Heat Tracing of Long Pipelines - Part One

Pipelines provide a simple means of transporting materials, liquids, powders, and gasses over sometimes relatively long distances, both efficiently and inexpensively. When thermal insulation alone is not sufficient, then the pipeline needs heating.

There are two factors necessitating heating:
  1. Heat loss compensation – to maintain the pipe at a specific temperature. 
  2. Temperature raising – to elevate the temperature of the pipe and contents in a specific time. 
Materials are heated for many reasons:
  1. To prevent liquids changing state 
  2. To reduce viscosity 
  3. To heat materials in preparation for the next process 
  4. To prevent corrosion 
Electricity offers many advantages. It is clean, easy to install (or repair, if necessary), easy temperature controlled and readily available. Operating costs are low, and on a properly designed and installed system, maintenance is virtually non-existent.

Typically, two types of external heat tracing systems are being used:
  1. Mineral insulated heating cable 
  2. Heating tape 
Heating Cables – Usually of the mineral insulated (mi) type, with a variety of covering. The covering or outer sheath is of metal, i.e. copper, stainless, inconel, cupro nickel, etc. The conductors are usually of low resistance nature. The cables only give point contact, and heat transfer rate and efficiency is low. Vibration is a problem and causes insulant migration. The cables have to operate at higher temperatures to give the needed heat transfer. Heat transfer cement is usually used to assist in heat transfer. M.I. cables are semi-rigid and, once bent into shape or configuration, it is virtually impossible to get the cables straight again. Repeated bending of metal sheathed cable can set up stresses, resulting in stress cracking of the metal sheath.

Heating Tapes – these are the most versatile form of heating. They can be designed for practically any voltage, can be made for single or three phase operation, can be covered with a variety of sheaths for compatibility with the environment, etc. Heating tapes are flexible and thus easy to work with. They can be braided with either stainless steel or nickel plated copper, for hazardous environments or non-metallic pipes.

Usage of copper conductors, or other low resistance metals, is needed for running long lengths of circuits. The length of circuit is governed by temperature of the pipe, voltage supply, type and thickness of thermal insulation, amount of load given out by the tape or heat needed on the pipe, delta ‘t’, etc. Low resistance metals mean that long circuit lengths can be achieved. Long circuits are what is needed to have the voltage supply at one end only. If possible.
Various methods of heating long pipelines by heating tapes are available. It can take the form of one (1) three phase heating tape or three (3) single phase tapes.

Design Consideration
Each pipeline is different and it is doubtful if two projects will ever be the same. Factors governing the designs are:
  1. Temperature Range. This is the final designed maintenance temperature of the pipe. Thought must be given in the initial design to the materials that could be in the pipe during its lifetime. For example, an initial approach may be to pump light oil at a higher maintain temperature. 
  2. Ambient Temperature. Designs must take into account the lowest anticipated ambient temperature. 
  3. Temperature Raising. The design may ask for the temperature of the material to be raised during transit through the pipe. Alternatively, designs may request that the heaters have to have sufficient power to “melt out” a system in the event of prolonged shutdown. The specific heat and gravity of the material needs to be known. 
  4. Voltage. The most convenient voltage supply for the system. 
  5. Needed Info. Length, diameter, thickness and material of the pipeline to be heated. 
  6. Temperature Control. How the pipe is to be temperature controlled and by what means. 
  7. Corrosion Effect. Of materials near to the pipe and heater. 
  8. Materials in the Pipe. If they have a flashpoint, freezing and boiling points. 
  9. Thermal Insulation. Type, thickness, K factor, etc.
The thermal insulation on any project must be known, as this dictates the amount of heat losses and is a most important factor to bear in mind. There are various types:

Polyurethane. Usually used for low temperature applications. It is approximately 95% air and is a good insulator. It is either preformed or can be sprayed on.

Fiberglass. In preformed, half round pipe sections is a common means of thermal insulation.

Mineral Wool. This has similar properties as fiberglass. 

NOTE: In the majority of cases, heat loss tables from heater manufacturers suppliers are based on glass fiber or mineral wool.

Calcium Silicate. Widely used in plants due to its robust, solid qualities. It is not a good insulator and standard heat loss tables have to be raised by 35-40% to accommodate the inefficiency.

With using polyurethane and/or calcium silicate, care must be taken, as they are “hard” materials and do not readily flex. On steam traced lines, either a groove is cut in the insulation to accommodate the tracer, or oversized insulation is used. With mineral wool or fiberglass, it is usually sufficiently flexible to absorb the tracer if the tracer is of small diameter. This factor also has to be borne in mind with a heating cable system. Heating tapes are usually thin in nature and a grooved or oversize insulation is not needed.
To be continued in next post.

Prevent Flash Freezing in Hygroscopic Aggregate, Mined or Quarried Materials with FRP Heaters

FRP heater for freeze prevention
FRP heaters installed
(click for larger view)
When aggregate material with trace amounts of absorbed water comes into contact with very cold metal surfaces, the aggregate can instantaneously freeze, a phenomena know as “flash freezing”. When wet or frozen material encounters steel chutes or hoppers at sub-freezing temperatures, an instantaneous bond is formed. This bond causes immediate and often catastrophic blockage of the hopper and chutes. The bond and resultant blockage can be severe enough to require pneumatic drilling equipment to free up the system. Generally, this a problem for manufacturing and processing plants who utilize conveyors, chutes, and hoppers, such as coal mines, quarries, cement manufacturers, mining facilities, and power plants. Coal, sand, cement, ores, and mined products require a materials handling system that takes into consideration very cold weather and a strategy to prevent flash freezing.

FRP heater for freeze prevention
FRP heaters installed
(click for larger view)
An excellent solution to this problem are electric FRP heating panels, a waterproof, dust tight, and vibration resistant heater. FRP heaters are designed to be used in the rugged landscapes where they are required and are very strong and corrosion resistant. They are available with FM approval for use in hazardous areas and are easily customized to conform in shapes and size to virtually and chute or hopper. Furthermore, they are lightweight, can be applied to flat or curved surfaces, and are very easy to install and maintain.

Flash Freeze Animation

Welding Application Note: Demand Pulse Technology Saves Three Weeks Production Time

Demand Pulse technology
welder (courtesy of Aftek EHS)
Demand Pulse is a unique, patented welding process. Because of the low peak current, open butt pipe welds are easier in all positions.

Short arc and pulsed spray both have peak currents in the 375+ amp range, and are at peak many times longer than the Demand Pulse process.

With Demand Pulse, welding current and volts are similar to those seen when “short-arc” welding, but there are NO short-circuits - the arc never goes out, and cold laps are almost impossible.

Demand Pulse allows for the use of very light torches, and still experience extremely long tip life. A 140 amp hand torch will not overheat running 200 amps on overlay work. Its even been reported that some customers only use one tip per week with Demand Pulse,  as opposed to several per day using conventional welders.

The first two pictures below are of an initial job done by a new customer using Demand Pulse MIG. The large skids pictured have (580) open butt, 316 SS pipe welds. The smaller manifold shown has (24) welds, for a grand total of (604) welds.

Only two qualified welders worked on this demanding job. They tested other types of equipment, all with unsatisfactory results. Then, after testing a Demand Pulse system, a good coupon was produced on just the second try, so the customer purchased a system and production started immediately upon delivery.

Astoundingly, the job was completed three weeks ahead of schedule, saving the fabricator 1600 hours of production. Most importantly, there wasn't a single repair required, and all welds passed 100% X-ray to ASME Code.

Large skids with 580 welds, all open butt 316 pipe.

Small manifold with 24 welds.

After experiencing Demand Pulse, this customer commented he'll never use anything else and that the welder paid for itself on the first job.

Below are close-ups of two of the welds on the large skid. The customer insisted on TIG wash on the cap. The TIG cap had 7 repairs - welds using Demand Pulse needed NO repairs.

TIG welds need 7 repairs.

Demand Pulse required 0 repairs.

For more information, contact:

2960 East State Street Ext.
Hamilton, NJ 08619
Phone # 609.588.0900
Fax # 609.588.8333
Email: dap@hotfoilehs.com

Check Out North America's Largest Metal Forming, Fabricating, Welding and Finishing Event

Come visit HotfoilEHS at FABTECH
The annual FABTECH exhibition is happening in Chicago this year on November 9th through 12th, 2015.

FABTECH is sponsored by the the Fabricators & Manufacturers Association (FMA), SME, Precision Metalforming Association (PMA), Chemical Coaters Association International (CCAI), and the American Welding Society (AWS).  There will be 1500 companies exhibiting all kinds of forming & fabricating, tube & pipe, metalform, welding, thermal spray, and finishing equipment.

HotfoilEHS is proud to be exhibiting their power consoles, ceramic mat heaters, welders, GRID systems, transformers and power supplies again this year at Booth N27044.

It's a great event where you can see the latest industry products and developments, and find the tools to  improve productivity, increase profits and discover new solutions to all of your metal forming, fabricating, welding and finishing needs.

For more information on FABTECH, visit http://www.fabtechexpo.com.