Steels continued structural

Execution. In the execution phase, the CP system is applied to the structure following the design. During the work, the complete concrete surface is checked for cracking, delaminations, cover depth, steel continuity and the presence of metal objects that might cause short circuits. If necessary, continuity is provided and metal objects are connected to the reinforcement. Subsequently the cracked and spalled areas are removed and repaired. The reference electrodes and other monitoring probes are embedded. Then the anode is applied, with overlay or top coat as designed. All electrical coimections are made and the power source is installed. 

Examples of marine foundation types—(a) t) cal piled steel jacket structure, (b) typical gravity structures (i) Co eep and (ii) Howard-Doris, (c) hybrid sted gravity structure (i) RDL hybrid and (ii) sandpooL (Continued)... 

By virtue of its basic size and the relative thinness of its component make-up a liner requires continuous structural support in all directions in order to withstand the loading from thermal and pressure conditions in a reactor and still remain Impermeable. Present liners are therefore usually firmly attached to and fully supported by the concrete structure of the PCRV. Due to this positive attachment, the liner is subjected to the stresses and strains Imparted to it by the PCRV during initial prestressing and, later, by movements of the PCRV due to the operating condition of the reactor. To ensure even distribution of these movements across the full size of the liner, attachment of the liner to the concrete is achieved by the embedment of a combination of steel sections and a multitude of studs or hook anchors. See figure 9. 

Concrete overlays have been used as a protection against reinforcing steel corrosion in new bridges. In general, the overlays are susceptible to cracking, especially on continuous structures, though this is a characteristic of all rigid overlays. ... 

Cathodic protection is by far the most versatile method of corrosion control, since it is applicable to any electrically continuous structure within a suitable electrolyte. Inasmuch as the steel embedded in concrete, and not the concrete itself, requires the protection from metallic corrosion, damp concrete serves as a suitable electrolyte, and even structures exposed to the atmosphere, such as bridge decks, can be protected cathodically. 

Small batch retorts, heated electrically or hy combustion, are widely used as carburizing furnaces and are applicable also to chemic processes involving the heat treating of particulate sohds. These are mounted on a structural-steel base, complete with cyhnder, furnace, drive motor, burner, etc. Units are commercially av able in diameters from 0.24 to 1.25 m and lengths of 1 to 2 m. Continuous retorts with helical internal spirals are employed for metal-heat-treating purposes. Precise retention control is maintained in these operations. Standard diameters are 0.33, 0.5, and 0.67 m with effec tive lengths up... 

The requirements (a) to (c) are obligatory for all types of coating and all objects to be protected for example, they are well known in the protection of steel structures. The objects discussed in this handbook are continuously in contact with electrolytes. For this reason in addition, requirement (d) is of great importance and is discussed in detail below. 

The cathodic protection of reinforcing steel and stray current protection measures assume an extended electrical continuity through the reinforcing steel. This is mostly the case with rod-reinforced concrete structures however it should be verified by resistance measurements of the reinforcing network. To accomplish this, measuring cables should be connected to the reinforcing steel after removal of the concrete at different points widely separated from each other. To avoid contact resistances, the steel must be completely cleaned of rust at the contact points. 

Scrap steel In some fortunate instances a disused pipeline or other metal structure in close proximity to the project requiring cathodic protection may be used. However, it is essential in cases of scrap steel or iron groundbeds to ensure that the steelwork is completely electrically continuous, and multiple cable connections to various parts of the groundbed must be used to ensure a sufficient life. Preferential corrosion can take place in the vicinity of cable connections resulting in early electrical disconnection, hence the necessity for multiple connections. 

In the Forth, Severn and many other suspension bridges, zinc coatings have an important function. The whole main structure is of steel and has been zinc-sprayed on the external surfaces, while the main cable and hanger ropes have been coated by continuous hot-dip galvanising. Case histories of galvanised multi-truss bridges cover more than 30 years. 

The structures and phase transformations observed in steels have been dealt with in some detail not only because of the great practical importance of steels, but also because reactions similar to those occurring in steels are also observed in many other alloy systems. In particular, diifusionless transformations (austenite -> martensite), continuous precipitation (austenite -> pearlite) and discontinuous precipitation (austenite -> bainite and tempering of martensite) are fairly common in other alloy systems. 

Its manufacturing is done by winding continuous strands of plastic-impregnated glass fiber around a steel mandrel at a precisely controlled helix angle, under controlled tension. A cross-sectional view of an RP layup is shown in Fig. 4-2(d). As seen, the structural wall of the pipe is made up of con-... 

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