Seawater systems materials

In this connection one should be aware of the possibility to protect critical parts of a system (equipment, plant) by means of less noble and less critical structural components in the same system, i.e. the corrosion is localized to preferred parts of the system. For instance, stainless steel pipes, fittings, pumps and valves in seawater systems can be protected against serious deterioration by use of pipe sections of unalloyed steel or cast iron. These sections must be easy to replace, or they must have relatively large wall thickness and/or large exposed surface area in relation to the more noble materials. In heat exchangers, relatively thick tube plates of steel can be used in combination with tubes of a copper alloy. 

The use of stainless steel in oil production has increased, and is of particular significance for production in deep waters. This applies both to production and process equipment carrying oil and gas and to seawater systems. For seawater systems the experience from nuclear power plants has been useful. In these plants, some high-alloy steels have performed well in equipments such as seawater pumps and heat exchangers. But the performance depends on service conditions, design and combination of materials. On the oil/gas side, good experience has been obtained with 13% Cr steel in production tubing, in components at the wellhead and in well valves. The same can be said about the use of other stainless steels in process systems offshore, but there have been some exceptions. For instance, SCC has occurred on duplex steel (22-5-3) under external heat insulation (compare Section 7.12) [10.11]. 

A flow-system utilizing a miniature column packed with SG-8HOQ was used for the preconcentration of Cd, Pb, Zn, Cu, Fe, Mn, Ni, and Co from seawater prior to their determination by GFAAS. A preconcentration factor sufficient to permit the analysis of an open seawater reference material, using a 50 ml sample, was obtained. Recoveries of the above elements from seawater averaged 93% (range 87-97%) with absolute blanks ranging between 0.04 ng (Ni) and 4.0 ng (Fe). " ... 

Strandmyr, O. and Hagemp, O., Field Experience with Stainless Steel Materials in Seawater Systems, Corrosion/98, Paper 707, Houston, TX NACE International, 1998. 

This subject is dealt with more thoroughly in "Materials and Treatments for Seawater Systems", 420 pages, soon to be published by Editions Technip. 

Materials and Treatments for Seawater Systems, Comics des Techniciens,... 

Such a system would automatically and quickly give information as to whether a sample had been exposed to seawater, ionic materials or even possibly blood serum. Multifunctional detection is relatively new and holds exciting possibilities for future use. It is likely that we can look forward further... 

Seawater systems are used by many industries, such as shipping, offshore oil and gas production, power plants, and coastal industrial plants. The main use of seawater is for cooling purposes, but it is also used for firefighting, oilfield water injection, and desalination plants. The corrosion problems in these systems have been well-studied over many decades, but despite published information on materials behavior in seawater, failures still occur. 

A third auxiliary effect is the deposition of compounds from the soil on the buried system. This effect is extremely pronounced in seawater, where a cathode scale resembling hard glossy enamel can build up over time and grow as thick as 2 cm. When deposited in seawater, this material is a complex mixture of calcium and magnesium oxides, hydroxides, and carbonates. The composition of this hard deposit depends upon CP current density, among other factors (see Chap. 8 for details on calcareous deposits). 

The first successful major use of stainless steel for seawater systems was in the Gullfaks oilfield in the Norwegian offshore sector where Avesta 254SMO (21% Cr, 18% Ni, 6% Mo, 0.2% N) was adopted. The reason for this selection was the need for a material resistant to alternate exposure to seawater and sulfide-containing oil in the storage/ballast spaces in concrete platforms. Several thousand tonnes of superaustenitic stainless steel are now in service, mainly on offshore platforms. ... 

Todd, B., Materials Selection for High Reliability Seawater Systems, http //marine.copper.org /, 1998. 

Although numerous mud additives aid in obtaining the desired drilling fluid properties, water-based muds have three basic components water, reactive soHds, and inert soHds. The water forming the continuous phase may be fresh water, seawater, or salt water. The reactive soHds are composed of commercial clays, incorporated hydratable clays and shales from drilled formations, and polymeric materials, which may be suspended or dissolved in the water phase. SoHds, such as barite and hematite, are chemically inactive in most mud systems. Oil and synthetic muds contain, in addition, an organic Hquid as the continuous phase plus water as the discontinuous phase. 

Saline Water for Municipal Distribution. Only a very small amount of potable water is actually taken by people or animals internally, and it is quite uneconomical to desalinate all municipally piped water, although all distributed water must be clear and free of harmful bacteria. Most of the water piped to cities and industry is used for Htfle more than to carry off small amounts of waste materials or waste heat. In many locations, seawater can be used for most of this service. If chlorination is requited, it can be accompHshed by direct electrolysis of the dissolved salt (21). Arrayed against the obvious advantage of economy, there are several disadvantages use of seawater requites different detergents sewage treatment plants must be modified the usual metal pipes, pumps, condensers, coolers, meters, and other equipment corrode more readily chlorination could cause environmental poUution and dual water systems must be built and maintained. 

Galvanic or impressed current anodes are used to protect these components. The anode material is determined by the electrolyte zinc and aluminum for seawater, magnesium for freshwater circuits. Platinized titanium is used for the anode material in impressed current protection. Potential-regulating systems working independently of each other should be used for the inlet and outlet feeds of heat exchangers on account of the different temperature behavior. The protection current densities depend on the material and the medium. 

Since the formation nature and breakdown of protective surface films depends on both material and environmental parameters such influences on erosion corrosion will be discussed together. Particular attention will be paid to the copper/seawater and carbon steel/water (steam) systems. 

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