Nozzle maintenance

A discussion on spraying is incomplete without a discourse on nozzle maintenance and testing. In any coating application, the spray nozzle is the single most critical component. Its performance dictates droplet size control, the quality of the applied film and the reproducibility of the resultant product properties. These include appearance, potency, film coating efficiency, and release characteristics. In retrospective process troubleshooting, spray nozzle performance is often the leading cause of product deviations. 

Figure 12 shows the plan and elevation views of a process unit piping (9). A dmm is supported off the piperack. Heat exchangers are located far enough back from the support columns so that they are accessible and their shell covers can be removed. Pumps are located underneath the piperack, but sufficient room is provided for maintenance equipment to access the motors and to remove the pump if necessary. The motor is always oriented away from the process equipment and located on that side of the piperack. Instmment valve drops are shown supported from the columns. The instmment trays themselves mn on the outside of the support columns. Flat turns are only made from the outside position of the piperack. Nozzle-to-nozzle pipe mns are made whenever possible. Larger lines are located on the outside of the piperack. Connections to nozzles above the rack are made from the top... 

It is not recommended to place an elbow at the suction of any pump (Figure 16-2, next page). This will cause a turbulent flow into the pump. If elbows are needed on both sides of the pump, you should u.se long radius elbows with flow straighteners. You should have 10 pipes diameters before the first elbow on the suction piping (Example If the pump has a 4 inch suction nozzle, you should respect 40 inch of straight pipe before the first suction elbow.) Short radius elbows cause vibrations and pressure imbalances that to lead to wear and maintenance on the pump. 

For centrifugal compressors, nozzle orientation must be specified. If the compressor is on an elevated foundation, the down-nozzle orientation makes maintenance much easier, because major piping does not have to be removed to lift the casing upper half. Figure 11-1 shows an unusual case where all the nozzles are in the upper casing half. 

If there were no removable cover on the front end of the exchanger, it would be designated BES." The second nozzle and pass partition in the front end are discretionary depending upon the shell type. Types A and B bolt onto the shell. In type C, the head cannot be unbolted for maintenance. 

Figure 3-1 (page 19) shows where an end-of-line deflagration flame arrester should he located. It preferably should be installed on a nozzle that is near the outer edge of the tank/vessel roof for ease of accessibility for maintenance and removal. 

There are many examples of increased corrosion at or near nozzles and jets and this is a recurring problem requiring frequent replacement and maintenance. The use of hydrodynamics and, in particular, dimensional group analysis, can show the most important parameters and can indicate the comparative rates of corrosion. 

Maintenance errors. One common error is the failure to remove an isolation blind in a vent line when returning a vessel to service. Even a thin sheet of plastic placed over an open nozzle may be sufficient to allow a vessel-damaging vacuum to De produced (BP, Hazards of Trapped Pressure and Vacuum, 2003). 

The sample probe s vertical stroke can be as long as 100 mm and this, with the in built hquid level sensor, allows a wide range of primary tubes and centrifuge tubes to be held on the trays. Sample racks are automatically transported in the front section of the analyser, which in turn simpHfies maintenance should the nozzle become blocked or if mechanical problems arise. The AUSOOO Series provides precise sample dispensing capabihty. Each of the two sample probes aspirates a volume sufficient for a maximum of four chemistries per sample and dispenses it into eight cuvettes on the twin reactor Hnes. The probes are constructed from water-resistant plastic which minimizes any dilution from wash solution or contamination. The built-in level sensor Hmits the immersion of the probe in the sample. The inside and outside of the probe as well as the level sensor are rinsed after each use to further prevent contamination. 

Newer nonclogging, noncorroding ceramic nozzles have been introduced to the market. These generally help reduce maintenance requirements and are now replacing steel nozzles on existing installations. 

Inspection and Preventive Maintenance As with all water-based extinguishing systems, particularly those installed outside, inspection and preventive maintenance are critical to reliable operation. Detection devices are typically inspected, tested, and maintained quarterly or at a frequency deemed more appropriate for a particular location. The water-spray system itself is typically flow-tested at least annually (NFPA 25, 1995). Because of the nozzles small orifice size, scale and corrosion buildup can compromise flow and spray patterns. The use of strainers and the conduct of flow tests will help minimize this potential problem. As stated earlier, preventive maintenance of the overall water supply and distribution systems is an integral part of a reliable system. 

Water sprays from monitor nozzles and hose lines can be used for vapor mitigation. Tests have been conducted in which monitor nozzles and hose lines have been used to create a chimney effect through which the gas is forced upward and dispersed at a high elevation (Beresford, 1981). Application techniques and flow rates are facility-, installation-, and material-specific. Careful planning, analyses, and testing should be conducted prior to deciding on the use of a mobile water spray as a proven means of mitigation. Preventive maintenance of this equipment is key to reliable operation. Hose lines, typically, are hydrostatically tested annually. Flow tests should also be conducted periodically. 

At this section of the plant in the past, chemical process operators (not maintenance mechanics) handled the tank-filling step in the hydrotest process. Operators would typically drape a fire hose into an oversize roof nozzle and fill the tank from the nearest hydrant. In this case, it was reported the two mechanics asked their maintenance supervisor if they could connect the hose to a flanged lower-valved nozzle on the tank. The supervisor remembers requesting the mechanics to roll a blind flange at the top for venting purposes if they used the lower nozzle for filling. There must have been a miscommunication. Obviously the mechanics failed to understand the dynamics of the filling operation when they chose to open only the two 1/2-inch top vents. 

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