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).

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

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

Use External Electric Heating Panels for Ease and Simplicity

ELP tank heater construction

When it comes to heating process tanks electrically, you have two options - immersion or externally mounted panels. Immersion heaters must penetrate the tank wall, or be placed of over-the-side in an open top tank. Both approaches add cost and/or safety considerations. Sometimes entry to the tank may not be possible at all.  A good alternative are electric heating panels.

One type of exterior heater design, the epoxy laminated panel (or ELP), is a very versatile tank heater. Possessing unique flexibility, ELP heating panels can be used in a variety of heating applications ranging from freeze protection to process heating up to 212 deg. F . These panels can be used on either vertical or horizontal tanks of metallic or non-metallic construction. They can be used in dry, wet, or corrosive environments in ordinary or approved hazardous locations.

ELP heating panels are quick and easy to install, require no special tools or skills. Heaters are usually installed by banding them to the tank with metal bands or polyester straps. Installation of several ELP heating panels takes only a few minutes.

Check out the following document for more information on the epoxy laminated panel heaters.

Epoxy Laminated Tank Heater Panels from Hotfoil EHS, Inc.

Large Scale Post Weld Heat Treating Project? Use a Custom Heat Treating Furnace

Custom PWHT furnace

As opposed to factory production, onsite production of large fabricated steel equipment could be the most cost-effective way to proceed on a large construction project. When you consider the costs of factory production, which includes complexities in permitting and approvals, logistics of materials and personnel, and most importantly transportation costs, the argument for onsite production starts to make sense.

The benefits of onsite fabrication of large vessels, heat exchangers, condensers, sections of pipe, spool pieces or any other large item are compelling.

They include:

Heated parts exiting furnace

• Elimination of costly transport of large parts, including permitting and bureaucratic issues
• Reduction of fabrication cost and time
• Reduction of inspection and approval complexity
• Close control over production 
• Fabrication under local, consistent and watchful quality control methods

Onsite manufacturing is complex, and requires localized production equipment and know-how. All aspects of the fabrication process which include engineering, material logistics, material preparation, field heating, welding, post heat weld heat treatment, and testing must be carefully considered.

With regards to post weld heat treatment (PWHT), it is advantageous to have a large enough capability to do the stress relieving in one shot with a field erected heat treating furnace. The most common approach for large part PWHT is to place the fabricated part inside the furnace and heat it to the required temperature in a single firing, as per procedure. This is the most desirable type of PWHT because all parameters in the heating, soaking and cooling can be carefully controlled.  

Large field erected PWHT furnace

PWHT furnaces can be diesel, gas, or electrically fired, and can be built to accommodate very large work-pieces. Computer controls accurately ramp the item up to temperature, assure the required soak, and then cool the parts down according to specification.

Custom furnace designs range from smaller low through-put sizes, to much larger rail-driven furnaces designed to move back and forth over the materials being heated.  These larger furnaces may include crane wheels and drive systems, or even hydraulic lifting systems that lift the entire furnace for optimal transport and placement.

Large field erected PWHT furnace with vessel entering

If you have any questions about custom PWHT furnaces, contact Hotfoil-EHS for a no obligation consultation. Hotfoil-EHS has years of experience in the engineering, design, fabrication, and commissioning of large scale post weld heat treating furnaces with many successful installations around the USA.

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

Portable Hardness Testing for Field Welding

Portable Hardness Testing Kit

Hardness testing is an easy and informative test to learn important information about material properties. For most general applications, hardness can be described as the property a material has to resist indentation. In welding, its important to measure hardness of welds for quality and material compliance.

Various methods and procedures are used to measure hardness. One method is to create a "dent" on a target material (under controlled conditions) and then carefully measure the resulting indentation. The indentation correlates directly to the hardness of the material. In very general terms, the smaller the mark, the harder the material, and the larger the indentation, the softer the material.

The Brinell Hardness Number (BHN) and Brinell testers are very popular. Brinell testing is done by pressing a perfectly spherical ball (10 mm in size) into a target material with a force of over 6600 lbs (3000kg to be exact) for a minimum of 10 seconds, and then measuring the resulting impression. After which, the size of the impression is measured by an optically scaled microscope positioned over the impression.

Laboratory Brinell testers are obviously impractical in the field, but portable, lightweight Brinell testers are available for weld hardness testing in the field. These portable testers are easily transported and simple to use.  No special training is required and in a few minutes anyone can learn to determine a Brinell Hardness Number accurately.

The accuracy of portable Brinell testers are done via NIST traceable test bars. The test bars are calibrated to a uniform hardness of ±3% of their labeled Brinell Hardness Number. Additionally, the microscopes used for measurement are capable of reading within .05 millimeters.

Typical Field Procedure

A test bar with a known BHN, and approximately the hardness of the target material to be tested, is chosen. The test bar is inserted into the Brinell test instrument and the instrument placed upon the specimen.  A steel impression ball, secured in the the head of the instrument, is in contact with both the test bar and the target material. Built-in to the test instrument is an anvil, which is then struck sharply with a hammer. Via the impression ball, the impact of the hammer, regardless of force, is transmitted equally to the test bar and to the target material, leaving marks in both. The diameters of the resulting indentations are directly related to the respective hardnesses of the test bar and the specimen.  The bar is removed from the test instrument and the microscope is positioned over the appropriate indentation.  The impression in the specimen metal is measured in the same manner and the hardness is determined.

For more information on portable Brinell Harness Test kits, contact:

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

Postweld Heat Treatment

Some welding operations require postweld heat treatment

Welding is a process of joining materials, usually metal or thermoplastic, by causing a fusion at the junction of two or more physical parts. The fusion is accomplished through the creation of specific conditions at, and adjacent to, the joint area. Welding is a heat based process, but there are other heat based processes used for joining metals. The welding process differs from lower temperature joining operations, such as soldering or brazing, that do not require melting of the base metal.

There are numerous welding methods, as well as specific procedures that are applicable to different metal alloys and intended use of the finished product. Some of these procedures involve controlled heating and/or cooling of the weld and the closely adjacent area of the parts being joined. This is generally termed heat treatment, and more specifically, preheating and postweld heat treatment.

Heat treatment, in any form, is a time consuming and costly operation. Strength, toughness, corrosion resistance, and residual stress of the joint are all impacted by the proper application of heat treatment. Many application codes and standards require specific protocols for heat treating, which is utilized to achieve a specific resulting condition in the subject material or to restore material characteristics altered by production processes such as welding.

Stress relief is a benefit and goal of postweld heat treatment. During the welding process, base materials near the weldment, deposited weld metal, and the heat affected zones exhibit different levels of metallurgical phase transformation. Various degrees of material hardening occurs, particularly in the heat affected zone adjacent to the weld metal deposit, with high stresses due to melting and solidification. Stress relief through heat treatment is accomplished by controlled heating and cooling of the affected material area to relieve a significant amount of the imposed stresses. This postweld heat treatment can reduce the hardness and increase ductility, lessening the incidence of cracking in weldments. The process generally involves maintaining the target area at a specific temperature (soaking), then executing a controlled cooling schedule.

One respected source, TWI, sums up post weld heat treatment (PWHT).....

The necessity for PWHT depends on the material and the service requirements. Other factors that influence the need for PWHT are the welding parameters and the likely mechanism of failure. In some standards, PWHT is mandatory for certain grades or thicknesses, but where there is an option, cost and potential adverse effects need to be balanced against possible benefits. The energy costs are generally significant due to the high temperatures and long times involved, but costs associated with time delays may be more important. Detrimental effects include distortion, temper embrittlement, over-softening and reheat cracking, which means that control of heating and cooling rates, holding temperature tolerances and the times at temperature are extremely important, and must be carefully controlled in order to realise the full benefit of the process.

The precise level of heat control, as well as the substantial quantity of heat, required to successfully accomplish a PWHT protocol calls for the use of special purpose equipment intended for PWHT. Hotfoil EHS is a recognized manufacturer of industrial application heating equipment and specializes in the design and manufacture of power consoles, ceramic mat heaters, and accessories for pre and post-weld heat treatment. Share your application challenges with them and work together to develop a cost effective solution.