SCIENCEspond to changes in both pH and chromate ion activity. Relative locations of the electrodes in the cell may have contributed. Ag-15-R was in front of Ag-16-R for Experiment 1 and exhibited higher voltages and more dramatic responses. Ag-14-R later developed unusually high potentials in this same location. The electrode housings were in electrical contact with the autoclave, and corrosion currents cause iR offset voltages when they flow past both the test electrode and the Pt reference. Local heating probably did not contribute, but examining this possibility directly is difficult.Interpretation of these results is neither easy nor unambiguous. Takagi et al. 8 measured the effect of y radiation on the corrosion potential of type 304 SS and reported a positive shift in NWC, negative in HWC. However, there was general consistency among the results of the present experiments, and it appears that:Pt electrodes with a brazed pressure seal operate well in HWC, but can develop a mixed corrosion potential without excess H 2 .Fe/Fe3O4 seemed more stable and may be preferable to Cu/Cu 20 for the reference couple of pH electrodes in a radiation field.Polymer-free Ag/AgCI electrodes are suitable for use in highintensity ionizing radiation, but may require a simple calibration to provide the theoretical reference potential. Transient decreases to stable values that depend on the dose rate probably stem from water radiolysis in the reference chamber. The electrode potential may return to the theoretical value when the reference chamber approaches a true steady-state concentration of chemical species. ABSTRACTA consequence of corrosion of steel in the presence of oxygenfree carbon dioxide and a water phase is the formation of an iron carbonate (FeCO 3) corrosion scale. This scale provides some protection of the steel from further corrosion. The protectiveness of the scale depends on environmental factors and characteristics of the steel. Information presented here describes structural characteristics of iron carbonate scales and discusses how structure may affect the corrosion mechanism. Examinations of iron carbonate scales revealed two kinds of scales and variations in scale thickness depending on the steel microstructure.

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A semi-empirical procedure has been developed for predicting erosion rates in pipe geometries, such as elbows and tees. The procedure can be used to estimate safe operating conditions and velocities in oil and gas production where sand is present. In the proposed procedure, a concept is introduced that allows determination of erosion rate for different pipe geometries. In the procedure, based on empirical observations, the erosion rate is related to the impact velocity of sand particles on a pipe fitting wall. A simplified particle tracking model is developed and is used to estimate the impact velocity of sand particles moving in a stagnation region near the pipe wall. A new concept of equivalent stagnation length allows the simplified procedure to be applicable to actual pipe geometries. The “equivalent stagnation regions” of an elbow and a tee geometry of different sizes are obtained from experimental data for small pipe diameters, and a computational model is used to extend the procedure to larger pipe diameters. Currently, the prediction method applies to mild steel and accounts for the effects of sand size, shape, and density; fluid density, viscosity, and flow speed; and pipe size and shape. The proposed method has been verified for gas and liquid flows through several comparisons with experimental data reported in the literature. The results of the model accurately predict the effects of sand size and fluid viscosity observed in the experiments. Furthermore, predicted erosion rates showed good agreement with experimental data for gas, liquid, and gas-liquid flows in several 50.8-mm (2-in.) elbows and tees.

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The commonly used practice for controlling sand erosion in gas and oil producing wells is to limit production velocities following the API RP 14E. This guideline contains a procedure to calculate a threshold velocity, the flow velocity below which an allowable amount of erosion occurs. While providing advantages of computational ease, the approach has some disadvantages. One is that, while many factors influence the erosion rate, RP 14E includes only one factor, the density of the medium. Thus, factors such as flow geometry, type of metal, sand size, and Reynolds number are not accounted for. Another disadvantage is that the tolerable amount of erosion, in terms of loss of wall thickness, is not specified in RP 14E. A method is presented to overcome these disadvantages by (1) accounting for many of the physical variables in the flow and erosion processes and (2) including a way to predict the maximum penetration rate for sand erosion. The capabilities of the method are evaluated by comparing predicted penetration rates with experimental data found in the literature. In this paper, the method is applied to calculate threshold velocities. The computational procedure allows an allowable amount of erosion to be specified in mils per year for elbows, tees and direct impingement geometries. Threshold flowstream velocities are calculated for carrier fluids of crude oil, water, and methane at elevated pressure. Resulting threshold velocities are presented for a range of sand sizes, pipe diameters, sand production rates, and methane pressures. Results show that threshold velocities for single phase gas flows are much lower than threshold velocities for single phase liquid flows. Introduction Sand erosion is a major problem in many production situations because small amounts of sand entrained in the produced fluid can result in significant erosion and erosion/corrosion damage. Even in "sand free" or clean service situations where sand production rate is as low as a few pounds per day, erosion damage could be very severe at high production velocities. Sand erosion can also cause localized erosion damage to protective corrosion scales on pipe walls and result in accelerated erosion/corrosion damage. The objective of this work is to develop guidelines for predicting a threshold velocity and/or particle size below which only a small, allowable amount of erosion occurs. Threshold velocity guidelines help operators to estimate safe production velocities in erosive services, and serve as a tool to engineers for the cost effective design of piping systems, the selection of piping materials, and the selection of appropriate screen sizes for new wells.