Case, Raymundo (ConocoPhillips) | Rincon, Hernan (ConocoPhillips) | Tang, Xuanping (Institute for Corrosion and Multiphase Technology, Department of Chemical and Biomolecular Engineering, Ohio University)
Corrosion resistance alloys (CRAs) used in oil and gas industry may suffer severe localized corrosion such as pitting and crevice corrosion. Critical pitting temperatures (CPT) determined by ASTM G48-03 and ASTM G150-99 standard procedures are suitable for ranking the susceptibility of stainless steel to pitting corrosion but not appropriate for predicting pitting corrosion of stainless steel under production conditions. Some researchers have proposed the use of electrochemical noise (ECN) to estimate values of CPT on stainless steel. However the criteria used to determine these values are not consistent among them. A methodology based on electrochemical testing techniques was implemented to measure the CPT of SS 316L in 1 M, 2M sodium chloride and 6% ferric chloride solutions in a temperature range of 0-80°C. Results suggest that the interpretation of electrochemical noise data may result in a false CPT. The use of a combination of electrochemical noise, cyclic potentiodynamic polarization and potentiostatic technique can be used to determine the correct CPT for stable pitting. High temperature tests in autoclaves simulating production conditions in the future are recommended for the verification of this methodology.
It is generally accepted that susceptibility of stainless steels to pitting corrosion increases with temperature. Pitting corrosion of stainless steels can be characterized by the critical pitting temperature (CPT), which is defined as the lowest temperature at which stable pitting is possible.1 This temperature limit is defined as potential independent CPT. The measurements of CPT have been of greatest practical interest for many researchers since CPT is typically used as a tool for ranking the resistance of stainless steel to pitting corrosion. Many different techniques have been developed and used for CPT measurements, which can be classified into four categories, traditional immersion test, potentiodynamic technique, potentiostatic technique and electrochemical noise (ECN) technique.
Huang, Weiji (ExxonMobil Development Company) | Lafontaine, John (ExxonMobil Development Company) | Cao, Fang (ExxonMobil Research and Engineering) | Hornemann, Jennifer (ExxonMobil Upstream Research Company)
ABSTRACT The effects of limited remote cathode area on crevice corrosion propagation, repassivation and reorganization were investigated on 316 stainless steel (UNS S31600) in 0.6 M NaCl at 50˚C. Both multiple crevice assemblies (MCA) and rescaled crevices enabling testing of coupled multi-electrode arrays (CMEA) were utilized. Potentiostatically activated crevices were subjected to situations which limited propagation by either (i) stepping the potential from levels required to initiate crevice corrosion to those below the repassivation potential, (ii) performing a downward or negative scan of the potential from high potential, or (iii) progressively decreasing the area of a galvanically coupled platinum cathode situated outside the crevice after periods of crevice corrosion propagation. In the first two cases, repassivation occurred when the potential reached the lower statistical limit of the repassivation potential measured on creviced specimens in a downward scan. During the galvanically coupled test, repassivation occurred when the galvanic cathodic current supplied became lower than the current required to maintain a couple potential equal to the repassivation potential at the mouth of the crevice. Thecrevice anode sites simultaneously reorganized into smaller active areas active deeper in the crevice. Application of Galvele’s product for crevice stabilization suggested that such low potentials lowered the chemical stability product i·a or i·(a+d) where d is the crevice depth and a is the depth of crevice corrosion at individual crevice sites below a critical level. INTRODUCTION One of the earliest stages of crevice corrosion initiation requires the separation of the anode and the cathode, as described by Oldfield and Sutton.1 This occurs after the oxygen present in the crevice is completely depleted by the local cathodic reactions where the rate of cathodic reactions exceeds the transport rate of oxygen into crevices. The major cathode is then repositioned to the oxygen rich environment outside the crevice and will support the anodic reactions in the crevice.
Chiang, Kuang-Tsan Kenneth (Department of Earth, Material, and Planetary Sciences Geosciences and Engineering Division Southwest Research Institute) | Yang, Lietai (Department of Earth, Material, and Planetary Sciences Geosciences and Engineering Division Southwest Research Institute)
ABSTRACT Corrosion of buried, ferrous-based metallic piping is a significant and ongoing expense on Army and DoD installations for sewer/industrial waste lines, potable water distribution lines, heat distribution piping and other assorted piping. The focus of this study is to evaluate the use of cementitious material, flowable backfills known as Controlled Low Strength Materials (CLSM), to completely encase buried steel pipes. The highly alkaline environment is known to create a passivated, corrosion-mitigating layer on the surface of the steel. Experiments have been set up to evaluate the corrosion mitigation effects of mixtures of flowable fill and soil-cement. The flowable backfills were studied with and without cathodic protection. A field evaluation at Fort Hood, TX has been operating concurrently with a lab evaluation held at U.S. Army ERDC-CERL. The results are not yet complete, and will be available in a future manuscript, but the expectation is for a significantly decreased corrosion rate with flowable backfills in conjunction with cathodic protection. INTRODUCTION A common approach to corrosion protection at several Army installations is via material choice and the extensive use of cathodic protection. In many cases a non-metallic piping material will not be sufficient for long term, reliable service. In the case of cathodic protection, an ongoing maintenance and monitoring program is required. This involves the employment and periodic training for a number of inspectors as well as the ongoing inspections themselves. Additionally, whenever a problem is detected, corrective action is immediately required to prevent the advance of corrosive degradation on buried piping. If instead the local pH at the surface of the pipe were to be manipulated to be extremely high, then the corrosion rate could be sharply reduced or even stopped. Such an effect can be achieved through the use of an alkaline cementitious material typically called "flowable backfill."
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.
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.