Mamdouh M. Salama

Effect of Microstructure on Corrosion of Steels in Aqueous Solutions Containing Carbon Dioxide

Abstract The influence of microstructure on the corrosion rate of steels in a carbon dioxide (CO2)-containing aqueous solution was measured experimentally as a function of pH, temperature, and part...

Development of a Predictive Model for Activation-Controlled Corrosion of Steel in Solutions Containing Carbon Dioxide

Abstract Corrosion of steel in carbon dioxide (CO2)-containing solutions is considered a chemical reaction-controlled process. A corrosion rate equation was derived on the basis of fundamental reaction rate theory and compared to empirically determined relationships reported in the literature. The predictive equation was developed as a function of pH, partial pressure of CO2 (PCO2), and temperature. The equation allows the inclusion of other variables, such as flow, impurities, inhibitors, and steel microstructure, through the reaction constant. The application limit for this equation extends to the point where corrosion becomes diffusion-controlled as a result of the formation of stable corrosion products on the steel surface.

Development of a Real-Time Active Pipeline Integrity Detection System

Utilizing the SMART Layer technology as a basis, a real-time active pipeline integrity detection (RAPID) system is developed for built-in in?situ assessment of the health of new and existing pipelines. The RAPID system consists of a sensor network permanently mounted on the host pipeline, portable electronic hardware and diagnostic software. Three moduli, including image display, damage sizing, and corrosion depth, are built into the diagnostic software to help in visualization of the approximate location and the extent of corrosion, and to quantify the corrosion sizing and depth. The main advantages of the RAPID system include: (1) ease of use, (2) ability to provide a well-defined resolution, (3) reliability with self-diagnostic and environmental compensation, and (4) quantified corrosion sizing. To verify the detection capability of the RAPID system, a series of tests have been conducted on a 6.7?m long steel pipe with a diameter of 610?mm and a wall thickness of 7.14?mm with ten different types of corrosion flaws. Test results demonstrated that the depth detection limit could be as low as 0.125?mm for general corrosion with an area of 60?mm ? 60?mm under laboratory conditions, while a pinhole with 6.35?mm diameter and 3.5?mm depth can be detected with the given sensor density. Some practical issues for field applications of the RAPID system are also discussed.

Mixed-mode stress intensity factor solutions of a warped surface flaw by three-dimensional finite element analysis

Abstract A finite element analysis procedure has been established to calculate the stress intensity factors of a surface flaw with curved crack surfaces and front in a three-dimensional structure under mixed-mode loading conditions. This procedure converts the √r displacement components in the crack tip quarter point elements into the appropriate stress intensity factors of a fully mixed-mode problem. This method has been developed to treat fracture mechanics problems with complex structural and flaw geometries under arbitrary loading conditions. Weld toe surface flaws in an offshore structural tubular joint have been analysed and their K I , K II and K III solutions are presented. These analysed flaws have curved crack surfaces, and their crack fronts are semi-elliptical when the curved crack surfaces are mapped into flat surfaces. The solutions indicate that, when the structural geometry is complex, the crack tip behavior can be predominantly mixed-mode, even if the loading condition is simple. They also demonstrate that, for a fully mixed-mode problem, a multicomponent contact algorithm is required to prevent crack surfaces from penetrating each other in a finite element analysis.

Influence of grade on the reliability of corroding pipelines

This paper focuses on a comparative analysis of the reliability associated with the evolution of corrosion between normal and high-strength pipe material. The use of high strength steel grades such as X100 and X120 for high pressure gas pipeline in the arctic is currently being considered. To achieve this objective, a time-dependent reliability analysis using variable Y/T ratios in a multiaxial finite strain analysis of thin-walled pipeline is performed. This analysis allows for the consideration of longitudinal grooves and the presence of companion axial tension and bending loads. Limit states models are developed based on suitable strain hardening models for the ultimate behavior of corroded medium and high strength pipeline material. In an application, the evolution of corrosion is modeled in pipelines of different grades that have been subjected to an internal corrosion inspection after a specified time which allows for a Bayesian updating of long-term corrosion estimates and, hence, the derivation of annual probabilities of failure as a function of time. The effect of grade and Y/T is clearly demonstrated.

Application of Composites to Deepwater Top Tensioned Riser Systems

As offshore exploration and production activities head to deeper water, extensive efforts have been focused on mitigating the potential challenges associated with deep- and ultra deep-water riser systems. Such challenges include overcoming the hydrostatic stresses associated with the increased length of water column as well as the increase in overall riser system weight. The implementation of composites in offshore applications is perceived as a promising path forward with composite materials offering many advantages including high specific strength and stiffness, lighter weight, enhanced corrosion resistance, high thermal insulation, improved structural damping and favorable fatigue performance characteristics. This paper focuses on evaluating the potential of composite materials for applications to deepwater top tensioned riser systems from the standpoint of possible impact on overall system cost and reliability. Many deepwater development concepts utilize top tensioned production riser systems, mainly, for conveying production fluids from the wellhead to the surface processing facilities in a dry tree based field development solution. Top tensioned risers can be configured as dual or single barrier systems and can either be hydraulically or hydro-pneumatically supported as on a typical TLP system or pneumatically supported through positively buoyant air cans as on a Spar riser system. Many advantages can be derived from the use of composites on buoyancy can systems. Such advantages include a reduced system weight, higher net lift, smaller diameter cans, improved efficiency and a positive impact on required inspection frequency. Main advantages of using composites for an entire TLP riser system include a significant reduction in both tension requirement and tensioner weight resulting in substantial reduction in total deck loads. An overall assessment of the economic and structural impact of using composites as an alternative to steel will be presented for riser systems and riser system components of both deepwater development concepts.Copyright

Reliability of Burst Limit States for Damaged and Corroded High Strength Pipelines

High strength steels (X100 and X120) that are being considered for high pressure gas pipelines differ from conventional steels by exhibiting lower work hardening capacity, lower strain to failure and softening of their HAZ. These differences impact burst limit state and tensile limit state, in addition to crack arrest. In this paper, the impact of the variations in mechanical properties on the reliability of pipe limit states involving ductile burst of damaged or corroded pipe is examined. The paper presents the results of burst limit state analysis using state-of-the-art plastic burst models of strain hardening pipe and considering all the uncertainties that impact the margin of safety of pipes subject to internal pressure. Intact pipes, corroded pipes and externally damaged pipes are considered. A case study comparing the differences between normal strength (X60) pipeline and high strength (X100) pipeline is also presented.Copyright

Evaluation of Aluminum-Sprayed Coatings for Corrosion Protection of Offshore Structures

Selection of an optimal corrosion protection method for offshore structural high-strength steel was necessary to avoid potential fatigue and hydrogen embrittlement problems. A study to evaluate the corrosion protection provided by sacrificial anodes and flame-sprayed aluminum coatings was undertaken. Reliability, availability, and influence on fracture and fatigue properties were the main factors considered in the study. The results illustrated that a properly applied flame-sprayed aluminum (FSA) coating represents the most viable scheme for providing long-life corrosion protection and improved corrosion fatigue and cracking resistance.

An assessment of strain-aging effect on weldable offshore structural steel

During the fabrication of offshore structures, the steel plate condition changes from the as-received normalized state to a strain-aged state. This paper assesses the effect of 5% prestrain and aging at 250/sup 0/C (482/sup 0/F) for 1 hour on the mechanical properties of normalized low-alloy BS 4360-50D steel plates obtained from two different suppliers. For both plates, strain aging led to an increase in yield strength, ultimate strength, Charpy and crack opening displacement (COD) transition temperatures, and fatigue resistance. The results of fracture toughness tests show that the degree of sensitivity to strain aging may depend on the type of test used; therefore, a test that more closely simulates offshore loading conditions, such as a COD test, is most appropriate. The paper also shows that the impact of strain aging on the integrity of offshore structures is minimized by the competing effects of lower fracture toughness and slower crack-growth rates.

Assessment of Pipeline Integrity Based on Successive Inspection Data

The ultimate objective of performing in-line inspections (ILI) in pipelines is to obtain data to use in establishing the current and future integrity of a given pipeline system. The estimation of the progress of corrosion based on successive inspections in time is preferred to a purely empirical approach providing that the ILI inspection uncertainties are considered in the analysis. This paper provides recommended treatments for assessing the remaining life of a pipeline and proposes a simple yet consistent model that allows the use of ILI data in predicting the future state of a pipeline based on the results of multiple ILI inspections and accounting for the ILI uncertainties.Copyright