Erosion-corrosion locations

Favored locations for erosion-corrosion are areas exposed to high-flow velocities or turbulence. Tees, bends, elbows (Fig. 11.5), pumps, valves (Fig. 11.6), and inlet and outlet tube ends of heat exchangers (Fig. 11.7) can be affected. Turbulence may be created downstream of crevices, ledges (Fig. 11.8), abrupt cross-section changes, deposits, corrosion products, and other obstructions that change laminar flow to turbulent flow. 

Erosion/corrosion of the weld bead at the fracture location damaged the aluminum oxide film on the piping, thus allowing the mercury to wet and initiate cracking of the aluminium. 

Figure 15.7 (a, c) Secondary electron images of erosion-corrosion surfaces (b, d) Corresponding location (white line) of the focused ion beam (FIB) cross-sections. Reprinted from Ref. [13], Copyright (2007) with permission from Elsevier. 

Structure foundation needs to be located and designed such that environmental and geologic factors or conditions, including frost, scorn, erosion, corrosion, seepage, piping of foundation soils, or future planned and anticipated developments and other human actives will not jeopardize its stability as well as functionality during the design life. 

Erosion-corrosion is encountered most frequently in pumps, valves, centrifuges, elbows, impellers, inlet ends of heat-exchanger tubes, and agitated tanks. Locations in flowing systems where there are sudden changes in direction or flow cross-section, as in heat exchangers where water flows from the water boxes into the tubes, are likely places for erosion-corrosion. 

The case-study is based on an actual sand erosion issue present in an offshore oil production system. Material degradation due to processes of erosion/corrosion is the main focus. The production system is located subsea and connected to a spread-moored FPSO (Floating Production Storage and Offloading) unit, which is used as a hub, processing the fluids produced from the subsea wells. 

Cavitation damage is a fairly common form of erosion-corrosion of pumps, impellers or hydrauhc turbine internals. Cavitation is caused by collapsing gas bubbles at high-pressure locations adjacent metal surfaces are damaged by the resultant hydraulic shock waves. Cavitation damage is usually in the form of loosely spaced pits that produce a roughened surface area. 

Basic to establishing whether power recovery is even feasible, let alone economical, are considerations of the flowing-fluid capacity available, the differential pressure available for the power recovery, and corrosive or erosive properties of the fluid stream. A further important consideration in feasibihty and economics is the probable physical location, with respect to each other, of fluid source, power-production point, and final fluid destination. In general, the tendency has been to locate the power-recoveiy driver and its driven unit where dictated by the driven-unit requirement and pipe the power-recoveiy fluid to and away from the driver. While early installations were in noncorrosive, nonerosive services such as rich-hydrocarbon absorption oil, the trend has been to put units into mildly severe seiwices such as amine plants, hot-carbonate units, and hydrocracker letdown. 

Process locations containing large volumes or high pressure hydrocarbon gases which might be susceptible to extreme effects of erosion or corrosion from the process activity. 

Although the committee found that continuous SCWO would effectively mineaalize agent neutralents, it concluded that issues related to the mechanisms and locations of salt buildnp, the chemical composition of the salts produced, and the effectiveness of the flushing of salts are unresolved. Corrosion and plugging of SCWO reactors, erosion of valve seats and nozzles, and pressure containment are other issues to be addressed. As a result, the committee ranked continu-ons SCWO fairly low as a process for mineralizing MMD nentralents. 

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