Some design parameter should be considered before starting design heat tracing. Is the process maintenance or freeze protection?
What is the design temperature maintains, start up, worst case temperature, process operating, minimum and maximum temperature? Determine the right temperature rating or auto-ignition temperature of equipment is very important, that is number 1 safety factor of heat tracing design process. How do we find the right T-rating? This information usually be shown from MSDS and you can ask your client for it.
Ignition Temperature Flammable gases also have a temperature where ignition will take place, even without an external ignition source such as a spark or flame. This temperature is called the ignition temperature.
I’m going to focus a little bit more with Temperature-rating.Standards associations have established the T-rating, or temperature rating, as a means of classifying electrical equipment based on the maximum temperature an exposed surface may attain.
The T-rating is identified as the “Temperature Identification Number” in the National Electrical Code (U.S.), as the “Temperature Code” in the Canadian Electrical Code, and as the “Temperature Class Number” in IEC standards.
The purpose of the T-rating is to ensure that electrical equipment does not exceed the auto-ignition temperature of flammables that might be present in a hazardous location.If specify equipment T-rating is selected and then select the appropriate T-rating from the list, the heat tracing design software simply selects a heating cable with a T-rating less than or equal to the one selected.
See the table below for T-rating designations and associated temperatures.
Division T-rating
Temperature (º C/º F)
Zone T-rating
T1
450/482
T1
T2
300/572
T2
T2A
280/536
T2
T2B
260/500
T2
T2C
230/446
T2
T2D
215/419
T2
T3
200/392
T3
T3A
180/356
T3
T3B
165/329
T3
T3C
160/320
T3
T4
135/275
T4
T4A
120/248
T4
T5
100/212
T5
T6
85/185
T6
I’ve done a lot heat trace design using Tyco or Thermon. Thermon's specialty is "heating trace"; the application of steam, fluid or electric heat to piping, tanks, instrumentation and other equipment. With some electrical engineering jobs, your client may prefer Tyco products. So let’s learn heat trace design using Tyco software (not much different to use the other software). First register and down load Tyco thermal software (free). Recommended professional software to use is Trace cal pro 2. Gather the necessary information to enter into Trace cal Pro such as pipe size and material, insulation type and thickness, maintain temperature, minimum ambient temperature, service voltage, maximum exposure temperature, and area of classification, pipe length, number of pipe supports, number and size of valve.
Example gather information Pipe size and material: 1-inch steel pipe Insulation type and thickness: 1-inch fiber glass Maintain temperature: 40º F Minimum ambient temperature 0º F Service voltage: 120V Maximum exposure temperature: 680º F Area of classification: Class 1 Division 2 Pipe length: 60ft Pipe supports: Thermally insulated Valves: 2x1’’light valves(threaded)
Looking at P&ID to find out what pipes, tanks, and instrumentation need to be heat traced. Basically input all data into traceCalc Pro. TraceCalc Pro provides design calculations such as pipe heat lost, bill of material, number of circuits, electrical loads and maximum temperatures; and automated heating cable and components; and recommendations for control and monitoring selection, and much more. It provides easy-to-use standard reports; its powerful feature to help the best heat-trace solution for any particular project. As electrical designers, we have to present our work into the drawings, so consider • Find out the actual location pipe, tanks, and instrumentation need to be heat traced ; • Path of cable from power distribution center to equipments; • Grouping cable together; • Recommended laying out field junction boxes, it will easier for field wiring; • Determining the cable size, and determining circuit breaker size. Making sure the total load doesn’t exceed circuit breaker size and must use ground fault equipment protection circuit breaker type to protect against the risk of fire (NEC required,article 427-22). Also find out vendor installation instructions for pipe, valve, tanks, and vessel and so on and put those on the detail installation sheet. Hopefully this article will help new electrical designer the ideas to get started tracing design.
