Main ring

Occasionally all the valves on a ring main would be closed and the pressure in a pump rise to danger point. No one appeared to realize that there was anything wrong with this state of affairs. 

Feeds the Fire-water ring main on platform with water from the sea. 

By time/direction Protective devices responsive to the direction of current flow. These are necessary for parallel feeders or closed ring-main supplies. 

There are two main types of oil-handling system in common use. These are gravity and ring main. 

Ring main systems are of three types hot oil, warm oil and cold oil. Hot oil ring mains circulate oil at atomizing temperature, warm oil ring mains at a temperature between minimum pumping and atomizing temperature, and cold oil ring mains at ambient temperature. 

With some installations, it is possible to maintain circulation during periods when the oil-firing plant is not required to operate. The oil is circulated at reduced temperature to minimize the heat loss from the ring main and, consequently, the amount of heat required to compensate for this loss. The reduced temperature should be such that the increased oil viscosity does not result in an excessive increase in pressure. 

This system is similar to a cold oil ring main but includes provision for heaters in the circuit to maintain oil temperature between minimum handling and atomizing levels. This provides a reduction in oil viscosity and reduces pipe friction. The circulation temperature of the oil should... 

Branch lines transfer oil from a ring main circuit to the oil-burning equipment. Where a residual oil fuel is to be used, there will be some cooling of the oil immediately adjacent to the pipe surfaces and this will show as a small increase in viscosity. To keep this variation to a minimum and so prevent any difficulties in atomization at the oil burner, care should be taken over the length and diameter of branch lines. Provision should always be made to isolate and drain branch lines. 

Pressure drop under streamline flow conditions is directly proportional to the quantity of oil flowing. The effect of reduced flow rate after take-off points, as compared with full flow rate throughout the full length of the pipeline when there is no take-off, should be taken into account to ensure that variation in pressure is within the specified pump output. Special consideration is necessary with gravity and ring main systems serving several take-off points. 

Synthesis by Formation of Heterocyclic Ring Main Features... 

A small but variable proportion of the carotenoids with one or two P-ionone rings (mainly P-carotene) are cleaved in the enterocytes to produce retinol (vitamin A). This process is very tightly controlled, so that too much vitamin A is not produced, although the control mechanism is not clear. Some cleavage of P-carotene can also occur in the liver, but this does not account for the turnover of P-carotene in the body. Small amounts of carotenoids are subject to enterohepatic circulation, but this does not account for losses. 

Table 3 Stereochemistry of natural pheromones containing an epoxy ring (main components) and field attractancy of the synthetic racemate... 

Species Main pheromonal component Stereochemistry of the epoxy ring (main component) ... 

Hydrants should be considered as a backup water supply source to monitors and fixed fire suppression systems. Hydrants should be located on the ring main at intervals to suitably direct water on the fire hazard with a fire hose. Hydrants monitors and hose reels should be placed a minimum of 15 meters (50 ft.) from the hazard they protect for onshore facilities. Hydrants in process areas should be located so that any portion of a process unit can be reached from at least two opposite directions with the use of 76 meters (250 ft), hose lines if the approach is made from the upwind side of the fire. Offshore hydrants are located at the main accessways at the edge of the platform for each module. Normal access into a location should not be impeded by the placement of monitors or hydrants. This is especially important for heavy crane access during maintenance and turnaround activities. 

The out-of-plane R rings are believed to be less strained than the G or E rings, mainly on the chemical basis that another ligand displaces a G ring more easily. 

The case of an electron-withdrawing group in the 2-position has been less thoroughly studied (see, e.g., Mamaev and Shkurko141 and Van Zyl et al.i12). Substitution often occurs in the benzene ring (mainly in the 4-position), but also occurs to some extent in the deactivated 3-position. 

If a sugar contains both an aldehyde and a ketone function, the aldehyde will form rings mainly the composition can be quite complex. Eight monomeric forms (out of a possible 18) were identified in the spectra of each of the pentos-2-uloses.36 The erythro isomer was found to consist, at 23° in D20, of 4.5% of the a-aldopyranose and 20.5% of its hydrate, 4.5% of the / -aldopyr-anose and 38.8% of its hydrate. 10.9% of the a-aldofuranose hydrate, 14.2% of the / -aldofuranose hydrate, 5.2% of the a-ketofuranose hydrate, and 1.1% of the / -ketofuranose hydrate. For the threo isomer, the composition, in the same order, wasfound to beO.9,59.8,1.0,29.1,1.5,1.3,1.0, and 5.4%. These compositions were also determined at 80°. 

The structure of 4 -propyl-4/3,5/3-cthcnopregnanc-3,20-dione (131) as the main product of photochemical [2 + 2] cycloaddition of 1-pentyne to progesterone and 4a,5a-analogue 138 was confirmed by X-ray analysis. The CD data of 131-140 were in agreement with A/B-cis and AfB-trans fusion in 131 and 138, respectively, and with the cyclobutene ring (main perturber of the C=0 n —> jr transition) lying in a (—)-octant of 131 and a (+)-octant of 138323. 

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