Cast-iron-lined Main

A chamber in service for a 10-yr period in which rebuilt valves were present was found to be saturated with chlorides and phosphates. The chloride caused the corrosion of bolts to such an extent that the chamber was leaking. The chamber housed 24-inch and 16-inch valves along with air drain-out. All the bolts on the valves required replacement. Furthermore, the aluminum ladder rungs were completely corroded. 

The use of wax taping and magnesium anodes resulted in very little corrosion, requiring only normal operating maintenance and inspection of the chamber for valve integrity. 

ASTM G 97, Standard Current Efficiency Test for Magnesium 

RP0169-96, NACE Book of Standards, Standard Recommended Practices 

Atkinson and H. Van Droffelaar, Corrosion and Its Control, An introduction to the Subject, 2nd Edition, NACE International Houston, 1995, pp. 270, 280, 281. 

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Two examples of cathodic protection are discussed protection of a ductile iron main protection of a cast-iron-lined main. 

Selected Examples of Failure and Their Prevention Cathodic protection of water mains Here two examples of cathodic protection (i) ductile iron main and (ii) cast-iron-lined main are discussed. 

Polycyclic aromatic hydrocarbons (PAHs) are usually only found in drinking-water as a consequence of leaching from coal-tar linings on cast-iron water mains. The PAH of greatest concern is benzo(a)pyrene, but the most commonly encountered is fluoranthene. Benzo(a)pyrene is normally only detected at significant concentrations in water when particles of coal tar are present,... 

One production line of a paper mill consists according the size and the quality of the produced paper sometimes from more than 50 steam drums to dry and flatten the produced paper. These drums (cylinders with flat bottoms, see figure 1) will be used with a steam pressure up to 500 kPa (5 bar) and additionally with a rotation speed up 1200 m.min the material is mainly grey cast iron (with lamellar graphite). The diameters can reach up to 2.2 m and the cylindrical lengths up to 10 m. For the specific flattening drums the cyhndrical diameters can be up to 5 m and more. 

Deterioration of water pipe fittings such as service saddles contributes to water main failures. This type of failure may be due to galvanic corrosion since the pipe is cast or ductile iron, saddle is either bronze, steel or cast iron and the service line is made of copper. 

The main emphasis in power line corrosion control is to select materials resistant to a specific environmental attack and to galvanize ferrous materijils (carbon steel and cast iron). This approach is used in the design of new lines and is supplemented by selective use of coatings and cathodic (galvanic) protection. The in-service methods are hmited to apphcation of coatings, cathodic protection, juid inhibitors. 

On smaller decanters, the frame has often been made from cast iron. More usually it is fabricated from steel channel or box sections. The frame needs to be a rigid support for the rotating assembly. The surfaces for the main bearing pillow blocks are accurately machined in the same plane, and in line, to ensure no end-to-end misalignment of the rotating assembly, which would cause premature bearing failure. Some manufacturers fill part of the main frames of their larger machines with concrete effectively to form an inertia... 

Are these corrosion cells common The answer is yes. Whenever a copper pipe service line is directly connected to a cast iron gas or water main, a galvanic cell is formed (Fig. 7.19) the soil is the electrolyte, the copper service line is the cathode, the iron (or steel) main is the anode, and the connecting circuit is completed by attaching the line to the main. Such cells may be relatively harmless when the anode or corroding metal occupies a much larger surface than the cathode so that the attack is spread out over a large area. 

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