Structural steel protection

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. 

Sprinkler Protection for Medium to Small Processing Facilities 

Flash Point Fleated To/Above Flash Point Room or Equipment Explosion Elazard Sprinkler Density gpm/IV (Ipm/m ) Sprinkler Temp. Rating °F (C) Area of Demand (m ) Manual Elose Streams gpm (Ipm) Dura- tion min 

Several different materials and installation systems are available and include various types of proprietary materials, plasters containing perlite or ver-miculite, concrete mixtures, or lightweight concretes. The selected material and installation system, encasement, or surface application should provide protection for the expected fire duration. For more information refer to Chapter 7, Section 7.3.2. 

The material and its installation should be designed to protect for a specific time period. For hydrocarbon fire exposure materials and their installation are generally tested to either UL 1 709 or ASTM El 529 to determine time-to-failure of different thicknesses and installation methods. It should be noted that the fire resistance rating is a measure of the ability of the installed material to withstand a specific standard fire. While these conditions closely match those in any given hydrocarbon fire, during actual fires the material may be exposed to conditions that may be more or less thermal intense, thus it can be expected to retain its integrity for a greater or lesser time. 

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Water Spray and Fireproofing for Structural Steel Protection... 

The protection potentials for seawater are described in Section 2.4. In pipelines and harbor installations, there is no limiting negative potential t/ for uncoated earbon steel or for steel provided with thiek eoatings over 1 mm, with yield points up to 800 N mm". With dynamieally highly loaded structures, the protection potential ranges in Table 16-2 should be adhered to as in the regulations [1-3] because of the risk of hydrogen-induced stress corrosion (see Section 2.3.4). 

Protection. Forged parts, rolled structural steel shapes and plates, and castings shall be cleaned, primed, and painted with a good commercial paint or other specified coating before shipment. Machined surfaces shall be protected with a suitable lubricant or compound. 

Saponification Paints are most commonly used to protect steel from corrosion by seawater in marine applications and soil in the case of buried structures. Additional protection is often supplied by the application of cathodic protection to the steel. Any paint coating used in conjunction with cathodic protection must be resistant to the alkali which is produced on the steel at defect sites in the coating. The amount of alkali generated depends on the potential to which the steel is polarized. Some paint binders such as alkyds and vinyl ester are very susceptible to saponification, and should not be used on cathodically protected structures. Cathodic disbondment testing should be undertaken if the relevant information is not available. 

The first three authors were concerned with the rusting of motorcar bodies. They found that the rusts formed on steel under sheltered and exposed conditions, respectively, differed markedly in chemical composition, structure and protective properties. The second paper gives the results of exposure tests in many different indoor atmospheres, from which the following representative rates of rusting over one year are taken. 

Structural steels are frequently protected from corrosion by means of a paint primer, but these materials can have an adverse effect on the... 

It is essential to ensure adequate current distribution such that all of the exposed structure remains protected particularly important, for example, for the nodes of an offshore steel structure. Similarly, over-protection should be avoided. Thus, sacrificial anodes need to be distributed to ensure that the protection potential over the whole structure is achieved. 

Bailey, J. C. and Porter, F. C., Sprayed Metal Coatings for the Protection of Structural Steel-A Fresh Appraisal, Const. Steel, 12-19, Feb (1972) (Reprinted by American Welding Society)... 

Klinge, R., Sprayed Zinc and Aluminium Coatings for the Protection of Structural Steel in Scandinavia . Proc. 8th Ini. Thermal Spray. Conf., American Welding Society, pp. 203-213 (1976)... 

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... 

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 outstanding virtue of zinc-rich paints is simplicity in application. No special equipment is required and the operation can, of course, be carried out on site, large or small structures being equally suitable for treatment. While there is some evidence that the zinc-rich paints will reduce iron oxides remaining on the steel surface, proper surface preparation is as important here as with traditional paints if the best results are to be achieved. The main use of zinc-rich paints is to protect structural steel-work, ships hulls, and vulnerable parts of car bodies, and to repair damage to other zinc coatings. 

Fancut, F. and Hudson, J. C., for the Protective Coatings (Corrosion) Sub-Committee of B.I.S.R.A., Protective Painting of Structural Steel, Chapman and Hall, London (1957)... 

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... 

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. 

Underwriters Laboratories Inc. (UL), UL 1709, Safety Rapid Rise Fire Tests of Protective Materials for Structural Steel. First Edition, UL, Northbrook, IL, 1991. 

Rapid Rise Fire Tests of Protection Materials for Structural Steel, 1989. 

Applications for structural steel in blast resistant design include beams and columns for the support of vertical loads, braced and rigid frames for the support of vertical and horizontal loads, and specialized elements such as doors, window frames, decking, and protection for duct openings. For lower blast loads, steel siding can be used. 

Structural steel shall be protected with a 3-hour rated fire resistive system per UL 1709. 

ASTM E 1529 Standard Test Methods for Determining Effects of Large Eiydrocarbon Pool Fires on Structural Members and Assemblies and Underwriters Laboratories Inc. 1709 Standard for Rapid Rise Fire Tests of Protection Materials for Structural Steel are two tests which are used to evaluate the performance of structures, equipment, and protective materials to hydrocarbon fires (see Figure 5-17). 

Jet fire flame impingement on vessels or structural steel that are not protected for 15 minutes... 

Fire resistant insulating material can provide passive protection for both vertical and horizontal structural steel members. The level or rating of fire resistance should be consistent to the expected fire duration. Where only fire resistant insulating material will be used, the material and its installation system should be specified to have a 2- to 3-hour fire rating (UL 1709). In applications using a combination of fixed water spray or sprinkler protection and fire resistant insulation, a 1- to 2-hour fire rating (UL 1709) is frequently specified for the fireproofing. 

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. 

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. 

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. 

A generalized comparison of equivalent fire protection for structural steel using water spray rates recommended in NFPA 15 and fire-resistive insulation used alone or in combination is provided in Table 8-9 (NFPA 15). 

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