Hotfoil-EHS for All Your Pre and Post Weld Heat Treating Needs

The Importance of Pre-Weld Heating

Pre-heating and metal prep before welding a large section of pipe.

The process of pre-heating steel prior to welding is important to understand. In general, there are two primary reasons to heat treat prior to welding.

First, it increases the temperature of the target material, resulting in a controlled (slower) cooling rate of the target material, as well as that of the weld. Thicker areas of steel, typically 1/2 inch or greater, and high-strength low-alloy steels (HSLA) are prone to the formation of weakened crystalline microstructures if the weld cools too quickly. These weakened crystalline microstructures are called martensite.  Martensite is a steel crystalline structure critical to the steel's hardness and strength; too much martensite leaves steel brittle; too little leaves it soft.

When welding, martensite can form in the newly deposited weld metal, the base target material, or
the HAZ (heat-affected zone). Applying the proper amount of pre-heat prior to welding will assist in preventing the formation of martensite. Pre-heat temperatures and soak times are dependent on the target materials type, thickness, grade, and carbon equivalency. There is ample temperature and time pre-heat information available on the Internet and from industry associations, and one should refer to this information prior to welding.

Ceramic mat heaters used to pre-heat pipe spool piece.

Second, preheating also results in the elimination of condensation (moisture) prior to the welding procedure. The presences of moisture is problematic because the water will change phase (from liquid to gas) during welding. This phase change can releases trace amounts of hydrogen, and lingering hydrogen can be absorbed into the weld. When hydrogen molecules are trapped in the newly welded metal, they affect the metals grain boundaries and impose a risk of higher weld failure. As a result, removing moisture before welding is strongly recommended.

Uniformly preheating the target material prior to welding, and then insulating the target area after welding, provides an adequate cooling rate allowing hydrogen to diffuse out of the weld joint, preventing hydrogen cracking.

For more information about the equipment and processes required for weld pre-heating, contact Hotfoil-EHS, a world leading manufacturer of heat treatment equipment. They can be reached by calling 609-588-0900 or visit their web site at https://hotfoilehs.com.

Custom Generator Trucks for Mobile Heat Treating

Hotfoil-EHS designs and manufactures custom Generator Trucks for remote heat treating applications. These truck-based, mobile heat treating systems are also know as Mobile Heat Treating Rigs.

Hotfoil-EHS will custom build a generator truck to your specification, with everything you need for a mobile, in-the-field heat treating system. Custom designs include a variety of generator sizes, power consoles, interior workspaces and layouts, air conditioning, and easy access to all electrical components. 

For more information, visit https://www.hotfoilehs.com or call 609.588.0900.

A Better Choice in Heat Treatment Control Systems

Ice Star, a Finnish company, engineers and manufactures heat treatment controllers for electric and gas furnaces, as well as for induction and resistive heating consoles. The company manufactures the most advanced metal heat treatment control system available today. Since 1984, they have been laser-focused on the development and advancement of industrial heat treatment controllers and software.

ICE Star
Model ISG
Heat Treatment Controller

Ice Star’s founder, Esa Santala, has decades of knowledge and experience in the heat treatment industry. He developed one of the first processor controlled multi-channel controllers and has since been building even more innovative products.

Ice Star controllers do not require a separate recorder. Ice Star controllers monitor all critical heat treatment variables - temperature, time, soak, upsets, diagrams, events, alarms etc. - and then provide extremely detailed records for each. Additionally, with ISPort software, you can monitor and control the heating processes directly from remote process displays and computers.

For more information about Ice Star in North America, visit Hotfoil-EHS or call 609.588.0900.

Weld Heat Treatment is Critical to Structure Integrity

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.

Welding Preheat Basics

Why preheat welds?

Weld preheating is the process of heating the base metal (parts to be welded) to a specific temperature prior to welding. The specific temperature to which the part needs to be heated (before welding) is referred to as the “preheat temperature”.

The area requiring preheat may be the whole (entire) part, or just the area immediately surrounding the weld.

Preheating may continue during the actual welding process, but many times the energy generated from welding will be sufficient to maintain the desired temperature.  The temperature of the weld between the first pass and the last pass is referred to as “interpass temperature”. As long as it can be assured that interpass temperature will not fall below the preheat temperature, continued preheating is usually not required.

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.

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.

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.

Determining whether or not preheating is required should not be taken lightly, as it is critical to the quality of a weld and therefore critical to the performance of a structure. When in doubt, review of industry code or contacting an industry expert, is imperative.

Automatic Heat Treatment Power Consoles

Typical Power Console
(courtesy of HotfoilEHS)

Automatic heat treatment power consoles are used to control various heat treatment processes (i.e. pre-weld, post-weld) by closely controlling the temperature of the item being welded. The power console accurately controls the ramping rate (up and down), the soak temperature, the set point and the time. Power consoles are available from 2 to 24 zones of control. Zone can be used either in the fully automatic or manual mode.

Ceramic Mat Heater

The power console is used to provide power to electric heating elements called ceramic mat heaters. Ceramic mat heaters are constructed of nichrome wire interwoven into ceramic beads which provides electrical insulation and protection. These heaters are quite rugged and conform to curved and irregular shapes.

Thermocouples are used to sense the target temperature and send their signal back to some type of electronic temperature controller, recorder, or combination thereof. The sophistication of the control system can range from simple manual control to fully automatic control with large graphic displays. Recorders are frequently used to document the pre-heat, soak, and post-heat process. Welding integrity depends on precise and accurate control.

Recorder used on
welding power console.

Heat treatment power consoles are built on sturdy chassis of steel and depending on ambient conditions, stainless steel. Construction includes wheels and handles for easy relocation and many electrical components for safety and convenience (such as amp meters, indicator lights, cut-off switches, fuses, and alarms).

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
Email: dap@hotfoilehs.com