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Wax, hydrates, and asphaltenes are the three major threats to flow assurance that must be assessed by design teams. These potential problems can dramatically change system selection and operational procedures. If one of them is discovered after the system is under construction or worse after first oil then the whole project may be at risk. Each solid must be well understood by engineers so they can neutralize the threats to system uptime that result from poor solids management. This paper focuses on the problems posed by, and the system implications of, wax, hydrates, and asphaltenes.

A model is presented for corrosion of carbon steel in 60-96% weight sulfuric acid with correlations and data to facilitate quantitative use of the model for mechanical and process design. Corrosion is limited by the rate of convective mass transfer of ferrous ion from a ferrous sulfate (corrosion product) film-liquid interface into bulk acid. This interface is saturated with ferrous ion. The model has been verified in both laboratory and plant acids with rotating cylinder and pipeline geometries and with a variety of carbon and low alloy steels. Ferrous ion is an inhibitor for corrosion, and sacrificial corrosion in certain equipment in plants in which acid is recirculated can protect other critical items in the system. Changing liquid levels in storage tanks, acid purges, addition of iron, and lining of vessels can affect corrosion rate in a plant system.Sulfuric acid is an industrial catalyst for numerous organic chemical reactions, such as hydrations and alkylations, to produce many important commodities, such as alcohols, ethers, and gasoline. It is desirable to design plants so that carbon steel can be utilized in preference to more expensive materials as much as possible. Toward this end, quantitative corrosion models valid under chemical and fluid flow conditions anticipated for the plant are most useful. These conditions include presence of various chemical reactants in the acid as well as corrosion products which build up in the system because acid is continuously separated from desired chemical products and recirculated.Much has been written about the corrosion of steel in concentrated sulfuric acid (1). An overview of the corrosion system can be gained by measuring the density of current supplied to a vertical rectangular specimen of AISI !020 steel in stirred 70% weight acid in order to maintain the electrochemical potential of the specimen fixed (see Fig. 1). Two distinct regions appear in the anodic portion of this current potential curve. One is the "sulfation" range (--0.3 to +0.3V with respect to Ag/AgC1 1M CI) where the current is independent of potential. Hines and Williamson found the film formed in this range to be duplex, the inside layer being a thin compact film and the outside layer a thick porous ferrous sulfate film (2). At 50 mV negative to the corrosion potential (here about --0.4V), the anodic rate measured by weight loss is identical to this rate in the sulfation region. The independence of anodic current density on potential near (both positive and negative) the corrosion potential implies that the anodic current, in the sulfation range, is also equal to the free corrosion rate. That is, the anodic process limits the corrosion rate.The second distinct region appearing in the current potential diagram is the passive range, greater than +0.5V, where the steel is apparently covered by a ferric sulfate film over a passive oxide film (3, 4). The sharp peak at about +0.5V in Fig. 1 results from the change in oxidation states of the iron sulfate film already existing on the metal surface....

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