This paper will share some of the collaborative efforts completed within DeepStar® Global Deepwater Technology Development Program as part of Phase XII projects in X500 Drilling, Completions & Intervention committee leading to gap identification, industry standards, and guideline deployment. Selecting safe economical materials for production from the increasingly more important HPHT horizons is a serious challenge because of the required combination of ‘safe and economical’. This challenge is being discussed in the literature as well as the standard writing community at great length. The effort aims at economical materials remaining within safe limits without being overly conservative. It is well known that qualification for sour service has occurred experimentally within a matrix of pH and H2S partial pressure ever since NACE MR0175 was first established some 40 years ago. It has now been recognized within the past 5+ years that it is the H2S concentration in solution which is responsible for the corrosion damage. As the total pressure increases the solubility is no longer proportional to the partial pressure, rather a fugacity correction needs to be applied. As the total pressure still increases further into the realm of 15,000 to 20,000 psi a heretofore not fully appreciated effect occurs in that the high methane pressure reduces the solubility even more than would have been predicted by the fugacity correction alone. Its consequence regarding corrosion, however, is still not well established because testing at these high pressures is, and will be for some time, problematic. This makes it clear that acquiring representative and relevant environmental data for the MSBOD is only part of the task at hand. The realistic translation of field environment to the test environment is the other part. Hence, appropriate physicochemical models for extreme conditions must become an integral part of the development of the BOD. In this environment there are two aspects that need to be vigorously pursued. The qualification procedures for the proposed metallurgy need to be clearly delineated and their relevance demonstrated. Test protocols need to be strengthened and results need to be interpreted statistically for relevance. In this context methods for identifying (system) in situ conditions based on external analytical data will also be critically discussed. A methodology will be proposed whereby the H2S partial pressure on x axis of the familiar pH-pH2S diagram can be displaced by the fugacity based H2S concentration. This will result in a reduction of excess conservatism while maintaining an adequate safety margin. This work was initiated and funded by DeepStar, Global Deepwater Technology Development Program as part of Phase XII projects in the (X500) Drilling, Completions & Intervention Committee.

Pipeline operators often deal with the large numbers of dents that require further consideration, and are required to prioritize these dents for further investigation and repair. Code guidance is clear on the relative severity of dents based on a depth or associated with welds, corrosion, gouging or cracking. It allows the pipeline operators to prioritize their dig lists and limit the number of “investigative digs” by omitting plain and shallow dents. However, the dent depth criterion has limitations, experiences learned in the past have shown that a dent prioritization based on depth alone, may still leave a significant number of dents in the pipeline which may pose a threat, particularly from local static strain and fatigue. In recent years, strain and fatigue analyses have been included in the assessment of severity of dents in order to better prioritize and effectively repair dents which represent a threat to the structural integrity of pipelines. However, strain analyses require tedious calculation of dent curvature at each data point from ILI reported dent profile. When a large numbers of dents require to be prioritized by strain severity, using this detail calculation is impractical. Therefore, a screening methodology is required to reliably identify candidate dents that require detail strain assessment. In this paper, an aspect-ratio based screening methodology is developed and applied to over 7,000 dents reported by an In-Line Inspection (ILI) caliper tool for a 265 miles long pipeline section. A total of 263 shallow dents which could have injurious strain level were identified and ranked for detail strain and fatigue calculations. In-ditch investigation of 20 dents with LaserScan profiling showed that the developed screening methodology provides an effective tool to capture all the dents with strain equal and 6.5% at 95% confidence level.

Pipeline constructed in rocky terrain is vulnerable to damages such as denting, gouging and other mechanical damages. In-line inspection (ILI) of these pipelines often reported several hundreds or even thousands of dents. Although most of these reported dents are well below 6% outside diameter (OD) depth limit as per ASME B31.8, few dents (sharp rock dents) with high strain could pose threat to integrity of the pipeline. Recently, strain-based models have been proposed to assess mechanical damage severity in pipelines. Attempts have also been made to characterize cracking susceptibility in rock dents using the critical strain based ductile failure damage indicator (DFDI) model. The objective of this study is to validate this model using full-scale denting tests conducted at the laboratory. Additionally, validation also extends to against the simplified DFDI model without finite element analysis (FEA). In this paper, the existing ASME strain limit and strain limit damage models are reviewed. The critical strain based strain damage model known as Ductile Failure Damage Indicator (DFDI) is then presented. The theoretical aspect of this model, including early work by Hancock and Mackenzie on strain limit (εf, reference failure strain) for ductile failure, is reviewed. The experimental aspect of material critical strain and its measurement using uni-axial tensile testing are then described. An elastic-plastic finite element analysis is employed to calculate DFDI, which is used to quantify the accumulated plastic strain damage and its susceptibility to cracking, and is validated using six full scale denting tests. Finally, the simplified strain limits for plain dent is proposed and validated.

This paper discusses the integrity of 30” OD pipeline subjected to burst of 24” pipeline located 24’ away. Study discusses the detailed finite element analyses (FEA) of pipeline subjected to the stress waves emanating from the rupture event. Dynamic response of a 30” gas pipe buried approximately 6.5’ deep was studied using ABAQUS, to determine how it may have been affected by the rupture of an adjacent 24” gas pipe. The pressure at the 24” OD pipe was dropped from flow pressure to zero psi in a very short interval to simulate a rupture. Sensitivity analyses were conducted by varying the soil modulus and rupture time duration using 2-D and 3-D approaches to arrive at a consensus. In-addition, nonlinear Mohr-Coulomb based advanced soil constitutive models were also used to establish the effect of the soil behavior with the rupture event. Integrity of the pipeline was established based on the stresses/strains and strain based damage factors. Based on the FEA analyses compared with analytical results, the integrity of the 30” OD pipeline can be established and also qualified as either fit or unfit for the operations. The weight equivalent of TNT required to produce this shock loading was obtained by converting internal energy from finite element model using analytical approaches. Analytical solutions and the results from earlier conducted PRCI work were used to verify the simulation approaches. Amplification of stresses on the buried pipeline by using TNT explosives on the surface was obtained through FEA and correlated using experiments conducted and listed in PRCI work. Coupled Eulerian-Lagrangian analyses were further carried out to simulate the crater formation related to the burst event of the buried pipeline.

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