2　Terminology

2.0.1　Nominal Diameter

Nominal diameter is represented by character DN plus integral numbers and indicates the caliber size of the pipe components such as pipes,pipe fittings,and valves.Its unit is mm.

2.0.2　Nominal Pressure Nominal pressure is represented by character PN plus numbers and indicates the allowable pressure rating of pipes,pipe fittings and valves at the specified temperature.Its unit is MPa.

2.0.3　Pipe

Pipe is the confined and consistent segment continuum used for the conveyance of medium or medium pressure.

2.0.4　Pipe fittings

Pipe fittings are the general designation of the parts and components which are connected with pipes and constitute the system,including elbows,bends,tees,reducers,compensators,stub tubes,flanges and seals,plugs,heads and so on.

2.0.5　Pipe Accessories

Pipe accessories are support parts in piping system,including supports and hangers,fastener,reinforcement parts,gaskets and so on.

2.0.6　Valve

Valves are general term for the devices with free mechanisms for controlling the flowing status of the medium in the pipe.

2.0.7　Compensator

Compensators are the devices connected with the pipes which can absorb and compensate the displacement caused by thermal expansion and contraction and other displacement of the pipes.

2.0.8　Bends

Bends are the pipe segments with the required radian and shape after bending of pipes.

2.0.9　Elbows

Elbows are the pipe fittings with the bending radius not being more than 2D and the length of the straight section being less than 1D.

2.0.10　Welding Elbows

Two or more straight pipe segments are welded together in the plane bisecting the angle of junction which form the welding elbow,also known as the miter elbow or dried shrimp-shaped elbow.

2.0.11　Calculated Thickness of Straight Pipe

The minimum wall thickness of straight pipes added with the minus deviation value of straight pipe thickness is called calculated thickness of straight pipe.

2.0.12　Supervision Section of Pipe

Supervision section of pipe is the section for metallograph and hardness tracking inspection on the steam pipe.

2.0.13　Creep Measurement Point

Creep measurement point is the device or marker set on the supervision section or steam pipe for measuring the creep deformation of the pipe.

2.0.14　Critical State of Water

In a tight vessel,when the steam pressure reaches 22.115MPa and the saturation temperature reaches 374.12℃,there is no difference between the saturated steam and saturated water.Namely,all of the water will vaporize immediately when it is heated to 374.12℃at this pressure.The saturated steam will become superheated steam when further heated.This state is called the critical point of water.The pressure is called the critical pressure.The temperature is called the critical temperature.When the temperature is above 374.12℃,whatever the pressure is,the steam can not be liquefied.

2.0.15　Pipe Grade

The pipes of the power plant are classified by the design pressure"P"as the main parameter.It can be implemented according to Table 2.0.15.

2.0.16　Roundness

Roundness is the ratio of the difference between the maximum and the minimum outer diameters and nominal outer diameter on the same circular section of the pipe bending part.

2.0.17　Wave Degree

Wave degree is the ratio of the wave height"h"and the outer diameter"Do".