Structural steel protection, processing

Insulators or materials with low heat conduction are often used for fire protection coatings and thermal insulation. This thermal barrier prevents heat reaching and damaging structural steel and process vessels. 

The main application of sprayed aluminium is for the protection of structural steel, and the process can also be utilised to protect high-strength aluminium alloys. The process has the important advantage that it can be carried out on site. 

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. 

Horizontal, stressed primary structural steel members can also be protected by water spray directed onto the surfaces exposed to fire. Stressed primary horizontal members may include beams connecting perimeter columns as well as those supporting significant equipment loads or connecting to other important vertical members of the process structure. 

There are other engineering factors that affect the fire and explosion hazard, e.g., engineering standards of the structural steel and foundations, process equipment, heat exchangers, feeding system, fan and blowers, storage vessels, electrical equipment, instruments, and fire protection and safety equipment. Considerable assistance in design also can be obtained from relevant codes of practice. The responsibility for safe operation rests with the manufacturers of equipment and products as required by national law (e.g.. Factories Act and Health and Safety at Work Act in the United Kingdom). 

With durable anodes, such as the DSA , current is applied from an external power supply to achieve cathodic protection. However, it is necessary to optimize the electrode geometry of this system to realize uniform current distribution. Cathodic protection is widely used to protect pipelines, buried steel structures, steel reinforcement in concrete, and chemical process equipment. 

Electrochemical Chloride Removal and Protection of Concrete Bridge Components Laboratory Studies. Investigates the feasibility of electrochemical removal and concurrent protection as a rehabilitation option for concrete bridge structures. Chloride removal process procedures were developed, and the effects of the process on structure concrete integrity and reinforcing steel were studied. 201 pages. SHRP-S-657... 

Coatings such as a zinc silicate primer covered with a layer of an epoxy-based polymer are routinely applied to steel structures to protect them against corrosion. However, cracks or flaws in the coating expose Fe which then undergoes oxidation in an anodic process. To prevent this, a second protection system is put in place cathodic protection. By placing a block of a more electropositive metal on the surface, this second metal is preferentially oxidized. This is the same principle as the use of zinc in galvanized steel (see Section 6.7). From Table 8.1, you can see why Zn, A1 and Mg (or alloys of these metals) are typically chosen as sacrificial anodes. The most electropositive metals (Li, Na, K and Ca) are unsuitable because they react with cold water. The relevant half-equations (at pH 7) are now ... 

The scope of this book is heavy-duty protective coatings used to protect structural steel, infrastructure components made of steel, and heavy steel process equipment. The areas covered by this book have been chosen to reflect the daily concerns and choices faced by maintenance engineers who use heavy-duty coating, including ... 

Cathodic protection is widely used on small to extremely large structures to protect metals and particularly steel against corrosion. This can often be accomplished by using a protective current that is either generated by a power supply in what is called impressed current cathodic protection (ICCP) or by using another metal that corrodes more readily than the metal being protected and therefore is sacrificed is the process. Chapter 13 provides a much detailed discussion of this important technique. 

The decision to cathodically protect reinforced concrete structures depends on technical and economic considerations. Cathodic protection is not an economic process for small area displacements of the concrete due to corrosion of the reinforcing steel arising from insufficient concrete covering. On the other hand, the... 

Organic coatings are applied mainly to mild steel structures and equipment. They are also used on aluminum, zinc-sprayed and galvanized steel, but to a lesser extent. The applications for organic coatings can be divided into three areas corrosion by atmospheric pollution, protection from splash by process liquors, and linings for immersion in process liquors [70-74]. 

Sprinkler and water spray installations-Many process and storage area buildings should be protected by automatic sprinkler systems. The size and arrangement for water supply are dependent upon the nature of the hazard and the degree of protection desired. Water spray installations are particularly adapted for cooling uninsulated steel structures, elevated pipe lines, vessels, spheres, and similar plant installations. 

A wide range of paints and other organic coatings is used for the protection of mild steel structures. Paints are used mainly for protection from atmospheric corrosion. Special chemically resistant paints have been developed for use on chemical process equipment. Chlorinated rubber paints and epoxy-based paints are used. In the application of paints and other coatings, good surface preparation is essential to ensure good adhesion of the paint film or coating. 

Steel, aluminum, concrete, and other materials that form part of a process or building frame are subject to structural failure when exposed to fire. Bare metal elements are particularly susceptible to damage. A structural member undergoes any combination of three basic types of stress compression, tension, and shear. The time to failure of the structural member will depend on the amount and type of heat flux (i.e., radiation, convection, or conduction), and the nature of the exposure (one-sided flame impingement, flame immersion, etc.). Cooling effects from suppression systems and effects of passive fire protection will reduce the impact. 

Perimeter vertical columns and other columns that support significant equipment or building loads are usually selected for protection. Typically, water spray is applied to each column with sufficient flow rate to wet and cool the exposed steel surfaces. The water spray is directed onto the column s web at each level of the process structure, or at every 15 ft (4.6 m) of elevation, on alternate sides of the column. 

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