.

Figure 13.

Macrographs across the fracture surface at about 40 cm from the burst origin.

2.9 Microscopic examination and analysis

The microscopic examination is the clue in most failure cases, especially for metallurgical investigation, and is typically performed by the scanning electron microscope (SEM), as shown in Figure 14. The scanning electron microscope is an effective and helpful tool to know what happened during the incident; it looks like a recorded camera of the events of the failure. The scan electron microscope can provide a large magnification ranging from 5000 to 10,000X [6].

Figure 14.

Scanning electron microscope (SEM).

Some fracture modes can be identified according to the microscopic characteristics, where the dimpled morphology indicates ductile fracture due to overloading, and cleavage facets refer to brittle fracture. The striations are the most characteristic microscopic evidence of fatigue fracture. Figure 15 shows cleavage facets at the origin of an 18-inch gas pipeline crack ruptured due to a welding defect. Figure 16 illustrates the quasi cleavage of a fracture surface of an 18-inch oil pipeline, which ruptures in the form of rapid ductile fracture.

Figure 15.

Shows cleavage facets.

Figure 16.

Shows quasi cleavage.

2.10 Selection and preparation of metallographic sections

The metallographic selection and preparation are crucial steps in metallurgical investigation cases. The selected region of the failed part must be chosen to present unique features of the failed part, which are selected for the characterization process. The selection of the samples which would be examined must be carried out carefully since these samples shall be near the edge of the fracture (i.e., around the origin). In other words, the significant sample which provides valuable information is the sample of the failure location. The sectioning of the metallographic specimens should be perpendicular to the fracture surface in edge view. Furthermore, selecting pieces far from the failure region (i.e., undamaged location) is helpful.

The selected specimens for the metallographic examination should be cut with cold manners. The cold cut prevents alteration of the specimens’ microstructure, high precision cut, and deformation-free cutting for various workpiece sizes. Thus, the wire cut machine or the abrasive cut-off wheels are the standard practical methods for cutting the specimens examined in metallography. The samples are cut into small sizes to facilitate the handling and examination processes; these samples are ground using silicon carbide (SiC) foil and paper to produce a smooth surface before polishing.

2.11 Examination and analysis of metallographic specimens

Metallography is defined as the scientific discipline of examining and determining the constitution and the underlying structure of (or spatial relationships between) the constituents in metals, alloys, and materials (sometimes called materialography) [18]. The most common tool in the metallography examination is the optical or light microscope, with magnifications ranging from ~50 to 1000×, as shown in Figure 17. The optical microscope is used to identify the phases, constituents, and precipitations and determine the size and shape of the grains. The high contrast between microstructural constituents in light microscopy mainly depends on the quality of the specimen preparation process. The metallographic examination is also a verification of the heat treatment where the grains sizes are an indication of the heat treatment quality.

Figure 17.

The optical microscope for metallography.

In Figure 18, it is evident that the HAZ at both sides of the joint contains coarse ferrite grains. In addition to the coarse ferrite grains, grain boundary austenite (GBA) has been observed along the grain boundaries of the coarse ferrite. It is believed that the excessive heat input of the welding process resulted in coarse-grained HAZ, which played a role in the degradation of HAZ zones.

Figure 18.

Coarse grain HAZ of 2205 duplex stainless steel pipe.

2.12 Analysis of fracture mechanics (stress analysis)

It is sometimes quite apparent that excessive loading plays a detrimental role in the failure. Noticeable plastic deformation is observed at the failed pipeline due to the overloading, which causes a change in the pipeline configuration from circle to oval shape. Additionally, the stress analysis is performed based on the specifications, standards, and codes, for instance, ASME B31.8, API 579, and ASME 31G.

For the components with very complex shapes and high thermal gradients, a finite-element analysis (FEA) may be performed to estimate the most likely stress level in the failed part. These analyses can stand alone or can be used to help select critical locations for strain gauge attachment. Finite-element calculations can be time-consuming and expensive, but they are necessary for accurately assessing stress levels in areas of the complex geometry of some components. This analysis is almost essential for determining stresses caused by thermal gradients such as those found in welding [6].

Figure 19 shows an offshore pipeline ruptured due to overloading, where the outer surface of the ruptured wall is bowing out, indicating that the pipeline was highly inflated before it bursts. After failure, the surface is still bowing out, meaning that the deformation of the pipe wall was plastic deformation, and the level of stress encountered was very high.

Figure 19.

Shows the topography of the ruptured wall and the wall bow-out.

2.13 Determination of failure mechanism

Determining the failure mechanism is almost the last step in the failure analysis methodology. The failure mechanism is determined based on the main finding of the visual examination, chemical analysis, mechanical testing, macro examination, and micro examination. It is believed that identifying the failure mechanism is easier and faster than determining the root causes of this failure damage. Since in most failure cases, the visual examination is preliminary and sufficient to figure out the failure damage.

Figure 20 shows a failed 4-inch control valve, and from the visual examination, it is clear that the expected damage is erosion-corrosion damage. Figure 21 illustrates scattered pitting at the 30-inch oil discharge header. Based on the damage morphology and operating condition, it is believed that the microbiological induced corrosion (i.e., MIC) is the anticipated damage mechanism due to bacterial activity (i.e., SRB) and according to the cup-shaped damage.

Figure 20.

Erosion at the 4-inch control valve of discharge line.

Figure 21.

Microbiological induced corrosion (MIC) at 30-inch discharge header.

Figure 22 shows a rupture of the 24-inch water injection pipe, where the observed bumps indicate an overload event; visual inspection shows severe thinning due to corrosion damage; therefore, with a working pressure of 1600 psi, the anticipated failure mechanism is Stress corrosion cracking. The corrosion cracking mechanism combines the stress and the corrosive environment [5]. Also, Figure 23 shows a fracture in the 6-inch well flowline, and site visits to the platform show that the tubing is undergoing significant movement; therefore, the damage mechanism is believed to be fatigue damage due to cyclic loading.

Figure 22.

Stress corrosion cracking (SCC) at 24-inch water injection pipeline.

Figure 23.

Crack due to fatigue at 6-inch flow line of oil well.

2.14 Determination testing under simulated service conditions (special tests)

In some cases, simulation of operating conditions or special testing is strongly recommended to understand the effect of the environment on the same material of the failed component. It is important to note that most simulation tests are not feasible or practical because service conditions cannot be achieved, especially in the case of corrosion failure, which is not feasible in the laboratory. In addition, running simulations requires safety considerations, especially in the event of failures that occur under catastrophic conditions, such as overloading high-pressure gas lines. Figure 24 shows pitting and crevice corrosion testing of an undamaged specimen cut from a defective 2205 duplex stainless steel weldment. This test is designed to determine the effect of the chloride (i.e., high salinity) on welded joints operating in harsh high salinity environments. The results show that preferential corrosion of the specimen occurs in the heat-affected zone and near the weld, as shown in Figure 25.

Figure 24.

Pitting and crevice corrosion testing according to STM G-48.

Figure 25.

The specimen after conducting the pitting and crevice corrosion testing.

2.15 Determination analysis of all the evidence, formulation of conclusions, and writing the report

This step is the outcome of all stages in the failure analysis methodology. The main findings depict every step and are discussed and analyzed intellectually and scientifically to prove the damage mechanism and support the believed root causes. Also, all evidence is collected together during the investigation steps to complete the correct scenario about what has occurred.

The analyst’s competence is also reflected in the preparation of the report, especially in the discussion and conclusion. Suppose the inspector has access to extensive laboratory facilities. In that case, best efforts should be made to analyze and discuss the results of mechanical testing, chemical analysis, fracture, and microscopy before formulating any preliminary conclusions [6]. Eventually, in investigations where the cause of failure is particularly elusive, searching for reports of similar cases may help identify possible root causes. Some references to other similar issues are suggested to support the discussion during the discussion.

3. Conclusion

The failure analysis methodology is considered the guide to perfect failure analysis in the oil and gas industry. Failure analysis in the oil and gas industry, specifically in the offshore environment, is a significant case for the failure analysis society. Since these cases enrich the knowledge and information, thus, saving the marine environment against the consequences of failure and causing disasters such as pollution and marine life death in addition to economic loss. It is helpful to publish the failure analysis cases and share them with others to enrich the knowledge and experience relevant to the society of failure analysis. The steps of the failure analysis methodology can be summarized as the following:

1. Collection of background data (i.e., Drawing, anomalies, repair history, environment, pigging activities, water analysis reports, gas analysis, and scale analysis)

2. Preliminary examination of the failed part (i.e., a site visit to the failure location and visual examination)

3. Chemical analysis (Sludge–Water-Liquid)

4. Nondestructive testing (i.e., UT, MT, PT, & RT)

5. Mechanical testing (i.e., Tensile test, impact test, & hardness test)

6. Chemical analysis of the material (Using the optical emission spectrometer &PMI)

7. Selection, identification, preservation, and cleaning of specimens (i.e., specimens’ selection, wire cut, abrasive blade cutting, and ultrasonic cleaning)

8. Macroscopic examination and analysis (i.e., using of stereoscope)

9. Microscopic examination and analysis (i.e., Using of SEM)

10. Selection and preparation of metallographic sections (i.e., grinding, polishing, and etching of the samples)

11. Examination and analysis of metallographic specimens (i.e., optical microscope)

12. Analysis of fracture mechanics (i.e., stress analysis and finite element)

13. Determination of failure mechanism (i.e., identify the damage mechanism)

14. Testing under simulated service conditions (i.e., special tests)

15. Analysis of all the evidence, formulation of conclusions, and writing the report (including recommendations).