Carbon Steel Pipe Research Articles

Hydrodynamic parameters affecting flow-accelerated corrosion in elbows

Flow-accelerated corrosion (FAC) is a serious degradation mechanism affecting carbon-steel piping in the secondary coolant systems of nuclear power plants. Many researchers have investigated the correlation between wall thinning and hydrodynamic parameters; however, their relationship remains unclear. In this study, the hydrodynamic parameters influencing FAC in elbow sections were investigated for identifying the locations highly susceptible to FAC. Accelerated FAC tests and computational fluid dynamics (CFD) analyses were conducted on a specimen containing elbow sections. The results revealed that the side of the elbow pipe was the most susceptible to FAC because it experienced the most severe wall thinning. The velocity and vorticity vectors obtained from the CFD analysis were decomposed into axial, circumferential, and radial components within a cylindrical coordinate system to evaluate their effects. We found that all velocity and vorticity components contribute to the rate of wall thinning induced by FAC. Therefore, a combination of velocity and vorticity components should be used as hydrodynamic parameters to characterize FAC-induced wall thinning. Specifically, the circumferential velocity and axial vorticity were identified as dominant parameters influencing FAC in the elbows.

Corrosion resistance analysis of Al2O3-TiO2 composite ceramic coatings on carbon steel pipe surfaces

This study investigates the corrosion resistance of Al2O3-TiO2 composite coatings reinforced with multi-walled carbon nanotubes (MWCNTs) on carbon steel pipe surfaces. Coatings were deposited using atmospheric plasma spraying (APS) and high velocity oxy-fuel (HVOF) techniques. Microstructural analysis revealed that HVOF-sprayed coatings exhibited denser and more homogeneous structures compared to APS-sprayed coatings. Electrochemical tests in 3.5 wt% NaCl solution showed that the HVOF-sprayed Al2O3-13 wt% TiO2-1.5 wt% MWCNT coating demonstrated the lowest corrosion current density of 7.6 × 10−9 A/cm2 and the most positive corrosion potential. Hot corrosion tests in a simulated boiler environment (500°C, 1000 h) revealed that this coating also exhibited minimal weight gain (0.9 mg/cm2) and thickness loss (2 μm). The corrosion rate of the optimal coating was 0.05 mm/year, significantly lower than the bare carbon steel (2.45 mm/year). XRD analysis of corroded samples showed that HVOF-sprayed coatings maintained their original phase composition without detectable substrate corrosion products. The superior corrosion resistance of the HVOF-sprayed Al2O3-13 wt% TiO2-1.5 wt% MWCNT coating is attributed to its optimized composition, dense microstructure, and the reinforcing effect of MWCNTs. These findings provide valuable insights for developing advanced coating solutions to mitigate corrosion-related challenges in the oil and gas industry and other harsh industrial environments.

Texture and surface morphology influence of A106 carbon steel pipe on mechanical properties and corrosion resistance after welding process

The surface morphology influenced the corrosion resistance, which depended on the welding process and its parameters. In this study, we investigated the relevance of the welding process that produces excellent mechanical properties and corrosion resistance, which gives the best working performance for carbon steel pipes that transfer refined oil products in an Iraq oil refinery. AISI 1020-A106 carbon steel pipes are welded using shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW). Electrochemical corrosion tests were performed in 3.5% NaCl and immersion tests in heavy Naphtha at 50, 75, and 100 °C. The results show that retained austenite, ferrite, pearlite, and martensite phases are produced after the SMAW process. In contrast, ferrite, pearlite, and a small amount of martensite are produced after GTAW. The ultimate tensile strength of the SMAW samples was higher than those of the GTAW samples, but the GTAW samples had higher fracture elongation, and all samples had no cracks in the welding area during the bending test. The electrochemical and immersion corrosion rates of the samples welded with SMAW are higher than those welded with GTAW. The corrosion rate increases when the naphtha temperature increases and has a higher and unacceptable value at 100 °C.

Water Separation and Formation of Cells with Differential Aeration as Factors Controlling Corrosion of Steel Pipelines in a Crude Oil Storage Facility

The mechanism causing the dramatic intensification of the corrosion deterioration of carbon steel pipes in a crude oil storage facility has been investigated. This study considers a number of factors affecting corrosion in crude oil, such as the water content, the corrosivity of the aqueous phase, the kinetics of water–oil separation, the effect of dissolved oxygen, the effect of the crude oil quality, the degree of stagnancy inside of the pipes, the possible contribution of microbially induced corrosion (MIC) and the presence of deposits. The key root of the corrosion intensification was the separation of the water phase, supported by stagnancy, which eventually led to the formation of stable shallow pits surrounded by cathodic areas.

Analysis and optimization design of internal pressure resistance of flexible composite pipe

Flexible composite pipes have the advantages of light weight, corrosion resistance, scale resistance, and low cost compared to carbon steel pipes, and have attracted much attention in the application of onshore oil and gas gathering and transportation systems. Understanding the relationship between the pressure-bearing mechanical properties of composite pipes and their structural characteristics is crucial for guiding their process application. To investigate the mechanical behavior of flexible composite pipes under internal pressure loads, discrete and combined finite element models were established to analyze the stress-strain characteristics of flexible composite pipes. The bursting strength was predicted, and the influence of winding angle and number of reinforcement layers on the pressure-bearing capacity of flexible composite pipes was revealed. The applicability of the two models in the analysis of internal pressure resistance of flexible composite pipes was evaluated using whole pipe strain testing and instantaneous hydrostatic burst experiments. The results showed that the reinforcement layer is the main pressure-bearing layer of flexible composite pipes, and the innermost reinforcement layer bears the highest pressure. The pressure-bearing capacity of flexible composite pipes significantly increases when the winding angle is greater than 53°, and the increase in pressure-bearing capacity slows down when the number of reinforcement layers exceeds 3. Under the combination model, the strain and bursting strength of flexible composite pipes were closer to the experimental results. The study clearly defines the stress-strain characteristics of flexible composite pipes under internal pressure load and the impact of process parameters, providing a basis for the optimization design of single well oil transmission pipelines in Xinjiang oilfield.

Effect of seawater salinity, pH, and temperature on external corrosion behavior and microhardness of offshore oil and gas pipeline: RSM modelling and optimization

This research aims to investigate the effects of seawater parameters like salinity, pH, and temperature on the external corrosion behaviour and microhardness of offshore oil and gas carbon steel pipes. The immersion tests were performed for 28 days following ASTM G-1 standards, simulating controlled artificial marine environments with varying pH levels, salinities, and temperatures. Besides, Field emission scanning electron microscopy (FESEM) analysis is performed to study the corrosion morphology. Additionally, a Vickers microhardness tester was used for microhardness analysis. The results revealed that an increase in salinity from 33.18 to 61.10 ppt can reduce the corrosion rate by 28%. In contrast, variations in seawater pH have a significant effect on corrosion rate, with a pH decrease from 8.50 to 7 causing a 42.54% increase in corrosion rate. However, the temperature of seawater was found to be the most prominent parameter, resulting in a 76.13% increase in corrosion rate and a 10.99% reduction in the microhardness of offshore pipelines. Moreover, the response surface methodology (RSM) modelling is used to determine the optimal seawater parameters for carbon steel pipes. Furthermore, the desirability factor for these parameters was 0.999, and the experimental validation displays a good agreement with predicted model values, with around 4.65% error for corrosion rate and 1.36% error for microhardness.

Gauging and Imaging of Pipes using Water-Immersible Ultrasonic Instrumentation System

Abstract The purpose of this research work is to establish the functionality of the novel ultrasonic non-destructive inspection system and accurate gauging of pipes and to locate and visualise flaws in the form of B-Scan cross-sectional view (front-view) of the pipe under test. In this paper, presents a custom-made perspex inspection head assembly integrated with a stand-alone, Li-ion battery-powered and IP67-grade water-immersible ultrasonic instrumentation and gauging system, which enables an efficient assessment of the condition and health of pipes in stringent environments. Extensive inspection was carried out on six samples of 12” Inner Diameter (ID) type carbon steel (CS) pipes with length of 500 mm and having machined wall thickness to simulate loss of wall-thicknesses from 10 % over a length 150 mm of pipe, using 5 MHz spherically focused transducers. Further inspection were carried out on a 12” CS pipe with four notches and four flat bottom holes (FBH) machined on the OD side. Identical flaws were also machined onto 12” CS pipe of total length of 700 mm containing water inside the pipe in flowing condition with water flow rate of 100 litres per minute (LPM). The test results demonstrate the effectiveness of the developed IP67 grade water-immersible ultrasonic pipe inspection and gauging instrumentation system for assessing the condition and health of long-length carbon steel pipes operating in harsh environments.

A novel flaw detection approach in carbon steel pipes through ultrasonic guided waves and optimized transformer neural networks

A novel flaw detection approach in carbon steel pipes through ultrasonic guided waves and optimized transformer neural networks

A Case Study on Caustic Corrosion in Refinery Piping

Caustic soda is received from supplier with concentration about 48% and stored at main storage tank and transferred intermittently to the refinery process unit's neutralization tanks at same concentration. Dilution is taking place at these tanks. In order to prevent caustic soda from freezing and /or crystallization (winterization) in intermittent transferring piping, it was kept warm by means of steam tracing and insulation together.Failure of carbon steel piping by caustic stress corrosion cracking (embrittlement) and caustic gouging has been a recurring problem, several repairs attempts were made without success using patch plates and/or temporary clamps. Some parts were totally replaced with schedule 80 piping but suffer failures within 12 months.Close observation of the corroded locations reveals severe grooving along the length of pipe at 3 & 9 o'clock positions where steam tracing line is touching the pipes due to braking of fixation clamps.Several measures were recommended, these include avoidance of hot spots by steam tracing; avoidance of temperature increase during idle condition and redesigning the distribution piping in order to transfer caustic solution with concentration not more than (33%).

Clathrate Hydrate-Solid Surface Adhesive Shear Strength Measurements on Carbon Steel Surfaces.

Oil and gas flowlines operating in subsea or cold terrestrial environments face the risk of forming hydrate deposits and plugs. The pressure differential across a hydrate plug can cause the plug to detach from the pipe wall and travel through the pipeline, potentially impacting a bend or inline equipment, causing damage or injury to personnel. Therefore, the hydrate-solid adhesive shear strength is of interest in estimating the maximum allowable differential pressure across a plug during depressurization procedures before the plug is likely to detach from the pipe wall. Quantifying the changes in adhesive shear strength with time and operational conditions is essential in estimating the potential of hydrate deposits to slough from the pipe wall. This work used a force meter with a cylindrical "pig-style" probe mounted to a single axis motorized test stand to measure the force required to dislodge model THF structure II hydrate plugs in carbon steel pipes. Profilometry measurements were used to quantify the mean surface roughness and relative peak frequency of the pipe surfaces. Contact angle measurements were performed of a water droplet on pristine, sanded, and corroded pipe surfaces immersed in nonpolar solvents. The adhesive shear strength of the hydrate plugs was measured for different subcoolings, solid surface roughness, and surface wettabilities. Subcooling was shown to impact the hydrate-solid adhesive shear strength, and a mixed adhesive/cohesive failure mechanism was observed at the highest subcooling tested. The surface roughness and wettability were also shown to influence the hydrate-solid adhesive shear strength, with readily wetting corroded and sanded carbon steel surfaces resulting in greater interface adhesive strength than the pristine carbon steel system. This is likely due to a Wenzel wetting mode at the interface, resulting in a higher ratio of actual to apparent wetted area as well as establishing a mechanical interlocking mechanism.

Influence of input variables on the unitary deformation experienced in pipes subjected to the action of lateral loads

The hydrocarbon transportation industry uses extensive pipeline networks subject to complex loading conditions. The finite element analysis (FEA) has proven to be effective in simulating the deformation behavior in these pipelines, which assists in the assessment of their integrity and risks. In this work, a model developed using finite elements is proposed to analyze the behavior of API 5L Gr B carbon steel pipes, subject to internal pressure and lateral loads. The model is validated through uniaxial tensile and four-point bending tests. In addition, parametric analysis is carried out considering variables such as diameter, lateral load, and distance between supports. The objective is to identify which one of these variables has the most influence in the unit strain. The results indicate that the unit strain obtained from the numerical model agrees with the experimental tests. Furthermore, it is concluded that the diameter is the influential parameter.

Zynq SoC FPGA-based water-immersible ultrasonic instrumentation for pipe inspection and gauging

Abstract A re-programmable Zynq system-on-chip (SoC) FPGA-based water-immersible 2-channel ultrasonic instrumentation has been designed and developed and it is mounted inside the IP67-grade enclosures, which is suitable for ultrasonic pipe inspection and gauging applications. The novel, compact Zynq SoC FPGA-based ultrasonic instrumentation system, powered by lithium-ion batteries for its operation over five hours, exhibits its adaptability for challenging environments, including its ability to travel through pipes carrying oil or water. One of the salient features of the 2-channel system is the capability to acquire echo signals using 12-bit/100 MSPS digitizer to provide highly accurate values of the inner diameter (ID) and wall thickness (WT) of the pipe under test. The system has been utilised to acquire and store 256 MB of A-Scan data in the DDR3 memory module of FPGA. Subsequent to five hours of acquisition, data was transferred to the computer to reconstruct B-Scan cross-sectional images for 300 mm nominal bore (NB) Stainless Steel (SS), and Carbon Steel (CS) pipes machined with volumetric and planar standard flaws. The B-Scan images could reveal both types of defects along with the location and size of these flaws. Such ultrasonic instrumentation has become an advanced tool to acquire a large volume of gauging data for pipes operating in harsh conditions, making it a vital asset for the inspection of pipes containing crude oil or processed water for petrochemical and nuclear industries. This paper provides brief details about the ultrasonic PIG instrument, with few inspection results obtained for SS and CS pipes.

Multiphysics Simulation of In-Service Welding and Induction Preheating: Part 2

In-service welding simulations were carried out using a multiphysics finite element analysis (FEA). Calculated data as temperature and thermal cycles were validated by comparing them with experimental welding results carried out in a carbon steel pipe attached to a water loop. Two in-service welding cases were tested using the GMAW-P process with and without the assistance of induction preheating. The molten zone of weld macrographs and the simulated models were matched with excellent accuracy. The great agreement between the simulation and experimental molten zone generated a maximum error in the peak temperature of 1%, while in the cooling curve, the error was about 10% at lower temperatures. A higher hardness zone appeared in the weld’s toe within the CGHAZ, where the maximum induction preheating temperature achieved was 90°C with a power of 35 kW. Induction preheating reduced the maximum hardness from 390 HV to 339 HV.

An Impedance-Loaded Surface Acoustic Wave Corrosion Sensor for Infrastructure Monitoring

Passive surface acoustic wave (SAW) devices are attractive candidates for continuous wireless monitoring of corrosion in large infrastructures. However, acoustic loss in the aqueous medium and limited read range usually create challenges in their widespread use for monitoring large systems such as oil and gas (O&G) pipelines, aircraft, and processing plants. This paper presents the investigation of impedance-loaded reflective delay line (IL-RDL) SAW devices for monitoring metal corrosion under O&G pipeline-relevant conditions. Specifically, we studied the effect of change in resistivity of a reflector on the backscattered signal of an RDL and investigated an optimal range through simulation. This was followed by the experimental demonstrations of real-time monitoring of Fe film corrosion in pressurized (550 psi) humid CO2 conditions. Additionally, remote monitoring of Fe film corrosion in an acidic solution inside a 70 m carbon steel pipe was demonstrated using guided waves. This paper also suggests potential ways to improve the sensing response of IL-RDLs.

Experimental and computational failure analysis of hydrogen embrittled steel cords in a reinforced thermoplastic composite pipe

Reinforced thermoplastic pipes (RTPs) have attracted considerable attention lately in the oil and gas sector as potential alternative to carbon steel pipes. However, some RTP systems have been experiencing failures as a result of deficient design and inadequate operation practices. This study presents a comprehensive assessment of the failure of a steel-reinforced flexible thermoplastic composite layered pipe in a sour environment characterized by hydrogen sulfide (H2S) exposure. Utilizing scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS), the investigation conclusively attributes the failure of the RTP to hydrogen embrittlement of the carbon steel cords and wires in the reinforcement layer. Finite element models at both meso-scale and full RTP scale were developed, incorporating a novel damage initiation and propagation criterion for failure prediction of embrittled and non-embrittled (e.g. ductile) reinforcement steel cords. The numerical models consistently predicted a reduced burst pressures of the hydrogen embrittled case of the RTP, with a close match with field observations. They also predicted failure modes that closely matched the SEM findings, hence highlighting the unsuitability of the existing steel cords in RTPs for use in sour service environments. Additionally, the presence of moisture in the annular space was identified as an exacerbating factor. This investigation provides important insights for the future design and operation of RTPs susceptible to hydrogen embrittlement, paving the way for improved structural integrity and safety measures. Further research avenues may involve modeling hydrogen diffusion in the thermoplastic layers, simulating the movement of moisture in the annulus through the capillary effect, and incorporating fracture toughness degradation for a more thorough understanding of the interplay between mechanical and environmental factors in the hydrogen embrittlement of steel-reinforced RTP composite pipes.

Fracture investigation at 300oC on carbon-steel and austenitic stainless-steel pipes of NPPs under cyclic loads

The Leak-Before-Break (LBB) of high enthalpy piping of Indian NPPs require fracture stability demonstration of pipelines with postulated cracks under design basis earthquake loads. Earlier large number of cyclic fracture and corresponding monotonic fracture tests on large sized pipe components were conducted at room temperature. In current program, monotonic/cyclic fracture experiments are extended to reactor operating temperature (300 oC). The aim of this study is to demonstrate the structural integrity of SA333Gr6 piping and Stainless Steel (SS) 304LN welds under monotonic/cyclic loading which simulates extreme earthquake events and operating temperatures. Total six pipes/pipe welds of carbon steel (8-inch NB ~219 mm outer diameter and 19 mm thick) and SS304LN (12-inch NB~324 mm and outer diameter ~25 mm thick) with through-wall cracks have been tested under four-point bending. Two monotonic fracture tests have been conducted at 300 oC under monotonic loadings. Different experimental results like LLD (Load Line Displacement), Total Load, CMOD (crack mouth opening displacement), Crack Growth values have been obtained. Based on this data the load carrying capacity are obtained for both 8-inch and 12-inch cracked pipes. The cyclic fracture tests have also been conducted at 300 oC under fully reversing cyclic loading on four pipes. Three 8-inch SA333Gr6 pipes have been tested under different magnitude of peak load values. Similarly, one 12-inch SS pipe is also tested under cyclic loading. For carbon steel pipes, the reduction in load capacity is slightly higher under cyclic loadings at 300 oC compared to that at room temperature. However, for stainless steel pipes the load reduction factor at 300 oC is in good agreement with that at room temperature.

The Development of a Laboratory Simulation to Study the Surface Temperature Effect On Corrosion Under Insulation Formation

Corrosion under insulation (CUI) refers to external corrosion that appears between carbon steel piping or pressure vessels’ external surfaces underneath jacketed insulation. There are many factors affecting the CUI corrosion rate. The chance of CUI exhibits a higher value between 50ºC and 175ºC. Understanding the corrosion rate at critical temperatures is important in assessing insulation performance and preparing maintenance plans. It is challenging to predict the CUI rate in a real working pipeline. A laboratory simulation following ASTM G189-07 is a laboratory scale to study and provide an alternative method for determining CUI corrosion rate at a controllable working temperature. At 80ºC, the CUI corrosion rate is lower than the CUI rate at 75ºC. The result shows that the corrosion rate on the carbon steel pipeline is not perpendicular to temperature.

Modeling of necking area reduction of carbon steel in hydrogen environment using machine learning approach

Low carbon and low alloy steel pipes, prevalent in natural gas transmission systems due to their affordability, weldability, and strength, are confronted with significant challenges such as hydrogen embrittlement (HE) when transitioning towards hydrogen energy systems. This necessitates innovative predictive strategies to overcome these hurdles. Most existing research on HE has focused on a limited range of low carbon and low alloy steels under specific experimental conditions and has been constrained by the limitations of experimental facilities. To expand the research scope, our study incorporated seven machine learning (ML) techniques: Random Forest (RF), Decision Tree (DT), Extreme Gradient Boosting (XGBoost), Gradient Boosting (GB), Adaptive Boosting (AdaBoost), Categorical Boosting (CatBoost), and Artificial Neural Networking (ANN). The aim is to predict the HE in terms of the degradation of mechanical properties, specifically the reduction in area. Drawing from tensile test data obtained from 47 distinct low carbon and low alloy steels under pressurized hydrogen gas conditions, we constructed and evaluated a range of ML models, with the aim of identifying the most efficacious one for our study. Our results indicated that the CatBoost ML model offered the best prediction of the reduction in the area of these steels in a hydrogen environment. The CatBoost model provided a low Mean Absolute Error (MAE) of 7.32, Mean Square Error (MSE) of 83.78, Root Mean Square Error (RMSE) of 9.15, and a coefficient of determination (R2) value of 77.62% for the training data and 72.50% for the testing data. Furthermore, the CatBoost model identified hydrogen gas pressure and the steel's ultimate tensile strength as the most influential parameters, contributing 47.4% and 19.2% respectively to the prediction of HE. This research provides valuable insights into the development of advanced materials and infrastructure for efficient hydrogen gas transportation, supporting the broader shift towards a hydrogen-based energy economy.

Benchmarking the impact of nickel filler addition, weld hardness, environmental pH, and corrosion inhibitors on A333 carbon steel pipe weld corrosion

This study addresses the challenge of preferential weld corrosion in ASTM A333 carbon steel piping, investigating the intricate interplay of various factors. The welding process induces microstructural alterations, making affected areas more prone to corrosion, resulting in Preferential Weld Corrosion (PWC). While the addition of 1 % nickel filler shifts the galvanic potential of Weld Metal (WM), its impact on PWC is marginal due to the high rates of its intrinsic corrosion. Notably, nickel filler addition accelerates corrosion in the heat-affected zone (HAZ). In carbon dioxide (CO2) environments, the presence of acetic acid (HAc) intensifies corrosion; yet, the application of morpholine as pH neutralizer effectively counters its effects. Imidazoline based corrosion inhibitor prove successful in PWC mitigation, particularly at elevated pH levels. Furthermore, Post Weld Heat Treatment (PWHT) significantly reduces hardness, aligning with a decrease in corrosion. Of paramount importance, this study not only examining the effects of individual factors, including microstructure, pH adjustment, corrosion inhibitors, and PWHT, but also scrutinizing their combined impacts. The integration of PWHT with pH adjustment and inhibitor injection yields corrosion rates below 0.1 mm/y, ensuring a remarkable 30-year service life even under challenging conditions. This study underscores the necessity of a comprehensive strategy, combining these factors, to effectively manage preferential weld corrosion in carbon steel weldments.

Assessment of flow-accelerated corrosion-induced wall thinning in SA106 pipes with elbow sections

A combination of flow-accelerated corrosion (FAC) tests and corresponding computational fluid dynamics (CFD) tests were performed to determine the hydrodynamic parameters that could help predict the highly susceptible location to FAC in the elbow section. The accelerated FAC tests were performed on a specimen containing elbow sections fabricated using commercial 2-inch carbon steel pipe. The tests were conducted at flow rates of 9 m/s under the following conditions: water temperature of 150 °C, dissolved oxygen <5 ppb, and pH 7. Thickness reduction of the specimen pipe due to FAC was measured using ultrasonic testing. CFD was conducted on the FAC test specimen, and the turbulence intensity, and shear stress were analyzed. Notably, the location of the maximum hydrodynamic parameters, that is, the wall shear stress and turbulent intensity, is also the same location with maximum FAC rate. Therefore, the shear stress and turbulence intensity can be used as hydrodynamic parameters that help predict the FAC-induced wall-thinning rate. The results provide a method to identify locations susceptible to FAC and can be useful for determining inspection priority in piping systems.