In this work, we review and present some recent trends in sour fluid permeation testing of thermoplastic pipes used in oil and gas applications such as thermoplastic liners and reinforced thermoplastic pipe (RTP). The qualification requirements from a permeation standpoint at material and pipe level are discussed including some recently developed test methods and procedures for sour multiphase fluids including water. We also provide a summary of key findings from recent projects on permeation testing of CO2 and H2S through different thermoplastic resins spanning the commodity, engineering, and high-performance polymer grades as well as multilayer pipe walls at select temperatures and pressures. The work also treats the use of small-scale permeation data to predict performance at pipe level and the validation using full-scale tests on pipe sections.

Polyethylenewith a molecular weight greater than a million g/mol,is of increasing commercial interest because it provides a route tomake fibers and films that have unprecedented mechanical properties.The unique properties are attributed to the chain alignment of thelong molecules packed in the orthorhombic unit cell. The anisotropicorthorhombic unit cell, which has weak secondary interaction planes,is prone to slip under a constant load and increasing temperature,thereby restricting the life expectancy of a product. Recent advancesin polymer synthesis have allowed us to tailor the molecular weight,molecular weight distribution, and the entangled state between crystallineregions of the semicrystalline polymer using a single-site catalyticsystem via homogeneous and heterogeneous routes. The decrease in theentanglement network in the polymer has opened the possibility ofsolid-state processing of the nascent powder, thus providing an economicaland sustainable route to make films with oriented chains in the drawdirection. In this paper, we aim to link the creep response of thesolid-state processed tapes made from low-entangled ultrahigh molecularweight polyethylene (UHMWPE) with the entangled state and molecularweight. Our observations are that compared with the Ziegler-Natta-synthesizedUHMWPE polymer, and all polymers synthesized using a single-site catalyticsystem show significantly low creep rate. The commercial tape preparedusing entangled UHMWPE shows a higher creep rate in comparison withthe tapes made of the synthesized low-entangled UHMWPE, which indicatesthe adverse effect of the higher entangled state in addition to thelow M (n). The higher creep rate of the commercialtape can be attributed to higher segmental mobility of the noncrystallinedomain, as determined by solid-state NMR, whereas the tapes made fromlow-entangled UHMWPE showed a constrained noncrystalline domain. Wheneither catalytic system is used, the creep rate is found to decreaseas a function of the molecular weight. Strong dependence of the creeprate is found for polymers having M (n) valuesbelow 1.5 x 10(6) g/mol, while above this threshold,it is not significantly affected. A (linear) dependence of the creeprate on the M (w) and M ( z ) of the polymer used to make the tapes isfound.

A Life Cycle Assessment (LCA) analysis was conducted to compare the carbon and energy footprint of several non-metallic composite pipes and carbon steel (CS) pipes used in onshore sour oil and gas (O&G) production flowlines, based on a specific deployment case (cradle-to-gate scenario). This work provides a systematic approach to assessing the carbon and energy footprint of fiber reinforced thermoplastic/thermoset pipes used in the O&G industry, while also accounting for the end-of-life recycling at the material phase, through the use of the recycled-content allocation method. The impact of corrosion allowance (CA), commonly used at design phase of CS pipes, is explicitly included and discussed. From the raw material extraction to the installation phase, all non-metallic pipe technologies assessed in this study were found to have a lower carbon and energy footprint than CS pipes. The reduction in CO2 emissions can reach up to 60% while the energy footprint can be reduced by up to 50%. The material phase, particularly the composite layer for non-metallic pipes, was found to be the main contributor to the product footprint for all pipe technologies and any optimization in this phase could translate into a significant reduction in the overall CO2 footprint of the pipe. The manufacturing phase is the second largest contributor to the emissions and was found to be (on average) five times bigger for CS pipes than any of the non-metallic pipe technologies assessed in this study. The use of stronger and lighter fiber reinforcements (e.g., carbon fibers) to substitute conventional glass fibers in RTP pipes enabled a noticeable reduction in the product weight. However, the potential in reduction of overall emissions was outweighed by the exceedingly high carbon intensity of carbon fibers. The results of this study are supporting an ongoing strategy for mass deployment of nonmetallic pipes (a traditional driver in reducing operating costs) and provide a path for cleaner production and distribution of hydrocarbon resources. The conclusions of this work could be further developed by accounting for the operational phase of the pipes in question.

Hydrogen Induced Cracking (HIC) in carbon steels is a well-studied mechanism, where diffusing hydrogen atoms accumulates at the steel imperfections/laminations to create gaseous hydrogen with very high pressure, leading to initiation and growth of internal cavities, so-called HIC. Measurements of relevant fracture toughness properties of non-HIC resistant steels in hydrogen environment is critical to predict and assess the initiation and growth of HIC. The present work attempts to quantify the effect of hydrogen on the fracture toughness properties (K-Q and CTOD) of an API X42 pipeline steel under simulated H2S in-service conditions. The fracture toughness properties are measured in TL and SL directions: perpendicular and parallel to the pipeline wall thickness, respectively, following ASTM E1820, standard. Since the X42 is a non-HIC resistant steel, the measurement of the fracture toughness properties in the SL direction is more relevant in terms of HIC initiation and growth than fracture toughness properties in the TL direction. Indeed, parallel to the thickness of the pipeline wall, X42 steel shows microstructural features prone to HIC formation and growth. Steady state H2S in-service conditions were simulated by charging the specimen for 48 h using a special electrolytic solution and then tested (ex-situ) to evaluate the fracture toughness properties. The steady state H2S environment was obtained by measuring the Hydrogen Concentration (CH) in the bulk of the specimen, using Thermal desorption Spectroscopy at three levels of CH. It was observed that the K-Q was not affected in the SL direction, while it was reduced in the TL direction for 1.5 ppmw of CH. The CTOD showed mixed results in the TL direction while it was significantly reduced in the SL direction reaching a saturation at 1 ppmw of CH. Besides, microstructural analyses showed that the presence of inclusions coalescence in form of dimples promote the early failure, which is more pronounced in the hydrogen environment especially at higher levels of CH. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

A single channel Acoustic Emission (AE) system to detect Hydrogen Induced Cracking (HIC) growth in steel structures was developed. The system consists of a commercial AE sensor and an in-house built data acquisition and processing unit. The system is designed for industrial applications, and can be permanently installed on assets operating in sour environments to detect the growth of HIC, and to qualitatively indicate its rate of growth. Previous literature has been able to discriminate HIC-related AE events from other events captured during failure, and has shown that the energy and duration of the AE events can be used for HIC detection. The system developed here was tested in a laboratory where HIC was induced in HIC-susceptible steel coupons. The experimental setup considered here overcame previous limitations, and produced representative test settings that simulate realistic field conditions. Preliminary Ultrasonic Tomography (UT) results, combined with a filtering method from the literature were promising but not conclusive. Additional testing is being conducted to enhance the accuracy and reliability of the measurements.

A previously published empirical model for the prediction of internal pitting corrosion rate (PCR) was assessed to predict maximum PCR in wet sour crude Saudi Arabian transmission pipelines. Although, the original model did not capture actual PCRs, it succeeded to properly rank the selected pipelines by order of increasing PCRs. Two reasons were identified as the main source of discrepancy, namely, the corrosion mitigation availability and the flow-induced localized corrosion. The original empirical model was modified by introducing two correction factors. These correction factors were elucidated through numerical optimization and were based on delineating the contributions of each correction factor. Introduction of the correction factors significantly increased the agreement between predictions and field measurements.

Standard-compliant measurement of the in-plane fracture toughness of metals is often challenging due to insufficient material in the through-thickness direction to extract a full single edge bending (SEB) or compact tension (CT) fracture specimen. In the present work, we propose a new specimen design methodology to overcome this challenge. A W-shaped SEB specimen (called W-SEB) was developed, and its topology was optimized using finite element simulations. The new specimen design was validated numerically and experimentally on a case study showing excellent agreement with standard ASTM E1820 actual SEB specimen geometry. In view assessing the anisotropy of the fracture toughness (KQ and crack tip opening displacement (CTOD)) of pipeline steels susceptible to hydrogen-induced cracking (HIC), the W-SEB specimen was tested on X65 and X42 pipeline steel samples taken from the field. Experimental results show an increase in the maximum CTOD along the in-plane direction as compared to the transverse direction for both steel grades. Such experimental results could lead to important considerations with respect to accurate fitness for service assessment of HIC-damaged assets.

The present manuscript reviews state-of-the art models of hydrogen-assisted cracking (HAC) with potential for application to remaining life prediction of oil and gas components susceptible to various forms of hydrogen embrittlement (HE), namely, hydrogen-induced cracking (HIC), sulfide stress cracking (SSC), and HE-controlled stress corrosion cracking (SCC). Existing continuum models are compared in terms of their ability to predict the threshold stress intensity factor and crack growth rate accounting for the complex couplings between hydrogen transport and accumulation at the fracture process zone, local embrittlement, and subsequent fracture. Emerging multiscale approaches are also discussed, and studies relative to HE in metals and especially steels are presented. Finally, the challenges that hinder the application of existing models to component integrity assessment and remaining life prediction are discussed with respect to identification of model parameters and limitations of the fracture similitude, which paves the way to new directions for further research.

The effect of hydrogen on the fracture toughness properties of an API X65 pipeline steel is studied under simulated H2S in-service conditions. The fracture toughness properties are measured in LT and SL directions (perpendicular and parallel to the pipeline wall thickness, respectively), following ASTM E1820. Due to size restrictions of standard single edge notch bending (SEB) specimens at the direction parallel to the thickness of the pipeline wall, an experimental protocol (see the patent) was developed to carry out the fracture toughness tests, while complying with ASTM standard 1820. This approach is especially useful in situations where hydrogen induced cracking (HIC) and in a broader sense, stepwise cracking takes place, since these cracks initiate and grow primarily in planes parallel to the pipeline rolling plane. Such values of fracture toughness are often different from those commonly measured in planes perpendicular to the rolling plane. Hydrogen might not have the same effect on fracture toughness properties as measured in different directions, due to micro structural features which are inherent from steel manufacturing process. The steady state H2S in-service conditions are simulated by electrolytically charging the specimen, for 48 h and then testing (ex-situ) the specimen for evaluating the fracture toughness properties. The steady state H2S environment charging was obtained by measuring the hydrogen concentration in the bulk of the specimen through thermal desorption spectroscopy (TDS) at three levels of hydrogen concentration. It was observed that the KQ was moderately decreased with increasing hydrogen concentration in the bulk of the steel, while CTOD0 showed a significant reduction with increasing hydrogen concentration. (C) 2018 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.

A finite element analysis is proposed to study the effect of specimen dimensions on lateral diffusion of hydrogen during hydrogen permeation flux measurements. The error of measurement on thick specimens because of 1D diffusion approximation may be as much as 70%. A critical condition for accurate measurements is to designate the area of hydrogen monitoring/exit surface smaller than the area of hydrogen charging/entry surface. For thin to medium thickness specimens (ratio of thickness to specimen radius of 5:10 and below), the charging surface should be maximized and the monitoring surface should be minimized. In case of relatively thick specimens (ratio of thickness to specimen radius above of 5:10), use of a hydrogen-diffusion barrier on the specimen boundaries is recommended. It would completely eliminate lateral losses of hydrogen, but cannot eliminate the deviation towards 2D diffusion near the side edges. In such a case, the charging surface should be maximized and the monitoring surface should be as closer in dimension as the charging surface. A regression analysis was carried out and an analytical relationship between the maximum measurement error and the specimen dimensions is proposed.

In this paper, we studied the water transport in thermoset matrices. We used Fourier Transform Infrared analysis (FTIR) during sorption/desorption experiments to investigate the interaction between sorbed water and the epoxy network. Our results demonstrated that the polymer matrix undergoes hydrolysis. We found that the chemical species involved in the reaction process was the residual anhydride groups. These results support the physical basis of the three-dimensional (3D) diffusion/reaction model. We finally showed that this model is able to reproduce multi-cycle sorption/desorption experiment, as well as water uptake in hybrid metal/epoxy samples. We simulated the 3D distributions of the diffusing water and the reacted water.

The present work discusses the influence of specimen dimensions and boundary conditions on the deviation towards 2D diffusion during hydrogen permeation measurements on thick carbon steel plates. It was mathematically found and experimentally confirmed that hydrogen losses through lateral diffusion could significantly affect the validity of laboratory measurements on thick plates, since the common 1D simplification of diffusion equations is no longer valid. Based on a finite element analysis, two options are proposed to minimize the effects of side diffusion on permeation measurements. The first option, which encompasses ISO 17081 criteria, recommends optimum radii for hydrogen charging and extraction surfaces and is valid for a wide range of specimen thicknesses. The second option relies on modification of boundary conditions and consists of applying a hydrogen-diffusion barrier on the specimen side edges. This second option was experimentally tested and validated by means of an oxide layer deposited usi...

NACE MR0175/ISO 15156-2 standard provides test conditions and acceptance criteria to evaluate the resistance of carbon and low-alloy steels to hydrogen-induced cracking (HIC). The second option proposed by this standard offers a large flexibility on the choice of test parameters (pH, H2S partial pressure, and test duration), with zero tolerance to HIC initiation as an acceptance condition. The present modeling work is a contribution for a better understanding on how the test parameters and inclusion size can influence HIC initiation, and is therefore of potential interest for both steel makers and end-users. A model able to link the test operating parameters (pH, partial pressure of H2S, and temperature) to the maximum hydrogen pressure generated in the microstructural defects is proposed. The model results are then used to back calculate the minimum fracture toughness below which HIC extends. A minimum fracture toughness of 400 MPa root mm, at the segregation zone, prevents HIC occurrence and leads to successfully pass the HIC qualification test, even under extreme test conditions. The computed results show that the maximum generated pressure can reach up to 1,500 MPa. The results emphasize that the H2S partial pressure and test temperature can both have a strong influence on the final test results, whereas the influence of the pH of the test solution is less significant.

A simplified 2D axisymmetric model and a comprehensive 3D weld pool model, accounting for the free surface deformation and the filler metal addition, have been developed to investigate the factors that lead to asymmetric bead shapes in horizontal GTA welding of stainless steels. Buoyancy-induced flow and the sagging of the pool free surface, under the action of gravity, are found to be responsible for the weld asymmetry and the decrease in the weld penetration at the bottom sidewall. The numerical results clearly emphasized the beneficial role of the Marangoni shear stress in limiting the asymmetry of horizontal GTA welds. An additional experimental investigation showed that the asymmetry in the weld shape can be reduced when placing the lowest sulfur content component at the bottom side.

This paper presents a comprehensive finite element model for the numerical simulation of Hydrogen Induced Cracking (HIC) in steel pipelines exposed to sulphurous compounds, such as hydrogen sulphide (H2S). The model is able to mimic the pressure build-up mechanism related to the recombination of atomic hydrogen into hydrogen gas within the crack cavity. In addition, the strong couplings between non-Fickian hydrogen diffusion, pressure build-up and crack extension are accounted for. In order to enhance the predictive capabilities of the proposed model, problem boundary conditions are based on actual in-field operating parameters, such as pH and partial pressure of H2S. The computational results reported herein show that, during the extension phase, the propagating crack behaves like a trap attracting more hydrogen, and that the hydrostatic stress field at the crack tip speed-up HIC related crack initiation and growth. In addition, HIC is reduced when the pH increases and the partial pressure of H2S decreases. Furthermore, the relation between the crack growth rate and (i) the initial crack radius and position, (ii) the pipe wall thickness and (iii) the fracture toughness, is also evaluated. Numerical results agree well with experimental data retrieved from the literature.

A hybrid 2D–3D model for the numerical simulation of Gas Tungsten Arc welding is proposed in this paper. It offers the possibility to predict the temperature field as well as the shape of the solidified weld joint for different operating parameters, with relatively good accuracy and reasonable computational cost. Also, an original approach to simulate the effect of immersing a cold filler wire in the weld pool is presented. The simulation results reveal two important observations. First, the weld pool depth is locally decreased in the presence of filler metal, which is due to the energy absorption by the cold feeding wire from the hot molten pool. In addition, the weld shape, maximum temperature and thermal cycles in the workpiece are relatively well predicted even when a 2D model for the arc plasma region is used.

A finite element model is introduced in this paper to describe the coupling between the welding arc and the weld pool dynamic in pulsed gas tungsten arc welding. The cathode, arc-plasma and melting anode regions are taken into account. The unified time-dependent model describes the heat transfer, fluid flow and electromagnetic fields in the three regions. The originality of the numerical model is its ability to treat the arc and weld pool time evolution under pulsed current welding in a unified formalism, taking into account eddy current in the weld pool. The case of thin plates with fully penetrated weld pools is also handled.To validate the predictions of the model, an Infra-Red camera is used to film the dynamic of the weld pool surface. Then an image processing algorithm permits to get the time evolution of the weld pool width directly from the film. The numerical model is applied to the 304 stainless steel welding, and the computed results show that the predictions are in fair agreement with the experimental results. (C) 2010 Elsevier Ltd. All rights reserved.