Settling pits

The normally good lubricating qualities of mud can be lost if cuttings, particularly fine sand, are not effectively separated from the mud. Adequate settling pits and shale shakers usually eliminate this trouble. Desanders are used occasionally. 

A mud rotary rig cuts a borehole by rotating a bit into the formation materials and removing the cuttings by continuous circulation of a drilling fluid. In a conventional rotary system, mud is pumped down through the drill pipe and out through nozzles in the bit. The mud flows upward in the annular space around the drill pipe to the surface, where it is channeled into a settling pit and a... 

Most acetylene generation from calcium carbide uses one of the wet processes and produces a milk of lime containing 10 to 20 % by weight of calcium hydroxide. The milk is thickened in settling pits to produce either a thick milk of lime or... 

In wet generators, the carbide is added to an excess of water and an impure milk of lime is produced. The milk may be used on site (e.g. for effluent treatment), or it may be fed to settling pits. The resulting lime putty, or carbide dough is then sold as an inferior grade of slaked lime (see also section 22.9). 

PVC powder can be lost in centrifuge and scrubber effluent and by overfilling stock tanks and from pipeline leaks. It is important that all plant drains which are likely to contain PVC are directed to settling pits where flocculation treatment can be used so that the final discharge is free of PVC. All wet waste is collected and reclaimed as second- or third-grade material for use in noncritical applications such as one-trip horticultural products and fencing. 

There may be times when there are open trenches or excavations on the site. The scale and duration of excavating and trenching is site-specific. On some drilling sites, a belowground-level cellar may be excavated. This is where the main borehole is to be drilled. A reserve pit and settling pits are often excavated and are used for water or drilling fluid (mud) discharges. 

Leaky valves are also a cause of erosion. Most turbine erosion-corrosion problems come from damage that takes place when the unit is not running. A shght steam leak into the turbine will let the steam condense inside the turbine, and salt from the boiler water will settle on the inside surfaces and cause pitting, even of the stainless blading. There must be two valves with a drain between them, i.e., a block valve on the header and an open drain in the line before it reaches the closed trip-throttle valve. 

Prevailing wind locate hazardous vents, burning flares, waste burning pits, waste settling ponds down-wind of plant proper. 

Suction lines are often partly filled by settled sand and by debris from the pits, causing the pump to hammer at abnormally low speeds. Frequent inspection and cleaning of the suction manifold is required. The suction strainer can also be a liability if it is not cleaned frequently. 

Let the mud circulate through all pits (tanks) available to increase the settling time do not agitate the mud. 

Flat-bottomed storage tanks tend to suffer pitting corrosion beneath deposits or sediments which settle out. Storage tanks may be emptied infrequently and may not experience sufficient agitation or flow to remove such deposits. 

Deposit attack and pitting When water speeds are low and deposits settle on the surface (particularly at water speeds below about 1 m/s), pitting of copper and copper alloys is liable to occur by differential aeration effects. 

Where feed lines have short pipe runs, where hot wells or FW tanks are of small volume, or when FW is too cold, there often is insufficient time for full DO scavenging to take place, even when using catalyzed scavengers. The inevitable result of this lack of contact time is the formation of oxygen-induced corrosion products, which by various secondary mechanisms may settle out to form permanent deposits within the boiler system. These deposits may develop in several forms (e.g., where DO removal is particularly poor, they often appear as reddish tubercles of hematite covering sites where pitting corrosion is active). Active pitting corrosion combined with the presence of waterside deposits ultimately may lead to tube failure in a boiler or other item of system equipment and result in a system shutdown. 

Settle, F.A., Laboratory automation and LIMS The continuing drama of Pit-... 

All fixed fire suppression system control valves should be located out of the fire hazard area but still within reach of manual activation. For high hazard areas (such as offshore facilities), dual feeds to fire suppression systems should be considered from opposite areas. For onshore facilities, firewater isolation valve handles should not be contained within a valve pit or a below grade enclosure within the vicinity of hydrocarbon process facilities, since heavy process vapors travel from the process and may settle inside. 

Table I. Concentration Difference in Liquid Samples from Agronomy Pit when Settling, Centrifuging and Filtration are Employed...

---