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:

AFTEK-EHS Welders
2960 East State Street Ext.
Hamilton, NJ 08619
Phone # 609.588.0900
Fax # 609.588.8333
www.hotfoilehs.com
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.

Epoxy Laminated Panels for Industrial Tank Heating

epoxy laminated heater
Epoxy laminated heater for tanks
Need a way to maintain process temperature for a holding tank? Looking for something easy to install and connect? Consider an epoxy laminated electric heating panel.

These heaters use a flat foil resistive element which is laminated in a multi-layer fiberglass construction using epoxy resin. The manufacturing process is done under tightly controlled heat and pressure to assure bonding and structural integrity.  The resulting electric heater design is a semi-flexible panel that is waterproof and durable.

Epoxy laminated panel (ELPs) are a very versatile option for tank heating. ELP heating panels can be used in a variety of applications from freeze protection to process heating with exposure temperatures ranging from -40 F to +212 F. ELP heating panels can be used on either vertical or horizontal tanks with diameters of 48" and above, with either metallic or non-metallic construction. They can also be used in dry, wet, or corrosive environments, as well as for hazardous and non-hazardous areas. 

epoxy laminated heater
Installed view of epoxy laminated heater.
They are quick and easy to install and require no special tools or skills. Heaters are usually installed by banding them to the tank with metal bands or polyester straps, which takes only a matter of minutes. After installing the heating panels, adhesive aluminum tape should be applied to the edges of the heaters acting as a seal. This will prevent thermal insulation becoming trapped between the heating panels and the tank.

The heaters provide a low watt density heating profile, and along with their inherent low mass,  ELPs provide excellent thermodynamic performance. 

For more information contact:

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

Ceramic Mat Heaters for Pre & Post Weld Heat Treating

ceramic mat heater
Ceramic mat heater
for pre and post weld
heat treatment.
Flexible ceramic mat heaters (also known as flexible ceramic pads or FCPs) are designed to provide stress relief for pre and post weld heat treatments for large scale welding requirements, such as those needed for piping fabrication, boilers, pressure vessels, storage tanks, pipeline construction, and mining equipment.

It's very important to pre-heat metal to a specific temperature prior to welding. Pre-heating metals reduces stress in the finished weld,  as well as eliminates moisture and improves the metallic microstructure of the weld material.  For post weld heat treatment (PWHT), use of resistance heaters to apply carefully controlled  cool-down can significantly increase the cross-weld toughness of the heat-affected zone.

Ceramic mat heaters are manufactured using high grade nickel chrome (NiCr) 80/20 wire insulated with interlocking sintered alumina ceramic beads, providing flexibility and convenience for use on curved or flat surfaces. Their design also allows for good contact and high heat transfer. Ceramic mat heaters are intended for repeated use and have considerable mechanical strength and durability. They are capable of achieving temperatures of up to 2050°F.  and are most often are supplied with ceramic insulated leads with either Camlock or Dinse type welder terminations.

The most common voltages used are 40, 60, and 80 volts (as supplied by arc welders) but many custom voltages are available. Special sizes, heating patterns and terminations are also easily accommodated with ceramic mat heaters.

For more information, contact:
Hotfoil-EHS, Inc.
2960 East State Street Ext.
Hamilton, NJ 08619
Phone # 609.588.0900
Fax # 609.588.8333
Email: dap@hotfoilehs.com

Demand Pulse MIG Welding

Demand Pulse MIG Welder
Demand Pulse MIG Welder
(courtesy of Aftek-EHS)

Demand Pulse is possible because of the MOSFET, an extremely fast electronic switch. Using constant current DC power, a wire is fed into the arc zone. As the wire approaches the work, the voltage drops as a function of the arc length. At a pre-selected arc voltage (usually 15 volts), the MOSFET fire a pulse of current to expel the tip of the wire across the arc gap. This current is supplied by means of a parallel resistor in the main current control circuit and is generally 100 amps. Switching time is measured in nanoseconds, and the total cycle time is very short, perhaps 15 nanoseconds. An inductor is not required, nor desired, since fast switching is essential. Perfectly tuned, the pulse cycles 200 times per second or slightly less.

The arc looks and sounds like “short-arc”, but a close look will show that there is no short-circuit. The arc length is from .020” to .090”, very short compared to GMAW-P done with conventional machines. This short arc length, combined with the short duration of the pulse, and the low current required to effect transfer gives a total arc “heat” far below that of either short-circuit transfer, or conventional GMAW-P. Fusion is excellent, because the arc never goes “out”.

Below is a demo video using this technology on 18 gauge stainless steel, without any burn through.

For more information contact:

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