Technical Terms of Piping Technology
From DN and PN through flanges and gaskets to the superheater coil – the most important terms explained briefly and clearly.
Pipes & key figures
DN (nominal diameter)
Diamètre Nominal – dimensionless key figure for the approximate inside diameter of a pipeline or valve, e.g. DN 100. Serves to match components that belong together.
PN (pressure rating)
Pression Nominale – dimensionless key figure for the permissible nominal pressure of a component at reference temperature, e.g. PN 16 = 16 bar. As the temperature rises, the permissible pressure falls.
Schedule (Sch.)
Key figure for pipe wall thickness standardised to ASME B36.10/B36.19, e.g. Sch. 40 or Sch. 80. Higher number = greater wall thickness.
Seamless / welded
Seamless pipes are manufactured without a longitudinal weld and are the first choice at high pressure/temperature; welded pipes are more economical and sufficient for many applications.
Heavy wall
Pipe with increased wall thickness for higher pressures and loads – as opposed to standard wall.
Connections & fittings
Weld-neck flange
Flange that is butt-welded to the pipe – the most robust design for high pressures and temperatures (EN 1092-1, DIN 2627–2638).
Blind flange
Flange without a bore that tightly seals off a line or a branch.
Loose flange
Flange that rotates freely on a collar – makes it easier to align the bolt holes.
Pipe bend
Fitting for changing the direction of the line, usually 90° or 45°, as a 3D or 5D radius, seamless or welded (DIN 2605 / EN 10253).
Reducer
Fitting for the transition between two nominal diameters, concentric or eccentric (DIN 2616 / EN 10253).
Tee
Fitting for a branch at a right angle (DIN 2615 / EN 10253).
Cap
Fitting for tightly closing off a pipe end (DIN 2617).
Valves & gaskets
Shut-off valve
Valve for fully opening or closing a line – e.g. gate valve, ball valve or butterfly valve.
Actuator
Drive for operating a valve, pneumatic or electric – for remote control and regulation.
Flat gasket
Flat gasket for flange connections at low to medium pressure, e.g. of PTFE or graphite.
Spiral wound gasket
Spirally wound metal gasket with a soft filler – robust under changing pressure and temperature.
Materials, standards & power plant
Creep-resistant steel
Steel for use at elevated temperatures, for example in steam lines and boilers. Chromium-molybdenum-alloyed grades such as 16Mo3, 13CrMo4-5 and 10CrMo9-10 retain their strength under heat.
Inspection certificate 3.1
Inspection certificate 3.1 to EN 10204 with batch-specific test results, confirmed by an inspection department independent of the manufacturing department – standard for safety-relevant applications.
Stud bolt
Double-ended bolt with two nuts for flange connections – can be tightened evenly; strength classes 8.8/10.9 (steel) or A2/A4 (stainless steel).
Superheater coil
Bent tube string of creep-resistant boiler tubes in which steam is heated beyond the saturated-steam temperature – manufactured to drawing.
Tube sheet
Drilled plate in which the boiler tubes end; the tubes are rolled into or welded into the hole pattern (e.g. in a three-pass boiler).
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