Heat Trace Flashcards
What is electrical heat tracing?
The installation of electrical cables that are specifically designed to produce a certain amount of heat.
What are the four basic design approaches to electric heat trace systems>
Series fixed resistance
Parallel fixed resistance
Self-regulating variable resistance
Skin Effect
What are the two main types of cables used for a series fixed resistance system?
Mineral Insulated (MI)
Polymer insulated
Is a Series Fixed Resistance system a constant wattage system?
YES
Describe Mineral Insulated Cables
MI Cables are metal tubing that forms a sheath with one or more bare conductors.
The mineral insulation is magnesium oxide or silicon dioxide.
Sheath may be made of copper or stainless steel.
Describe Polymer insulated Cables
Operate much like MI cables
Have a resistive wire connected to a source to produce heat
Constant Wattage
The insulation is a polymer plastic instead of mineral insulation.
Can Polymer Insulated Cables be cut to length?
Yes following the manufacturer’s instructions.
Are Polymer Insulated Cables practical for short sections?
No
Can be up to 3500m long
Is a Parallel Fixed Resistance system also a constant wattage system?
Yes
How does a Parallel fixed resistance system work?
Resistive elements are parallel-connected to a voltage source
Each heating element produces a specific amount of heat independent of the total cable length.
Can Parallel fixed resistance system cables be cut to length?
Yes.
The length of the cable will affect the current being drawn from the source.
How do self-regulating variable resistance systems work?
By using a material that changes its resistance as the temperature changes.
As the pipe or vessel warms up, resistance INCREASES.
How do self-regulating polymer cables work?
When the temperature is LOW, the self-regulating polymer contracts and more resistive paths make a connection that results in HIGHER CURRENT FLOW
When the temperature is HIGH, the polymer expands and fewer of the resistive paths make a connection, so the current DECREASES
Describe Skin Effect Heat Tracing
A conductor is installed in a carbon steel (ferromagnetic) tube that is welded onto the pipe that is to be kept warm
A Special skin effect conductor is is attached to the far end of the tube
High Voltage ( 2000-5000v) is applied to the conductor.
Describe power limiting cables
Constructed like fixed parallel resistance cables
heating elements are an alloy that changes resistance with temperature
Operate much like self regulating polymer types
Used for maintenance of higher temperatures
Skin effect heat tracing is for distances of :
3km up to approximately 15km
What are the 3 main reasons to use electric heat tracing?
To prevent the freezing of liquids in a pipe or container
Melt snow and ice
Maintain a specific fluid temperature in a pipe or vessel
What are the two main types of self regulating cables?
Self regulating polymer
Power Limiting
Electronic control uses ______ ________ switching that has no moving mechanical parts.
SOLID STATE
How does a soft start work?
To prevent nuisance tripping, an electronic controller that gradually raises the voltage to the circuit is used.
Current and Voltage are proportional
What is average current control used for?
Operations where maintaining a temperature at a very specific value may be critical.
What is the best type of controller for an average current control application?
Solid State Electronic Controller
TRUE OR FALSE:
Heat tracing circuits for surface heating must not be ground fault protected?
FALSE
(Rule 62-116)
Ground Fault protection and ground fault detection are often features of:
Electronic Controllers for heat tracing
What are 2 applications of electronic control that a simple tstat cannot do properly?
Soft Start
Average current control
How are MI cables supposed to be secured?
Metal banding
How are cables that have a non-metallic covering secured?
A fibre tape.
Why does a flange or a valve require more heat tracing than a pipe?
Greater heat loss
What are some common faults with heat tracing?
Incorrect temperature settings
Incorrect temperature sensing location
Insulation breakdown
Incorrect voltage applied.
What is the process for testing insulation in heat trace?
Disconnect both ends and test full run
If it fails, move to a point in the middle and test in both directions.
Continue until you find the portion which needs to be replaced.
