Tommaso Pastore

Cathodic protection and cathodic prevention in concrete: principles and applications*

The paper deals with the principles of cathodic protection for atmospherically exposed concrete structures, the various protecting effects induced by the cathodic polarization and tests and field experience results. The differences between the cathodic protection applied for controlling the corrosion rate of chloride contaminated co nstructions and that applied to improve the corrosion resistance of the reinforcement of new structures expected to become contaminated are then underlined and discussed. The more recent applications of cathodic protection on carbonated concrete are also illustrated. The operating conditions (voltage and current applied), the throwing power, the protection conditions which avoid the risk of hydrogen embrittlement in prestressed structures are also discussed. Examples of cathodic protection and of cathodic prevention are also presented.

Cathodic protection of new and old reinforced concrete structures

Current and potential distributions measured on concrete slabs and simulated by computer modelling are discussed in relation with the application of cathodic protection to new reinforced structures as a corrosion preventive method. The results show high penetration of cathodic protection over the depth of uncontaminated concrete, so that even a rebar relatively distant from the anode can be polarized, whereas the penetration is limited to the rebars near to the anode in chloride contaminated slabs with corroding rebars. The great throwing power and the wide range of protection potentials for uncorroding concrete structure enable safe application of the cathodic protection even to new prestressed structures.

Behaviour of Stainless Steel in Simulated Concrete Pore Solution

AbstractThe localised corrosion behaviour of austenitic, martensitic, and duplex stainless steels has been studied in several solutions simulating the liquid present in the pores of both alkaline and carbonated concrete in the presence of chloride ions. The work aimed to evaluate the suitability of these types of stainless steel as rebars in reinforced concrete structures exposed to very aggressive environments. Electrochemical tests have been performed in solutions with pH values in the range 7·6-13·9, chloride concentration in the range 0-10%, and temperatures of 20 and 40°C. The adverse effect of a decrese in pH on the critical chloride content is discussed, as a function of stainless steel composition and temperature, and the inhibitive effect of high carbonate/bicarbonate concentrations is also shown.

Steel Corrosion Monitoring in Normal and Total-lightweight Concretes Exposed to Chloride and Sulphate Solutions. Part I: Potential Measurements

The paper reports on long time testing of reinforcement corrosion in normal and total-lightweight concretes exposed to cycles consisting of 4 phases: chloride salt fog, drying, sulphate solution immersion, drying. Potential monitoring evidenced a passive condition for all reinforcements embedded in normalweight concretes. The initiation of the corrosive attack in total-lightweight concretes could not be evidenced, although low potential values were found on corroding reinforcements.

Application of the Boundary‐Element Method to Offshore Cathodic Protection Modeling

This paper deals with the main aspects of the calculation of current and potential distributions and summarizes some results obtained on different systems using a computer program based on the boundary-element method. Model results are compared to literature data for well-known geometries, and to experimental data obtained both in laboratory testing with a suitable cell and infield testing on offshore structures (in particular platform nodes). The good predictive capability of computer modeling is shown.

The sulfide stress corrosion cracking of high alloy stainless steels for oil and natural gas wells

The stress corrosion cracking resistance of some martensitic, precipitation hardening, duplex and high alloy austenitic stainless steels for oil or gas wells has been investigated. Different test methods have been utilized: constant load tests on smooth specimens with and without crevices, constant deformation tests on precracked specimens, and constant elongation rate tests on smooth specimens. The tests have been carried out in a NACE environment and in a modified NACE environment. The tests confirmed both the susceptibility to stress corrosion cracking of the martensitic and the precipitation hardening stainless steels and the resistance of the high austenitic stainless steel. Some tests showed the stress corrosion cracking susceptibility of the duplex stainless steel to be worse than expected from traditional tests.

Steel corrosion monitoring in normal and total-lightweight concretes exposed to chloride and sulphate solutions part II: Polarisation resistance measurements

The paper reports on long time testing of reinforcement corrosion in high strength normal and total-lightweight concretes exposed to cycles consisting of 4 phases: chloride salt fog, drying, sulphate solution immersion, drying. Polarisation resistance monitoring performed for evaluating corrosion rates confirmed passive condition for all reinforcements embedded in normalweight concretes. The initiation of the corrosive attack was detected in all the reinforcements in total-lightweight concretes. Corrosion rates up to 400 μm/year were detected.

Macrocell effects on potential measurements in concrete cathodic protection systems

Abstract The electrochemical situation that arises in reinforced concrete structures equipped with a cathodic protection (CP) anode when CP is not energized was studied. A macrocell effect between anode and cathode was shown to arise even in the absence of a direct connection, inducing alterations in potential measurements. In chloride (Cl−)-contaminated structures where CP was not energized, the presence of the anodic system enhanced localized corrosion. In structures where CP was in operation, potential monitoring, namely of instant-off potential and 4-h decay, was affected.

Evaluation of the resistance to hydrogen embrittlement by the slow bending test

Publisher Summary This chapter investigates a slow strain rate (SSR) bending technique employed for studying the resistance of steels to hydrogen embrittlement under cathodic protection. Four steels having tempered martensitic microstructures and tensile yield strengths ranging from 497–770 MPa were tested. Tests were carried out in an aerated 3.5% NaCI solution with a recirculation system. Slow bending tests were carried out with 10 × 25 × 230 mm specimens having 180 mm span length by using a hydraulic tensile machine assisted by a computer. Roller pins of 20 mm diameter were used. The surfaces of specimens were coated by epoxy resin in order to minimize cathodic protection current. Microcracks were observed in the necking zone of specimens with little brittle areas of crack growth; they had 45°-orientation on the lateral surface. Further increases of applied potentials resulted in the totally ductile behavior of steels, similar to that found when steels were tested in air. The susceptibility of steels to hydrogen embrittlement, inducing the appearance of secondary cracks and brittle crack propagation, was related to the critical values of applied cathodic potentials.

Corrosion Behavior of Heat-Treated AlSi10Mg Manufactured by Laser Powder Bed Fusion

This experimental work is aimed at studying the effect of microstructural modifications induced by post-processing heat treatments on the corrosion behavior of silicon-aluminum alloys produced by means of laser powder bed fusion (LPBF). The manufacturing technique leads to microstructures characterized by the presence of melt pools, which are quite different compared to casting alloys. In this study, the behavior of an AlSi10Mg alloy was evaluated by means of intergranular corrosion tests according to ISO 11846 standard on heat-treated samples ranging from 200 to 500 °C as well as on untreated samples. We found that temperatures above 200 °C reduced microhardness of the alloy, and different corrosion morphologies occurred due to the modification of both size and distribution of silicon precipitates. Selective penetrating attacks occurred at melt pool borders. The intergranular corrosion phenomena were less intense for as-produced specimens without heat treatments compared to the heat-treated specimens at 200 and 300 °C. General corrosion morphologies were noticed for specimens heat treated at temperatures exceeding 400 °C.