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Controls
Published in Carl Bozzuto, Boiler Operator's Handbook, 2021
Sensing lines for pressure gauges can affect the quality of their reading and, in some cases, can produce some operating problems if not installed and maintained properly. First, there is the matter of the size of the sensing connection. None should be smaller than 1/2 inch nominal pipe size (NPS). A 1/2 inch schedule 80 pipe nipple and valve is strong enough for most people to stand on without damage. Anything smaller is simply looking for trouble. Sensing connections should be made at the side or top of process lines to limit any debris settling into the smaller line and blocking it. The connection should be isolated with a valve as close as reasonable. Only provide enough room for a hand to get at the valve handle and make allowances for insulation. After the isolating valve, smaller piping or tubing can be installed from the connection to the gauge. If it gets broken, quickly shut the valve.
Water/Wastewater Conveyance
Published in Frank R. Spellman, Handbook of Water and Wastewater Treatment Plant Operations, 2020
In the continuing effort to standardize pipe size and the wall thickness of pipe, the designation nominal pipe size (NPS) replaced the iron pipe size designation, and the term schedule (SCH) was developed to specify the nominal wall thickness of pipe. The NPS diameter (approximate dimensionless designator of pipe size) is generally somewhat different from its actual diameter. For example, the pipe we refer to as a “3-in. diameter pipe” has an actual O.D. of 3.5 in., while the actual O.D. of a “12-in. pipe” may be .075 in. greater (i.e., 12.750 in.) than the nominal diameter. On the other hand, a pipe 14 in. or greater in diameter has an actual O.D. equal to the nominal size. The inside diameter will depend upon the pipe wall thickness specified by the schedule number.
Valves, Pumps and Pipes
Published in Anders Andersson, Measurement Technology for Process Automation, 2017
Pipe sizes are normalised. There are many standards, some general and some application specific (e.g. those used in the food industry). Each pipe and connection size is named after its nominal diameter; however, measures vary with pressure rating. For a pipe, it is the outer diameter that is equal for all pressure ratings in a specific dimension, and as the pipe wall is thicker in pipes suitable for high pressure, the inner diameter will be smaller in a high-pressure pipe. This is of importance for some instruments; for example, vortex-type flow meters need to be adapted not only to nominal diameter but also to pressure class. There are two common pipe size standards: the American (ANSI/ASME/API) standard with sizes stated in inches, and the European/German (DIN) system with dimensions in millimetres. In the American system, the pipe diameter is known as the ‘nominal pipe size’ (NPS) or ‘nominal bore’ (NB), and wall thickness is categorised by the ‘Schedule’. In the European system, it is known as the ‘nominal diameter’ (DN). Each nominal diameter is available in different wall thicknesses, to match working pressure and temperature. Pipes can be made of different materials; mild steel, stainless steel, copper and plastic pipes are commonly available. Steel pipes can be longitudinal welded, spiral welded or seamless. In a precise measuring situation, watch out for welded pipes that are not smooth inside as these can affect flow profile. The pipe needs to be round if a clamp-on flow meter is used. Even small imperfections in roundness can affect the measuring accuracy.
Dissimilar welding between piping and valves in the offshore oil and gas industry
Published in Welding International, 2021
This type of pipe joint is normally used for small pipe diameters in nominal pipe size (NPS) 2” or smaller. The thread end piping is a male part, which is inserted into a female part of the valve or fitting. The fitting or a valve suitable for threaded connection to the piping follows ASME standards just like socket welding [22]. The dimensional standards for taper pipe threads are given in the ASME B 1.20.1 standard [23,24]. The threaded connection is subject to leakage due to temperature change, vibration, and high stress concentration, and there is a high risk of corrosion [23]. This type of connection is used in low cost, non-critical applications such as water in onshore facilities including refineries and petrochemical plants [23]. On the other hand, threaded piping connections are not used for subsea and topside offshore sectors of the oil and gas industry because failure of facilities including piping is less tolerated in the offshore sector.