The Virtual Corrosion Engineer

The conventional corrosion management process consists of defining the expected process conditions, identifying potential corrosion threats, and estimating their likely rate, then using that information to develop mitigation plans and inspection schedules. The Virtual Corrosion Engineer (VCE) project aims to improve this process by utilizing online monitoring data to automate the running of the best available corrosion models and provide a continuously updated dashboard in real time. This paper provides an overview of the VCE, together with a brief discussion of the underlying models for two exemplar damage mechanisms, High-Temperature Hydrogen Attack (HTHA) and Under Deposit Corrosion (UDC) in steam generators.

Simplified HTHA Evaluation Using Larson Miller Parameter Concepts

Researchers have been developing mechanistic approaches describing High Temperature Hydrogen Attack (HTHA) damage for quite some time. Although there are a variety of approaches, all of them make use of describing HTHA as a time and temperature dependent phenomena that is sensitive to methane pressure. HTHA research shows the damage process is a phenomenon that is very similar to creep damage which has an exponential relationship to the applied stress and temperature. Based on these observations, the authors propose an HTHA damage assessment procedure that uses the familiar Larson Miller Parameter (LMP) approach and employs the well-known Linear Life Fraction Rule for evaluating operating condition variations in hydrogen partial pressure and temperature.

From Behavior of Water on Hydrophobic Graphene Surfaces to Ultra-Confinement of Water in Carbon Nanotubes

In recent years and with the achievement of nanotechnologies, the development of experiments based on carbon nanotubes has allowed to increase the ionic permeability and/or selectivity in nanodevices. However, this new technology opens the way to many questionable observations, to which theoretical work can answer using several approximations. One of them concerns the appearance of a negative charge on the carbon surface, when the latter is apparently neutral. Using first-principles density functional theory combined with molecular dynamics, we develop here several simulations on different systems in order to understand the reactivity of the carbon surface in low or ultra-high confinement. According to our calculations, there is high affinity of the carbon atom to the hydrogen ion in every situation, and to a lesser extent for the hydroxyl ion. The latter can only occur when the first hydrogen attack has been achieved. As a consequence, the functionalization of the carbon surface in the presence of an aqueous medium is activated by its protonation, then allowing the reactivity of the anion.

Assessment of High-Temperature Hydrogen Attack Using Advanced Ultrasonic Array Techniques

The ability to measure early-stage high-temperature hydrogen attack (HTHA) has been improved by the use of optimized ultrasonic array probes and techniques. First, ultrasonic modeling and simulations were performed to design a set of array probes. The data was then collected using phased array ultrasonic testing (PAUT) and full matrix capture (FMC) techniques. Damage visualization, characterization, and sizing was completed with PAUT, total focusing method (TFM), and adaptive total focusing method (ATFM) advanced algorithms. The detection and sizing capabilities were initially validated on steel calibration samples with micromachined defects and synthetic HTHA damage. Vessels with suspected HTHA damage were removed from service, inspected with multiple array techniques, and then destructively evaluated for a results comparison with metallographic images. This study concluded that the FMC/TFM/ATFM techniques and algorithms improve detectability, characterization, and sizing of early-stage HTHA damage as compared to PAUT.

Volumetric Damage Modeling of High Temperature Hydrogen Attack in Steel Using a Continuum Damage Mechanics Approach

Hydrogen attack is a degradation phenomenon that affects process equipment operated at elevated temperatures in an environment containing a high hydrogen partial pressure. It has been the subject of numerous studies over the years prompted by damage discovered during routine inspections, or incidents that have occurred in service. As non-destructive evaluation (NDE) techniques have improved, damage is being detected during earlier stages where safe operation may still be possible for some time period. This work focuses on the fitness for service evaluation of equipment containing high temperature hydrogen attack (HTHA) using a continuum damage mechanics (CDM) approach. The model can be employed to assess the loss in load bearing capacity due to damage in the form of widespread micro-fissuring and voids (i.e. up to the point of macro-crack coalescence). Experimental data from literature sources have been used to develop a relationship between damage rate and operational loading conditions. The predictions are compared to field experience to illustrate key aspects of this approach.

Crack Healing of High Temperature Hydrogen Attack Corrosion by Heat Treatment

Crack healing demonstrate as a ability of metal to repair physical damage by restructuring the carbon microstructure. High-Temperature Hydrogen Attack (HTHA) destruction happens when carbon steel equipment is exposed to hydrogen partial pressure at high temperatures. This will result in damage that severely degrades the mechanical properties of carbon steel. HTHA always happen at high-stress area in carbon steel such as a post-weld-heat-treated weldment and bending area in the form of the fissure exerted by methane gas inside the equipment. As more fissures are formed, it leads to form micro cracks and weaken the steel to cause a rupture. HTHA is difficult and challenging to inspect. In this research, the HTHA locations were identified by magnetic particle inspection (MPI) and heat treatment was performed by heating to annealing temperature and slowly cooled in the furnace. The early stages of attack with fissures or even small cracks detected are difficult to detect. When significant cracking detected, the particular point is already at higher possibilities of equipment to fail. Previous research has elucidated that there is a possibility of HTHA crack to reduce if undergoes for heat treatment. Heat treatment implies carbon diffuse into the matrix and hydrogen atoms escape. Therefore, diffusion plays an important part in the healing of HTHA crack as it plays a key role in the HTHA process. In this study, the specimen is 4-inch (10.16 cm) elbow pipe of the pipeline between distillation column and heat exchanger with a wall thickness of 1-inch (2.54 cm) had failed due to HTHA from pipelines which have been operating for 10 years. The failure occurs during operation on the pipelines between distillation column and heat exchanger. The crack length has reduced once the failed part was reheated to the annealing temperature of 850°C and slowly cooled in the furnace. The heat treatment by annealing also can be an alternative for altering the structure of the material in order to achieve desired properties and prepare the situation for further decision making by the process operation responsibilities. The conclusion for this research is to identify HTHA locations and restructure the microstructure of affected carbon steel by heat treatment. Results revealed that cracks length had reduced 3 to 10% by heating the failed pipe to annealing temperature and then slowly cooled for microstructure recover. However, the hardness had reduced and further research should be extended to overcome this problem.