Pipework reactions

Experience indicates that a special word of warning is needed on the subject of pipework reactions for two-phase (or three-phase) flow when one of the phases is gas. It is possible to estimate theoretically the reaction on the pipe supports at a bend when a slug of solid or liquid of given size traverses the bend, or alternatively a vapour bubble (a negative mass of displaced liquid) traverses the bends. 

Consider for instance a slug of solids of mean density p (= 500) kg/m and length / m, travelling at V (- 20) m/s in a pipe of diameter d (= 0.2) m, traversing a 90° bend which has a radius of 1.5 /. One can make a rough estimate of the reaction on the pipe by postulating that 

Change of momentum = mass x velocity change = —dHpV 

Time taken for change = distance traversed/speed = — M)IV Dividing and simplifying 

This will clearly not hold for I length of the bend — d), so if we take 

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The electrolysis protection process using impressed current aluminum anodes allows uncoated and hot-dipped galvanized ferrous materials in domestic installations to be protected from corrosion. If impressed current aluminum anodes are installed in water tanks, the pipework is protected by the formation of a film without affecting the potability of the water. With domestic galvanized steel pipes, a marked retardation of the cathodic partial reaction occurs [15]. Electrolytic treatment alters the electrolytic characteristics of the water, as well as internal cathodic protection of the tank and its inserts (e.g., heating elements). The pipe protection relies on colloidal chemical processes and is applied only to new installations and not to old ones already attacked by corrosion. 

The metal lost from the inside of pumps, reaction vessels, pipework, etc. usually contaminates the product. The implications of this depend upon the product. Ppb levels of iron can discolor white plastics, though at this level the effect is purely cosmetic. Ppm levels of iron and other metals affect the taste of beer. Products sold to compositional requirements (such as reagent-grade acids) can be spoiled by metal pick-up. Pharmaceutical products for human use are often white tablets or powders and are easily discolored by slight contamination by corrosion products. 

Important applications for titanium have been developed in processes involving acetic acid, malic acid, amines, urea, terephthalic acid, vinyl acetate, and ethylene dichloride. Some of these represent large scale use of the material in the form of pipework, heat exchangers, pumps, valves, and vessels of solid, loose lined, or explosion clad construction. In many of these the requirement for titanium is because of corrosion problems arising from the organic chemicals in the process, the use of seawater or polluted cooling waters, or from complex aggressive catalysts in the reaction. 

Some industries, notably the fine chemicals and parts of the food processing industry, cannot tolerate the pick-up of even small quantities of metal ions in their products. To avoid corrosion, plants often have to incorporate lined pipework and reaction vessels, while in a slightly less demanding situation whole plants are made of an appropriate grade of stainless steel. The capital investment in these industries is thus considerably increased due to the necessity to avoid corrosion. 

Depending on the degree of oxygen infiltration, the temperature of the condensate and the presence of other gases such as carbon dioxide, various corrosion reactions may take place in the steam distribution and CR systems. The most basic reaction associated with oxygen infiltration results in oxygen corrosion, which can produce deep pitting in the pipework and is described later in this chapter. 

The initial reaction with the steel condensate pipework is ... 

In the induced jarosite precipitation and primary neutralization processes, this is typically done in-slurry, at temperatures in excess of 80°C. Few issues with scale formation occur, apparently due to the presence of a large surface area available from the leach residue solids, relative to equipment surfaces. It is important to provide adequate retention time for the complete reaction of the limestone, to avoid reactions continuing to occur in downstream thickeners and pipework. Such reactions can lead to both process upsets and scale formation over the longer term. 

For this paper, a few technical interventions in that reaction section are calculated. The interventions represent alterations in the assembly or operation of the unit. The interventions are presented as changes to the base-case calculation. That is to say the calculation that only incorporates unaltered equipment LoC models. The results for the base-case are presented section 4.1. The interventions are treated in the subsequent sections. Section 4.2 treats changes of the PRVs (Pressure Relief Valves) in the unit. That is to say, SIL 3 PRVs are replaced by SIL 4 PRVs. Section 4.3 treats the complete elimination of hoisting activities in the vicinity of the unit. Section 4.4 treats a redesign of pipework in the sense that less connections with measurement instrumentations are designed. Section 4.5 treats the redesign of pipework in the sense that less pipework is installed. Section 4.6 treats the complete elimination of corrosion as a factor in all equipment. Section 4.7 treats improved maintenance operations for the centrifugal pump. 

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