HG/T 20514-2014Design code for tracing and insulation of instrument and impulse line (English PDF)

2.0.1 insulation

Measure of providing an insulation layer on the outer wall of equipment and pipelines to reduce heat conduction, in order to reduce the loss of heat or cold of the medium inside them and to prevent scalding or frostbite of persons; general term for heat insulation and cold insulation.

2.0.2 heat insulation

Covering measure taken on the outer surface of equipment, pipelines and accessories to reduce the heat they dissipate to the surrounding environment.

2.0.3 cold insulation

Covering measure taken on the outer surface of low-temperature equipment and pipelines to reduce the heat transferred from the surrounding environment into them and to prevent condensation on their outer walls.

2.0.4 thermal insulation layer

Insulation structure covering the outer surface of equipment and pipelines that plays the main role in keeping the temperature of the medium stable.

2.0.5 moisture resistant insulation layer

Layer of moisture-proof structure provided outside the insulation layer to prevent water or moisture from entering it.

2.0.6 jacketing

Layer of protective structure provided outside the insulation layer or the moisture-proof layer to prevent them from being damaged by external causes.

2.0.7 thermal insulation construction

Structural assembly consisting of the insulation layer, the moisture-proof layer and the protection layer.

2.0.8 insulation material

Material with good thermal insulation performance and other physical properties, used for the purposes of heat insulation, cold insulation, scald prevention, stable operation, etc.

2.0.9 maintain temperature

A certain temperature at which the designed tracing system can keep the traced object under the design conditions.

2.0.10 maximum maintain temperature

The highest temperature at which the electrical heat-tracing system can continuously keep the traced object.

2.0.11 end termination connection

Termination connection of the electrical heat-tracing cable at the end opposite to the power supply end.

2.0.12 electrical heat-tracing

Use of electrical heat-tracing cables or other electrical heating facilities to make up the heat lost by the traced object during service, so as to maintain the temperature of the medium within a certain range.

2.0.13 thermostat controller

Field instrument or temperature switch that can detect and control the temperature of the electrical heat-tracing system or the ambient temperature at the location of the electrical heat-tracing system. It can switch the electrical heat-tracing cable on and off locally, and can also send alarm contact signals externally.

2.0.14 self-regulating cable

Flat strip cable consisting of an electrical heating element, formed by conductive polymer composite material uniformly extruded between two parallel conductive metal cores, together with insulation and sheath. Its output power varies with temperature; it can be cut or extended arbitrarily; it can be laid crossing over itself.

2.0.15 constant wattage cable

Electrical heat-tracing cable consisting of bus wires, insulation layer, heating core, sheath, shielding layer, etc., whose output power per unit length is constant, which can be cut or extended arbitrarily, and which shall not be crossed or overlapped.

3.1 Tracing

3.1.1 Tracing shall be applied to instruments and impulse lines meeting one of the following conditions:

1 Material measuring lines and detecting instruments in which freezing, condensation, crystallization, precipitation or similar phenomena occur at ambient temperature;

2 Instruments that cannot meet the minimum ambient temperature requirement.

3.1.2 For tracing and insulation systems located in an outdoor environment, the ambient temperature shall be taken as the local extreme minimum temperature; for tracing and insulation systems installed indoors, the ambient temperature shall be taken as the minimum indoor temperature.

3.1.3 The tracing of instruments and impulse lines should be selected according to the process tracing method.

3.1.4 Tracing methods are divided into hot water tracing, steam tracing and electrical tracing. The tracing method should be selected in accordance with the following provisions:

1 Hot water tracing should be the first choice of tracing method;

2 Steam tracing may be used where no hot water source is available, or for detecting systems whose requirements cannot be met by hot water tracing;

3 Electrical tracing may be used in places with high requirements for environmental cleanliness, or where precise temperature control, remote control or automatic control of the tracing system is required.

3.2 Insulation

3.2.1 Heat insulation should be applied to instruments and impulse lines meeting one of the following conditions:

1 Instrument detecting systems for hot fluids;

2 Cases where the normal operation of instruments and lines can be ensured by heat insulation;

3 Steam lines or hot water lines for tracing, condensate return lines, electrical heat-tracing cables and similar applications.

3.2.2 Cold insulation should be applied to instruments and impulse lines meeting one of the following conditions:

1 To prevent or reduce the temperature rise of cold media and refrigerant-carrying media during instrument detection;

2 To prevent condensation on the outer surface of instrument equipment or lines at ambient temperature;

3 Measuring lines connecting cold-insulated equipment and instruments.

3.3 Design temperature for tracing and insulation

3.3.1 The design temperature for tracing and insulation shall keep the process medium from freezing, condensing, crystallizing or precipitating in the instrument measuring lines and in the instruments.

3.3.2 The maintain temperature for water media should be above 20°C, and the temperature inside a heat insulation box should be 5°C – 20°C.

3.4 Heavy tracing and light tracing for hot water and steam

3.4.1 Tracing methods may be divided into heavy tracing and light tracing. Where the measured medium is liable to freeze, condense, crystallize or precipitate, the instrument measuring line shall use heavy tracing; where heavy tracing would cause vaporization or easy decomposition of the measured medium, light tracing or insulation shall be used. The corresponding tracing form shall be determined according to Figure 3.4.1 on the basis of the characteristics of the medium.

Figure 3.4.1 Tracing structure diagrams: (a) single-pipe heavy tracing; (b) multi-pipe heavy tracing; (c) single-pipe light tracing; (d) multi-pipe light tracing (callouts: tracing line; measuring line).