Electrical heat is a central part of modern life, one most people take for granted or don’t really think about in their day-to-day lives.
Heat trace uses electricity and insulation to maintain an ideal temperature of piping or a vessel for a specific process and is relied upon in industries from chemical manufacturing to home and building construction.
On Eastern Controls’ Process Training Unit (PTU®), we are constantly upgrading the installed equipment to newer technologies and products, so naturally, when we partnered with nVent RAYCHEM, we had to engineer a heat trace system onto it. Our PTU® is one of the best tools to demonstrate the technologies and capabilities of our manufacturing partners, so this seemed like an ideal way to show best installation practices for heat trace cabling and the capabilities nVent RAYCHEM has with remote controllers and other accessories.
Eastern Controls maintains a staff of engineers responsible for designing heat trace systems, and Eastern Controls was able to provide us a great opportunity to create a design, help install, and see the project through to completion.
Below, I’ve recapped my experience to provide insight to fellow engineers and enthusiasts alike. Your design is only as good as your installation.
Pre-Installation of Heat Trace Cabling
Precautions should be taken before the installation process begins. Hold a safety meeting with your team to confirm that all proper PPE is available and that the appropriate steps are taken to avoid potential accidents. An understanding of surroundings is a critical step; when installing anything with electricity, it’s vital to ensure all piping or vessels are not operational. Plants typically wait until a planned outage to perform this kind of work. After a detail of the area hazards are catalogued, the installation specifics can begin.
Electrical heat trace (EHT) isometrics are circuit snapshots that cover a “run”, or length, of piping, to be traced for a given EHT circuit. Reviewing the EHT isometric will give you the list of materials, such as the heat trace cable, power box and end seal, accessories, and miscellaneous components. These items can be laid out for specific EHT isometrics, per the isometric requirements. Something I’ve learned that is beneficial for installers is that it’s recommended (and makes installation more efficient) to mark every foot of heat trace spooled out for an EHT isometric.
Typical EHT isometrics include:
- Piping routing
- Piping components
- Location of the junction box and end seal kits
- Circuit Tagging
- Amount of cable per heat sink for valves, flanges, supports, etc.
- Pertinent electrical data: voltage, amperage, etc.
- Temperature data: Maintain temperature, max operating and exposure temperature, hazardous area classification and T-rating
Prior to installation, an insulation resistance test, also known as a megger test, should be conducted on the cable. nVent includes this in their instructions. The megger test pushes voltage at a very low amperage through the cable to check for any breaks in the cable’s jacketing. Breaks in the cabling could result in future system failure or even electrifying the pipe. The megger test is conducted at least five more times: before installation completion, before installing components, before installing the insulation, after installing the insulation, and prior to the startup of the circuit.
Ideally, the cable would be “paid out” (laying out the exact amount of cable needed) to the pipe by running the cable along the length of the pipe and taping it to every foot of heat trace cabling. Any extra cable must be allocated at the heat sinks (a body or material- usually a valve/flange/support- where heat is lost). The slack should be the equivalent length to the amount of cable required for the heat sink and then tied off at the other end. For example, if a valve requires three feet of cable, then the cable would be paid out and the valve would be wrapped with that amount of cable.
Once safety checks have been performed, cabling has been marked, cut, and set aside along with pipe straps, tape, and other accessories, the installation can finally begin.