James H. Russell

Corrosion and Polarization Behavior of Sensitized High-Nitrogen Stainless Steels

Abstract Corrosion of a sensitized high-nitrogen stainless steel (SS, nominally Fe-19% Cr-5% Ni-5% Mn-3% Mo-0.024% C-0.69% N) was studied by examining potentiodynamic polarization curves. Corrosion behavior was compared to previously reported sensitization values. The SS was heat treated at temperatures of 600°C to 1,000°C for times up to 1,000 h. Potentiodynamic polarization curves were generated in deaerated 1 N sulfuric acid (H2SO4) + 0.01 M potassium thiocyanate (KSCN) at 30°C at a scan rate of 100 mV/min. Corrosion currents measured at the corrosion potential did not change in the same manner with increasing aging time as values for the degree of sensitization (DOS). This was believed to be caused by greater sensitivity to chromium depletion during potentiodynamic polarization testing compared to sensitization measured by electrochemical potentiokinetic reactivation (EPR) testing (i.e., the minimum chromium level in the depletion zone required to cause sensitization, ≈14 wt%, was lower than that requ...

PERFORMANCE OF ZINC ANODES FOR CATHODIC PROTECTION OF REINFORCED CONCRETE BRIDGES

Operation of thermal spray zinc (Zn) anodes for cathodic protection (CP) of reinforced concrete structures was investigated in laboratory and field studies conducted by the Albany Research Center (ARC) in collaboration with the Oregon Department of Transportation. The purposes of the research presented in this report were: evaluate the need for preheating concrete to improve the adhesion of the anode; estimate the service life of thermal spray Zn CP anodes; determine the optimum thickness for Zn CP anodes; characterize the anode-concrete interfacial chemistry; and correlate field and laboratory results. Laboratory studies involved accelerated electrochemical aging of thermal sprayed Zn anodes on concrete slabs, some of which were periodically wetted while others were unwetted. Concrete used in the slabs contained either 1.2 or 3 kg NaCl /m3 (2 or 5 lbs NaCl /yd3) as part of the concrete mix design. The Zn anodes were applied to the slabs using the twin wire arc-spray technique. Half of the slabs were preheated to 120-160 C (250-320 F) to improve the initial Zn anode bond strength and the other half were not. Accelerated aging was done at a current density of 0.032 A/m2 (3 mA/ft2), 15 times that used on Oregon DOT Coastal bridges, i.e, . 0.0022 A/m2 (0.2 mA/ft2) Cores from the Cape Creek Bridge (OR), the Richmond San Rafael Bridge (CA), and the East Camino Underpass (CA) were used to study the anode-concrete interfacial chemistry, to relate the chemistry to electrochemical age at the time of sampling, and to compare the chemistry of the field anodes to the chemistry of anodes from the laboratory studies. Cores from a CALTRANS study of a silane sealant used prior to the application of the Zn anodes and cores with galvanized rebar from the Longbird Bridge (Bermuda) were also studied. Aged laboratory and field anodes were characterized by measuring some or all of the following parameters: thickness, bond strength, anode-concrete interfacial chemistry, bulk chemistry, anode resistance, circuit resistance, electrochemical age, and air and water permeability. Models are presented for the operation of periodically-wetted and unwetted thermal spray Zn anodes from the initial energizing of the anode to the end of its service life. The models were developed in terms of bond strength, circuit resistance, anode-concrete interfacial chemistry, electrochemical age, and anode condition. The most significant results of the research are: (1) preheating concrete surfaces prior to coating with Zn is unnecessary; (2) anodes generally fail due to loss of bond strength rather than Zn consumption; (3) Unwetted anodes fail more quickly than periodically-wetted anodes; (4) 0.47-0.60 mm (12-15 mil) anode thickness is adequate for most Oregon DOT coastal impressed current CP (ICCP) installations; (5) based on bond strength, thermal spray Zn ICCP anode service life is approximately 27 years at 0.0022 A/m2 (0.2 mA/ft2); (6) anode reaction products alter the anode-concrete interface by rejecting Ca from the cement paste, by replacing it with Zn, and by the accumulation of a Zn mineral layer that includes chloride and sulfur compounds; (7) CP system circuit resistance provides an effective means for monitoring the condition of Zn ICCP anodes as they age.

Applications of electrochemical methods for investigations of localized corrosion of nitrogen-molybdenum stainless steels

Electrochemical methods were used to determine the localized corrosion resistance of 12 austenitic stainless steels (SS) with a composition range of 22%Cr-5%Ni-5%Mn-(1% to 5%)Mo-(0.0% to 0.7%)N-balance Fe in a deaerated 3.5 wt% sodium chloride (NaCl) solution from 10°C to 97°C. Potentiodynamic polarization was used to determine the critical pitting potential (CPP), protection potentials, and polarization resistance (Rp), and potentiostatic cyclic thermometry was used to determine the critical pitting temperature (CPT) and critical crevice temperature (CCT). The results of potentiodynamic polarization showed that all of the SS containing both N and Mo have CPP significantly higher than either Type 304 (UNS S30400) or Type 316L (UNS S31603) SS. Rp correlated with the pitting resistance equivalent (PRE) for PRE from 20 to 45; however, for PRE > 45 there was no correlation. Results obtained by potentiostatic cyclic thermometry showed that CPT and the CCT are both linear functions of PRE, and strongly dependent on both Mo and N concentration in the alloy.

Humectant Use in the Cathodic Protection of Reinforced Concrete

Abstract Use of humectants to improve the thermal-sprayed zinc anode performance during the cathodic protection (CP) of reinforced concrete was examined. A humectant is a hygroscopic material. It i...

Humectants To Augment Current From Metallized Zinc Cathodic Protection Systems on Concrete

Cathodic protection (CP) systems using thermal-sprayed zinc anodes are employed to mitigate the corrosion process in reinforced concrete structures. However, the performance of the anodes is improved by moisture at the anode-concrete interface. Research was conducted to investigate the effect of hydrophilic chemical additives, humectants, on the electrical performance and service life of zinc anodes. Lithium bromide and lithium nitrate were identified as feasible humectants with lithium bromide performing better under galvanic CP and lithium nitrate performing better under impressed current CP. Both humectants improved the electrical operating characteristics of the anode and increased the service life by up to three years.

Electrochemical Noise Sensors for Detection of Localized and General Corrosion of Natural Gas Transmission Pipelines. Final Report for the Period July 2001-October 2002

The U.S. Department of Energy, National Energy Technology Laboratory funded a Natural Gas Infrastructure Reliability program directed at increasing and enhancing research and development activities in topics such as remote leak detection, pipe inspection, and repair technologies and materials. The Albany Research Center (ARC), U.S. Department of Energy was funded to study the use of electrochemical noise sensors for detection of localized and general corrosion of natural gas transmission pipelines. As part of this, ARC entered into a collaborative effort with the corrosion sensor industry to demonstrate the capabilities of commercially available remote corrosion sensors for use with the Nations Gas Transmission Pipeline Infrastructure needs. The goal of the research was to develop an emerging corrosion sensor technology into a monitor for the type and degree of corrosion occurring at key locations in gas transmission pipelines.