Structural steelwork

Falls to gully positions may be provided by the natural deflections of the roof structure or small slopes to the roof steelwork (e.g. 1 40-1 60). 

No. 12 Paint for the protection of structural steelwork No. 13 Surface preparation for painting... 

Galvanised steelwork buried in the soil in the form of service pipes or structural steelwork withstands attack better than bare steel, except when the soil is more alkaline than pH 9-4 or more acid than pH 2-6. Poorly aerated soils are corrosive to zinc, although they do not necessarily cause pitting. However, soils with fair to good aeration containing high concentrations of chlorides and sulphates may do so. Bare iron may be attacked five... 

Gooch, T. G. and Gregory, E. N., Br. Corros. J., Suppl. issue, Design of Protective Systems for Structural Steelwork, 48 (1968)... 

The proximity of the anodes to structures is also important. For example, if the sacrificial anodes are placed on, or very close to, steel pipework in soil then the output from the face of the anodes next to the steelwork can be severely limited. Alternatively, in high conductivity environments, corrosion products may build up and wedge between the anode and the structure. The resulting stresses can lead to mechanical failure of the anode. On the other hand, when anodes are located at an appreciable distance from the steelwork, part of the potential difference will be consumed in overcoming the environmental resistance between the anode and cathode. 

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. 

Sprayed coatings These are of the greatest importance, particularly for the protection of structural steel or certain aluminium alloys. The metal to be coated must be grit blasted shortly before spraying to provide a clean rough surface. Chilled iron grit is used for most steelwork, while alumina or silicon... 

Aluminium-sprayed steel windows in Sheffield remained in good condition some 17 years after erection. Aluminium-sprayed coating on a steel structure at a steelworks in Sheffield is intact after service for 34 years with paint maintenance at approximately 10-year intervals. 

Stanners, J. F. and Watkins, K. O., Painting of Metal Sprayed Structural Steelwork , British Corrosion Journal, 4 No. 1, 7-14, Jan (1969)... 

BCSA/BSC/PRA/ZDA, Steelwork Corrosion Protection Guide Interior Environments (1982) and Exterior Environments (1986). Z.D.A., London BS 5493, Code of Practice for Protective Coating of Iron and Steel Structures Against Corrosion, B.S.I., London (1977)... 

Paint for structural steelwork is required mainly to prevent corrosion in the presence of moisture. In an industrial atmosphere this moisture may carry acids and in a marine atmosphere this moisture may carry chlorides. Paint is therefore required to prevent contact between steel and corrosive electrolytes, and to stifle corrosion, should it arise as a result of mechanical damage or breakdown of the coating through age and exposure. 

In general, interior steelwork is exposed to less severe conditions than exterior, but in some chemical factories the reverse is true and here special types of paint are needed. Much structural steel is encased in concrete it is therefore hidden from view and is given some protection while the concrete remains alkaline. Where the concrete is thick, corrosion may be delayed, but as the concrete becomes carbonated and particularly if it is penetrated by acidic rain water, the metal will corrode. In general it is advisable that steel which is to be encased in concrete, especially for industrial plants, should... 

The costing of painting structural steelwork is a complex subject. The main items of costing are ... 

Paints used for protecting the bottoms of ships encounter conditions not met by structural steelwork. The corrosion of steel immersed in sea-water with an ample supply of dissolved oxygen proceeds by an electrochemical mechanism whereby excess hydroxyl ions are formed at the cathodic areas. Consequently, paints for use on steel immersed in sea-water (pH 8-0-8-2) must resist alkaline conditions, i.e. media such as linseed oil which are readily saponified must not be used. In addition, the paint films should have a high electrical resistance to impede the flow of corrosion currents between the metal and the water. Paints used on structural steelwork ashore do not meet these requirements. It should be particularly noted that the well-known structural steel priming paint, i.e. red lead in linseed oil, is not suitable for use on ships bottoms. Conventional protective paints are based on phenolic media, pitches and bitumens, but in recent years high performance paints based on the newer types of non-saponifiable resins such as epoxies. 

In considering exposure tests, whether in the form of laboratory, field or service tests it is important to consider the purpose of the test and the relevance of the data to the anti-corrosion function of the coating. Thus, in the case of paint coatings, factors such as gloss deterioration, chalking and colour retention are of considerable importance in some industries, for example the automotive industry, but perhaps of minor importance in the painting of structural steelwork. These assessment factors can nevertheless be of significance since they may be the precursors of corrosion of the basis metal. 

Within the furnace section is the furnace structural system (which includes all necessary supporting steelwork, the refractory, and insulation) and the combustion system (which includes fuel and air delivery systems, burners, and ash handling components). The combustion system largely determines the basic boiler configuration. 

To protect against structural failure, water-deluge systems are usually installed to keep vessels and structural steelwork cool in a fire. 

The brackets, and supporting steel work, can be designed using the usual methods for structural steelwork. Suitable methods are given by Bednar (1986) and Moss (2003). 

Open, structural steelwork, buildings are normally used for process equipment closed buildings are only used for process operations that require protection from the weather. 

All fasteners (nuts, bolts, etc.) and other unpainted structural elements to be 316L or 304L stainless steel depending on the application. Protective coating for structural steelwork and carbon steel or ductile cast iron plant items—to be developed. All spill containment to be 304L stainless steel. 

Wetted instrument parts and pockets generally in accordance with wetted plant items in applicable area. Transmitter housings generally coated as structural steelwork above or constructed from 304L stainless steel according to availability and life-cycle cost. Cable insulation to be PVC, and carbon steel conduit (coated in accordance with guidance above) to be employed throughout. 

The required protection may be obtained by active, passive, or a combination of both protection systems. For example, steel support located in a fire exposed area within process unit battery limits may be protected by either a fixed water spray system or the application of fire resistant insulating material to the steelwork or possibly both. Note Passive protection is generally the preferable method for protecting structural steel. 

Fire protection for structural steelwork can be provided by water spray that cools and wets fire exposed surfaces. This active form of fire protection can be used on vertical structural steel columns, horizontal supports and other steelwork. 

Fixed water spray systems designed on an area coverage basis may also be used to wet/cool structural steel supports. In this case, the placement of discharge nozzles should be close, usually within 4 ft (1.2 m) of the steelwork being protected. Alternatively additional nozzles or a separate system may be provided. 

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