ABSTRACT The complexities of most underground pipeline systems and surroundings continue to pose challenges for above ground indirect inspection surveys, and the utility of the acquired data. The result has been gradual loss of confidence in indirect inspection surveys, and subsequent increase in research and development efforts in above ground survey techniques. At the crux of the matter is the following objective: to improve the probability of anomaly detection through effective above ground survey methods, including data acquisition and data analysis. In this paper we have investigated and reported some of the inherent problems of the typical underground pipeline surroundings by simulating these complexities in a lab scale facility. In the experiments, we varied three classes of factors that normally influence conventional pipeline survey data: pipeline features, soil features, and survey features. Our tests revealed that the probability of detection of a given anomaly size can be highly variable with respect to any of these parameters. We also found that difficulties in detecting anomalies is very often linked to the survey methodologies employed – that is, the way the survey was performed, the way the survey data was gathered, and the data analysis method. From lessons learned in this test facility, suggestions are proffered for improving the effectiveness of survey data acquisition and analysis, and of course, increasing the probability of coating anomaly detection and prioritization. INTRODUCTION The level of confidence placed on indirect inspection surveys, namely AC voltage gradient (ACVG), DC voltage gradient (DCVG), and current attenuation, and their associated data, varies widely within the pipeline industry. This sombre reality stems from the uncertainties associated with coating evaluation survey methods and the accompanying field data. But the good news is this: once some realization of the uncertainties or the cause of uncertainties is known, steps can be taken to reduce them, and thus, produce more reliable data that can increase confidence level.
Wang, Jing (Corrosion and Protection Center, Key Laboratory for Environmental Fracture, University of Science and Technology Beijing) | Zhang, Lei (Corrosion and Protection Center, Key Laboratory for Environmental Fracture, University of Science and Technology Beijing) | Xu, Lining (Corrosion and Protection Center, Key Laboratory for Environmental Fracture, University of Science and Technology Beijing) | Lu, Minxu (Corrosion and Protection Center, Key Laboratory for Environmental Fracture, University of Science and Technology Beijing) | Chang, Wei (CNOOC Research Institute) | Guo, Hong (CNOOC Research Institute)
Rodríguez, Sandra (Facultad de Ingeniería UALSP) | Narváez, Lilia (Facultad de Ingeniería UALSP) | Miranda, Juana María (Instituto de Metalurgía UASLP) | Cárdenas, Ángel (Instituto de Metalurgía UASLP) | Espericueta, Dora (Instituto de Metalurgía UASLP)
ABSTRACT The focus of this paper is to examine and review how applications of Electrochemical Chloride Extraction (ECE) affect the mortar mechanical properties. The mortar specimens were prepared with water/cement (w/c) ratio of 0.5 and contaminated with 5% of NaCl by mass of cement. A clean steel rod was centrally embedded in each specimen. The electrochemical treatments were based on different electrical current densities of 1, 3, 6 and 9 A/m2 that were applied for 15 days. The state of corrosion was monitored before, during and after applying ECE regularly for two weeks. Selected samples from the cover zone of the untreated and treated specimens were taken to assess their chloride profiles. According to results of the compressive strength on mortars the mechanicals properties were not affected by ECE. INTRODUCTION For a long time, the most widely used material for construction has been concrete, whose consumption has exceed all building materials put together. Although many people believe that Reinforced Concrete Structures (RCS) do not have any problems of degradation, one of the most important causes of deterioration of these structures is the corrosion of reinforcing steel.1,2 This issue has been of great interest in the last three decades, for the reason that the costs of repairs are extremely high and sometimes higher than their initial construction cost.2 Under normal conditions, concrete is capable of providing protection to reinforce steel against corrosion. It’s because of the high quantity of alkalinity that has a pH in the range of 12.5 to 13.5 in the concrete. In a highly alkaline environment, the steel creates a thin continuous and adherent film on its surface. This thin film prevents the dissolution of the iron itself – this is shown in figure 1.3,4 However, the durability of the RCS can be reduced by a corrosion attack.
ABSTRACT Corrosion monitoring of steel-reinforced concrete structures with embedded sensors require sensor operations lasting several decades. Many corrosion sensors use probes of material similar to the reinforcing metal that require routing electrical wires to the concrete exterior that may degrade or become damaged. Other sensors require electrochemical electrodes that degrade in time or require recalibration. Surface acoustic wave (SAW) sensors have been developed and have been presented for application in corrosion monitoring of steel-reinforced concrete structures. SAW sensors are wireless and require no local power which is promising for extended term durability while embedded in concrete structures. The passive electronic components were designed to be chemically isolated from the environmental exposure by a conformal coating yet still maintain RF signal transmission. An approach to implement SAW sensors and preliminary testing of sensor materials in concrete environments are presented. INTRODUCTION Reinforced concrete in severe environments with exposure to chloride, carbon dioxide, and sulfates for example can result in corrosion deterioration with subsequent consequences in serviceability of the structure and increased maintenance costs. In the United States, an estimated cost of corrosion was approximately $8.3 billion annually in direct costs for highway bridges 1. As such, a need exists to assess corrosion maintenance requirements and improve upon current inspection practices. Corrosion monitoring of steel-reinforced concrete structures with embedded sensors would complement common corrosion inspection methods. Indeed in certain situations such as in bridge internal post-tensioned ducts and tunnel applications where access is limited or restricted, in-situ monitoring systems may become a vital inspection tool. However, embedded sensors in these situations would require sensor operations lasting several decades. Many corrosion sensors use probes, of material similar as the reinforcing metal, that require routing electrical wires through the concrete cover to the structural component exterior that may degrade or become damaged by weather or vandalism 2.
ABSTRACT Reinforced concrete pipes are commonly used for culvert and storm drainage applications and are intended to last for several decades. The effect of cracks on corrosion of embedded reinforcing ~3/16 in (~4.75 mm) diameter steel wires was investigated. Cracks having a nominal width of 0.02 and 0.1 inch (~ 0.5 and ~2.5 mm) were induced by 3-point bending on the interior surface of quadrants extracted from 18inch (45 cm)-diameter concrete pipes. Two types of concrete pipes were examined and referred to as Z-type and R-type with average interior concrete covers of 1.2 and 0.7 inch (30.5 and ~17.8 mm) respectively. The Z-type contained higher cement content whereas the R-type had a 20 % fly ash replacement. The cracked specimens along with controls were tested under both continuous and 1 week-dry/1 week-wet cyclic exposures to 500 ppm chloride solution for periods of 115 days and 7 cycles respectively. Open circuit potential and electrochemical impedance measurements were performed. Electrochemical test results were calibrated using data obtained from destructive examination of wire corrosion. Data analysis showed that corrosion current increased as the crack width-to-cover ratio increased for both types. Corrosion-based projection models indicated strongly enhanced performance for the 0.02-inch (~0.5 mm) cases compared to the 0.1-inch (~2.5 mm) cases. INTRODUCTION Reinforced concrete pipes (RCP) are widely used in installations requiring service over a period of many decades, so only extremely slow deterioration with time can be accepted. Concrete cracks are often revealed by inspections conducted on recently placed pipes. In-place RCP cracks can degrade pipe performance by decreasing structural strength and dimensional stability, permitting leaks and marginally increasing hydraulic resistance, and by allowing premature corrosion of steel reinforcement.1- 3 At the bottom of such cracks bare steel is likely to be directly exposed to water which, if renewed regularly by flow, would eventually have a pH close to that of the environment.
Huang, Weiji (ExxonMobil Development Company) | Lafontaine, John (ExxonMobil Development Company) | Cao, Fang (ExxonMobil Research and Engineering) | Hornemann, Jennifer (ExxonMobil Upstream Research Company)