Roof prevention

Fig. 3.5. Large car-hearth furnace such as used for stress-relieving large vessels. The fiber-lined 90° flues avoid black hole cold spots in the furnace roof preventing uneven load temperature. Courtesy of Hal Roach Construction Co.

Figure 9.2 Floating roofs and flexible membranes can be used to prevent the release of material. (From Smith and Petela, The Chemical Engineer, no. 517, 9 April, 1992 reproduced by permission of the Institution of Chemical Engineers.)...

Also, maintenance workers should inspect roof penetrations and the installation of equipment on roofs during constmction. Because the maintenance department is responsible when the roof leaks, their inspection of roof penetrations during constmction can prevent future problems. Maintenance must also make sure that the roof was not damaged during constmction. 

Ba.lla.sted. A ballasted roof assembly consists of a membrane or membrane and substrate material (insulation, sHp sheet, etc) loosely laid over a deck with the assembly held in place using ballast. A minimum ballast weight of 48.9 kg/m or 10 pounds per square foot (PSF) is used. The ballast can consist of smooth rounded stone, cmshed stone (a separator sheet must be used between the cmshed stone and the membrane), or pavers (both standard and lightweight). Both stone and pavers come in a wide variety of colors. The membrane is affixed to the building only at the deck perimeter (roof edge) and at various penetrations. Wall and penetration flashings are typically fuUy adhered and sealed to prevent water entry into the roof assembly. The maximum slope a ballasted system should be installed over is 16.7 cm/m. 

Sheet form, composed of organic roofing felt, saturated with asphalt and coating on both sides with asphalt compound that may or may not contain mineral stabiHzer, surfaced with powdered talc, mica, or other tine mineral matter to prevent sticking. Classified, in mineral net mass per unit area of roofing, as Type I, 1943 g/m (39.8 lb/100 fC) Type II, 2666 g/m (54.6 lb/100 fC) Type III, 2495 g/m (51.1 lb/100 fC) and Type IV, 1943 g/m (39.8 Ib/lOOfC). 

Factory Mutual provides loss prevention data sheets that explain how to protect buildings from wind damage. Pressure coefficients that define increased uplift at corners and edges adjust the calculated uplift pressures. A laboratory uplift pressure test rates roofing assemblies. An uplift pressure of 2.9 kPa (0.42 psi) must be withstood under FM conditions to meet the Class 1-60 requirements. The FM approval guide is revised aimuaHy (37). 

Eoss Prevention Data, Mdhered or Mechanically Mttached Single-Ply Membrane Roof Systems 1 —29, Eactory Mutual System, Norwood, Mass. 

The bulkhead pan roof has open annular compartments at the periphery to prevent the roof from sinking should a leak develop. 

Fixed-roof atmospheric tanks require vents to prevent pressure changes which would othei wise result from temperature changes and withdrawal or addition of liquid. API Standard 2000, Venting Atmospheric and Low Pressure Storage Tanks, gives practical rules for vent design. The principles of this standard can be applied to fluids other than petroleum products. Excessive losses of volatile liquids, particularly those with flash points below 38°C (100°F), may result from the use of open vents on fixed-roof tanks. Sometimes vents are manifolded and led to a vent tank, or the vapor may be extracted by a recov-eiy system. 

An effective way of preventing vent loss is to use one of the many types of variable-volume tanks. These are built under API Standard 650. They may have floating roofs of the double-deck or the singledeck type. There are hfter-roof types in which the roof either has a sldrt moving up and down in an annular hquid seal or is connected to the tank shell oy a flexible membrane. A fabric expansion chamber housed in a compartment on top of the tank roof also permits variation in volume. 

We now examine three real corrosion problems the protection of pipelines, the selection of a material for a factory roof, and materials for car exhaust systems. The rusting of iron appears in all three case studies, but the best way of overcoming it differs in each. Sometimes the best thing is to change to a new material which does not rust but often economics prevent this, and ways must be found to slow down or stop the rusting reaction. 

When the change of roof is impossible, it is advisable to exchange the air in the tank free space to carbon dioxide which will prevent ignition in the case of sparking. 

Minimize contamination via fewer cross-connections and fewer hose stations. Minimize the number of hoses required in loading/un-loading facilities. Cross-contamination, sometimes even from catalytic amounts of material, can result in undesired hazardous reactions. To prevent contamination due to rainwater and spills, consider storing a material that can react vigorously with water under a roof. 

If primary control by the enclosure is under consideration, the extra wear and tear on electrode holding equipment by the escaping fume must be taken into account. This potential problem is particularly evident on ultra-high-power (UHP) furnaces where the holding equipment would be constantly exposed to high-temperature flame. As a possible solution, the furnace could be equipped with a roof-mounted water-coiled stub stack, which naturally draws fume from the furnace and into the enclosure. This approach would divert the fume and prevent damage to the electrode equipment. 

Another somewhat similar incident occurred when butadiene from a reactor flowed in the wrong direction up a line used for adding emulsifier. The check valve, which should have prevented the flow, was obstructed. The emulsifier tank was in a building and had an open vent. Butadiene came out and exploded. The explosion was heard 15 km away, but damage was minimized by the light construction of the building, w hich ruptured at the junction of the roof and walls [13]. 

The average American home is responsible for more annual pollution than the average car. This often comes as a surprise because the pollution attributed to homes is produced miles away at a power plant or out-of-sight from roof exhaust flues. However, eveiy time someone flips a switch, activates the air conditioning, or takes a shower, pollution is being produced. There will be growing appreciation for energy efficient homes that help prevent pollution. 

Weak roof-to-shell attachment for fixed roof tanks, as per API-Std-650 for Welded Steel Tanks for Oil Storage. The joint fails and excess pressure can be relieved (above the normal design provided). Such tanks do not require additional emergency vent equipment however, it can be provided in order to prevent the roof seam failure with its attendant replacement/ maintenance requirements. This type can only be used outside of a building, not confined. 

A compressor will always give better, more reliable service when enclosed in a building that protects it from cold, dusty, damp, and corrosive conditions. In certain locations, it may be economical to use a roof only, but this is not recommended unless the weather is extremely mild. Even then, it is crucial to prevent rain and windblown debris from entering the moving parts. Subjecting a compressor to adverse inlet conditions will dramatically reduce reliability and significantly increase maintenance requirements. 

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