Showing posts with label post weld. Show all posts
Showing posts with label post weld. Show all posts

Thursday, October 25, 2018

Hotfoil-EHS Heat Treating Power Consoles


Precise control over your pre-weld and post-weld heat treatment parameters are critical. Accurate temperature control, specific soak times, uniformity, and controlled heat up and cool down times are required to ensure strong welds. Hotfoil-EHS power consoles are designed to provide the best control, easiest user interface, and longest lasting operation, even in the toughest environments. Using only the highest quality components, Hotfoil-EHS power consoles are field-tested and application proven. Control systems can be specified with or without recorders or ramping controllers, and are standardly available in 6, 9, 12, 18, and 24 zone configurations.

https://hotfoilehs.com
609-588-0900

Tuesday, September 11, 2018

Indirect Resistance Heating

weld preheat heater
Indirect resistance heating example:
Weld preheat ceramic mat heater.
With indirect resistance heating, a heating element transfers heat to the material by radiation, convection, or conduction. The element is made of a high- resistance material such as graphite, silicon carbide, or nickel chrome. Heating is usually done in a furnace, with a lining and interior that varies depending on the target material. Typical furnace linings are ceramic, brick, and fiber batting, while furnace interiors can be air, inert gas, or a vacuum.

Indirect resistance heating can also be done with an encased heater, in which the resistive element is encased in an insulator. Called metal sheath heaters this type of heater can be placed directly in liquid to be heated or close to a solid that requires heating. Numerous other types of resistance heating equipment are used throughout industry, including strip heaters, cartridge heaters, and tubular heaters.

Clamp-on pre-weld electric heater
Indirect resistance heating example: 
Clamp-on pre-weld electric heater.
Resistance heaters that rely on convection as the primary heat transfer method are primarily used for temperatures below 1,250 ̊F. Those that employ radiation are used for higher temperatures, sometimes in vacuum furnaces.

Indirect resistance furnaces are made in a variety of materials and configurations. Some are small enough to fit on a counter top, and others are as large as a freight car. This method of heating can be used in a wide range of applications. Resistance heating applications are precisely controlled, easily automated, and have low maintenance. Because resistance heating is used for so many different types of applications, there are a wide variety of fuel-based process heating systems, as well as steam-based systems, that perform the same operations. In many cases, resistance heating is chosen because of its simplicity and efficiency.

Electric hopper heater
Indirect resistance heating example: 
Electric hopper heaters.
Indirect resistance heaters are used for a variety of applications, including heating water, sintering ceramics, heat pressing fabrics, brazing and preheating metal for forging, stress relieving, and sintering. This method is also used to heat liquids, including water, paraffin, acids, and caustic solutions. Applications in the food industry are also common, including keeping oils, fats, and other food products at the proper temperature. Heating is
typically done with immersion heaters, circulation heaters, or band heaters. In the glassmaking industry, indirect resistance provides a means of temperature control. Many hybrid applications also exist, including “boosting” in fuel-fired furnaces to increase production capacity.

Resistance heating applications are precisely controlled, easily automated, and have low maintenance. Because resistance heating is used for so many different types of applications, there are a wide variety of fuel-based process heating systems, as well as steam-based systems, that perform the same operations. In many cases, resistance heating is chosen because of its simplicity and efficiency.

Contact Hotfoil-EHS for any industrial resistance heating project. With decades of application experience, Hotfoil-EHS engineers can help you design a system tailored to your exact needs.

Wednesday, May 16, 2018

The Importance of Post-weld Heat Treatment for Welding Repairs

welding
Welding is the process of melting two metals together. During the welding process, the metal is exposed to very high temperatures and undergoes a phase change, first from solid to liquid, then back to solid as it cools.

During welding, residual stresses are formed in an area referred to as "the heat affected zone" or HAZ. In the HAZ, differential contractions occur as the metal heats, liquifies and then cools to ambient.

Residual stresses have a significant impact on the performance of a weld and their reduction is highly desirable. The undesirable impact of residual stresses in welded metal structures involve fatigue performance and corrosion resistance.

heat treating furnace
Heat treatment furnace.
pwht with resistance heaters
PWHT with resistance heaters
Welding repairs are increasingly a structural integrity concern for aging  equipment such as pressure vessels, piping systems and other large steel systems. The make up of residual stresses near repair welds can be drastically different from those residual stresses of the original weld.  Post-weld heat treatment (PWHT) is used to reduce residual stress in steel and and should be used for welding repairs ( as well as on new welds).

PWHT is proven very effective in reduction of high residual stress around the weld repair. Conventional PWHT can be done by combustion furnace, induction heaters or electric resistance heaters (ceramic pad heaters). Accurate ramp and soak times, as well as data recording can be done with modern power console systems. It is strongly recommended to apply PWHT for all original and repair welds.

Wednesday, January 31, 2018

Pre Weld and Post Weld Heat Treatment

Pre Weld and Post Weld Heat Treatment
Welding between insulated heating areas
Heating done by ceramic heaters (pink). 
There are several key reasons why it's important to preheat before welding. First, a preheated part cools more slowly, which slows the overall cooling rate of the welded part. This improves the metallurgical (crystalline) structure and makes it less prone to cracking. Additionally, hydrogen that may be present immediately after a weld is also released more efficiently, which further reduces the possibility cracking. Preheating also mitigates stress from the shrinkage at the weld joint and nearby metal. Finally, pre-heating reduces the possibility of fracture during fabrication due to brittleness.

An industry standard means of accurately managing the pre-heat and post-weld heat treatment is through the use of specialized electric heaters. Electric welding preheaters, known as "ceramic mat heaters", are rugged and flexible heating elements designed so that they conform uniformly around the weld and surrounding area.  Ceramic mat heaters are normally controlled by a power console that uses thermocouples and electronic controllers to regulate, monitor, and many times record, the preheat temperature profile.

ceramic mat heaters on spool piece
Ceramic heaters on spool piece.
Welding codes, gathered from years of rigorously tested data, including metallurgical science, chemical properties of materials, and radiographic analysis, provide specific detail on the minimum preheat temperature, the soak time, and the welding process to be used.

Before deciding to preheat or post heat any welding job, consult with a heat treating expert to make sure proper welding code requirements are being followed.

Tuesday, March 28, 2017

Weld Heat Treatment is Critical to Structure Integrity

Welding pre-heat
Welding pre-heat is critical to the quality of the weld and
and the integrity of the structure.
In any large scale welding operation (such as pipeline welding, shipbuilding, boiler fabrication) heat treatment is critical to the quality of a weld, and therefore critical to the performance of a structure, and never should not be taken lightly.

When in doubt, review of industry code or a consultation with a welding expert is imperative. Welding code is the first determinant to whether pre-heating is needed. Welding code carefully specifies the minimum preheat temperature, the soak time, and the welding process. Many criteria are considered by welding codes, all gathered from years of rigorously tested data. This data is accumulated from many sources, including metallurgical science, chemical properties of materials, and radiographic analysis.

In its simplest form, weld heat treatment is the process of heating the base metal (parts to be welded) to a desired temperature prior to welding, and then allowing it to cool at a given rate under controlled conditions. The specific temperature to which the part needs to be heated (before welding) is referred to as the “preheat temperature”.

There are several key reasons why it's important to preheat before welding. 
  • A preheated part cools more slowly, which slows the overall cooling rate of the welded part. This improves the metallurgical (crystalline) structure and makes it less prone to cracking. 
  • Hydrogen that may be present immediately after a weld is also released more efficiently, which further reduces the possibility cracking. Preheating also mitigates stress from the shrinkage at the weld joint and nearby metal. 
  • Pre-heating reduces the possibility of fracture during fabrication due to brittleness.
Electric welding preheaters, known as "ceramic mat heaters", are rugged and flexible heating elements designed so that they conform uniformly around the weld and surrounding area.  Ceramic mat heaters are normally controlled by a power console that uses thermocouples and electronic controllers to regulate, monitor, and many times record, the preheat temperature profile.

Another less preferred method to heat the target piece is with a torch, or open flame, but this method carries safety concerns as well as controllability issues. Furnaces are also used, but these typically require the transport of the target piece off-site.

Induction heaters offer an attractive alternative for safety, portability and controllability. Induction heating is unique because it uses molecular excitation as its source of heat, as opposed to open flames or external electric elements. Induction heating works very quickly, and since there is no contact with the target piece, there are far less concerns about part contamination.  Many industrial processes use induction heating when very high temperatures and uniform control is desired.

Each welding application has it's own unique set of circumstances which dictate the optimal heat treating method.  It is always best to contact an expert and solicit their opinion on your best available option.

Sunday, January 22, 2017

Applying Ceramic Mat Heaters for Pre and Post Weld Heat Treatment

Designed for pre and post weld heat treating, ceramic mat heaters function efficiently for both curved and flat applications. The flexibility of these heaters provides a convenient means to heat treat large metal surfaces in the field.

The application of ceramic mat heaters is straightforward - the heater is placed directly on the part to be welded, insulation is normally laid over the heater, and voltage is applied. A thermocouple is tack-welded near to monitor the part. The part is brought up to temperature and then the welding is done. After the weld, the part is cooled at a controlled rate.

Ceramic Mat Heaters
Welding a large pipe with localized heating using
ceramic mat heaters.
Pipe prep before welidng
Preparing the pipe for the weld and allowing
the heaters to raise the temperature of the pipe.

ceramic heaters before weld
Wrapping ceramic mat heaters around
spool piece.
Close-up of ceramic mat heaters around
spool piece.

Thursday, July 14, 2016

Custom Heat Treating Power Consoles Solve Many Potential Field Problems

Weather-proof, Stainless Steel Power Console
Weather-proof, Stainless Steel
Power Console
Standard heat treating power consoles available from a variety of manufacturers pretty much cover the same set of basic welding requirements. In many field situations however, there can be unusual circumstances such as difficult locations, available power sources, and environmental concerns. In these situations custom manufactured power consoles will provide welding outcomes with fewer operational problems, higher quality output, and greater safety.

Standard power consoles are available 3, 6, 9, 12, 18, 24 and 36 zone configuration (zones are many times referred to as "way" such as 3 way console, 6 way console, 9 way console, etc.) Each zone provides a point of control. The type of control can vary depending on the requirement of the weld. Some zones only need simple on-off or proportional control. Some welding jobs require more sophisticated temperature control profiles, thus requiring tight control with temperature vs. time ramping. Additionally, these more sophisticated control requirements may also need data logging or recording for quality compliance. In many situations custom cable sets are required to deliver the heater power and thermocouples to the workpiece. A power console manufacturer should have the experience and knowledge to consult, recommend, and install whatever zone control and cabling requirements your job needs.

Power console and custom cable sets
Power console and
custom cable sets
The operating environment is another important consideration for power console customization. Standard power console cabinets are usually made from a medium gage sheet metal and painted with an industrial grade rust-resistant paint. While fine for relatively dry and non-corrosive atmospheres, these are subject to quick deterioration when moved into areas where higher than normal concentrations of salt, chlorine, or other corrosive gasses exist. In these situations, careful consideration of exposed materials needs to be applied. Perhaps an all stainless steel design is needed? Or maybe special corrosion resistant paints or epoxy resins should be specified? Or maybe you only need a special color paint? Working with a power console manufacturer who has the flexibility in their manufacturing process and experience on the floor to provide these options is preferred.

Custom painted power console
Custom painted
power console
Finally, look for a power console manufacturer who can handle unusual power system requirements. A manufacturer who can adapt their systems to unique voltages and current requirements is a big plus. Look for an equipment company that has experience and production capabilities for a wide variety of transformers - single or dual- and can even supply custom built transformers.

And of course, always try and find equipment built right here in the USA.

For more information on ANY welding power console, contact:

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


Thursday, June 30, 2016

New Video on Ceramic Mat Heaters for Welding Heat Treating

Just a short video on Hotfoil EHS pre and post weld heat treating mat heaters (also known as pad heaters).

Monday, June 13, 2016

Ceramic Pre Weld and Post Weld Heaters Get The Heat to the Weldment Efficiently

Ceramic mat heaters
Ceramic mat heaters
The most important feature of a resistance heater is the ability to transfer the heat away from the resistance wire to the outer covering where it can be absorbed by the work piece. Even when accurately controlled, a poorly designed or poorly applied heater can cause the wire temperature to exceed the wires operational limits. Ceramic mat heaters, also known as ceramic pad heaters, are designed to produce more even and efficient heat transfer while maintaining maximum flexibility.

Design:

1) Sintered alumina oxide is formed into shapes and fired at precise temperatures to produce a ceramic insulator with a combination of high dielectric strength and efficient, fast heat transfer. This ceramic is also solid enough to withstand physical shock and resistance to oxidation and corrosion from a broad range of chemicals and atmospheres.

2) An accurately measured length of stranded nickel-chromium wire is precisely wound through the ceramic beads ensuring electrical isolation to produce a compact and flexible resistance heater. Suitable for operation at 2000 deg. F.

3) The resistance wire is then metallurgically bonded to a stranded nickel-copper wire to provide trouble free electrical continuity. The flexible stranded cold junction wire is connected to brass Twistlock connectors fitted with insulated sleeves. The cold junction extension leads are rated for 250 deg. C continuous temperature.

Ceramic mat heaters are efficient, time-tested, and proven heater technology in pre-weld and post weld heating, and are designed for the harsh realities of the welding environment.

For more information, contact:

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

Thursday, January 21, 2016

HofoilEHS - Your Preferred Source for Pre and Post Weld Heat Treating

HotfoilEHS is a premier manufacturer of pre weld and post weld heat treating equipment. EHS manufactures and sells pre and post-weld heat treating equipment including power consoles, ceramic mat heaters, thermocouple attachment units, pin welders, Brinell testers, Poldi hardness testers, thermocuple wire, insulation, and accessories.

The below video is a little shameless, self promotion.



Power consoles are standardly offered in 6, 9, 12, 18, and 24 zone configurations with a variety of control and recording systems.

Twin heating modules, with and without recorders, and optional ramping controllers are available from EHS.

For special projects, EHS can provide mineral insulated (MI) heating circuits designed into a blanket-type layout, using clips to attach the circuits to a wire mesh in a configured pattern. The circuits are CSA and FM Approved for hazardous and non-hazardous areas.

EHS also offers short or long term rentals on power consoles, temperature recorders, and ceramic mat heaters along with complete support and training services.

EHS engineers, designs, and manufactures proven systems to effectively complete any project more efficiently than competitive systems, while staying within budget. Years of application experience and successful installations have produced thousands of happy customers.

Monday, September 21, 2015

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