Hotfoil-EHS Power Consoles: Eurotherm Master Controller Set-up for PWHT Procedure

This video explains how to set up the Eurotherm Temperature Controller on a Hotfoil-EHS Power Console in a Primary/Secondary relationship.

Understanding heating rate, soaking temperature, soaking time and cooling rate for PWHT (Post Weld Heat Treatment)

Post-weld heat treatment (PWHT) is a crucial step in the welding process, as it helps to mitigate the adverse effects of welding on the microstructure and mechanical properties of the welded components. The main objectives of PWHT are to reduce residual stresses, improve ductility, reduce the risk of stress corrosion cracking, and temper or soften the heat-affected zone (HAZ). The four key factors that influence the effectiveness of PWHT are heating rate, soaking temperature, soaking time, and cooling rate.

1. Heating rate: The heating rate refers to the rate at which the temperature of the welded component increases to reach the desired soaking temperature. A controlled and uniform heating rate is essential to avoid the formation of undesirable temperature gradients within the material, which can lead to distortion and cracking. A slow, steady heating rate also ensures that the material undergoes sufficient thermal stress relief, reducing residual stresses and improving the mechanical properties.
2. Soaking temperature: The soaking temperature is the target temperature at which the material stays during the heat treatment. The selection of an appropriate soaking temperature is vital, as it determines the extent of stress relief, the softening of the HAZ, and the overall improvement of mechanical properties. The soaking temperature is carefully chosen based on the material's composition, prior heat treatment, and the desired outcomes of the PWHT. Too high a temperature may cause grain coarsening and reduce the material's strength, while too low a temperature may not provide adequate stress relief or soften.
3. Soaking time refers to the duration the material holds at the soaking temperature. The soaking time is critical for allowing sufficient time for the microstructural changes to occur, such as diffusion of hydrogen, precipitation of carbides, or tempering of martensite. Proper soaking time reduces residual stresses and improves ductility and the desired microstructural changes. Insufficient soaking time can lead to incomplete stress relief, while excessive soaking time may result in grain coarsening, which can adversely affect the material's mechanical properties.
4. Cooling rate: The cooling rate is the rate at which the temperature of the material reduces after the completion of the soaking phase. The cooling rate significantly influences the material's final microstructure and mechanical properties. Controlled and uniform cooling is essential to prevent thermal gradients that could cause distortion or cracking. Different cooling rates may be required depending on the material and the desired outcome. Faster cooling may achieve a harder, more robust microstructure, while slower cooling rates can produce a more ductile, softer material.

In summary, the heating rate, soaking temperature, soaking time, and cooling rate are essential parameters requiring careful controlling during post-weld heat treatment. These factors determine the effectiveness of the heat treatment process in reducing residual stresses, improving ductility, reducing the risk of stress corrosion cracking, and achieving the desired microstructure and mechanical properties in the welded components.

Pre and Post Weld Heat Treatment

Heat treatment in any large-scale welding process (such as pipeline welding, shipbuilding, boiler manufacturing) is critical to a weld's efficiency and, therefore, essential in a structure's performance, and therefore its importance can never be overlooked. 

An examination of industrial code or a consultation with a welding specialist is imperative if in doubt. A review of the welding code is the first determinant of whether preheating is required. The welding code carefully defines the minimum preheat, the temperature, the soak time, and the welding method. Many requirements, all obtained from years of rigorously checked data, are recognized by welding codes. This data is well supported by several sources, including metallurgical research, chemical material properties, and radiographic analysis. 

Welding heat treatment in its simplest form is the process of heating the base metal (parts to being welded) before welding to the desired temperature and then allowing it to cool at a given rate under regulated conditions. The exact temperature the component needs to achieve (before welding) is called the "preheat temperature." 

There are several main reasons why preheating before welding is necessary. A preheated part cools more slowly, which slows down the welded part's overall cooling rate. This slow cooling strengthens the metallurgy (crystalline structure), which makes it less susceptible to cracking. Hydrogen that could be present immediately after a weld is therefore released more effectively, reducing cracking risk. Preheating at the weld joint and surrounding metal often mitigates stress from the shrinkage. It is preheating that decreases the risk of fractures due to brittleness during processing. 

Electric preheaters for welding, known as "ceramic mat heaters," are durable and versatile heating components built to fit evenly around the weld and surrounding area. Ceramic mat heaters are temperature controlled by a power console that uses thermocouples and electronic controllers to regulate the preheat temperature profile, track it, and record the temperature data. 

Another less favored method for heating the target piece is with a torch or open flame, but this method has apparent safety issues and controllability problems. Also used are heat treat furnaces, but these usually involve off-site transport of the target item. 

For safety, portability, and controllability, induction heaters give an appealing alternative. Induction heating is endorsed because, instead of open flames or external electrical components, it uses molecular excitation as its source of heat. Induction heating operates very rapidly, and there are far fewer worries about component contamination since there is no interaction with the target item. When very high temperatures and uniform control is required, many industrial processes use induction heating.

It is critically important to review and discuss your heat treating requirements with an expert before welding. Don't risk safety or waste time and money by "winging it" when it comes to heat treatment.

Hotfoil-EHS
609-588-0900
www.hotfoilehs.com

Hotfoil-EHS Manufacturing and Distribution Facilities

Hotfoil-EHS, Inc. is an organization with over 70 employees and an impressive engineering capability. Through continued re-investment of profits, Hotfoil-EHS acquired additional large fabrication facilities and today is a full-service engineering, design, and manufacturing company of industrial heating equipment. Their Hamilton, NJ headquarters provides 68,000-square-feet of manufacturing space, with other manufacturing and distribution facilities located in Chattanooga, TN, LaPorte, TX, and Birmingham, England.

https://hotfoilehs.com

609-588-0900

The Importance of Post-weld Heat Treatment for Welding Repairs

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 treatment furnace.

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.

Custom Heat Treatment Furnaces Designed for the Most Challenging Applications

Hotfoil-EHS is a New Jersey based company who will design and fabricate custom heat treatment furnaces. From small, low-throughput furnaces, to high yield furnaces, to rail-driven furnaces designed to move back and forth over the materials being heated, Hotfoil-EHS has done it all.

From decades of experience in furnace production, many important furnace engineering discoveries were made that save time, money, and improve the end product.

Contact Hotfoil-EHS for your next heat treatment furnace requirement.

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

Welding Heat Treatment Products from Hotfoil-EHS

Here's a little shameless, self-promotion from your friends at Hotfoil-EHS.

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.

Fusion45: New Rugged Induction Heater Improves Weld Quality

New Welding Induction Heater

Heat treating isn’t done in a laboratory, or a clean room. Applications are out in the real world, where dirt, grease and grime are normal. Hotfoil’s new induction heater is designed to work in the toughest conditions, and continue to run shift after shift.

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.

Pre and post-weld heat treating (stress relieving) is a growing market for induction heating systems because it offers significant benefits such as excellent heat placement and distribution, lower cycle times, safety, ease of use, and efficiency.

Induction heating can improve your bottom line by decreasing weld failures, and decreasing setup and tear down times. The technology allows for accurate temp control, without heavy electrical service or complicated controls. The portability and ease of use will allow you to heat more welds faster.

Check out the new Hotfoil-EHS Fusion45 Induction Heater:

The Hotfoil-EHS Fusion45 Induction Heater from Hotfoil EHS, Inc.

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).

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

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.

Pre Weld and Postweld (PWHT) Heat Treatment Furnaces

Industrial furnaces are used for pre and post-weld heat treating by welders and fabricators to heat-treat weldments or metallic parts. Industries that require these types of furnaces include pressure vessels and piping, storage tanks, building construction, bridge building, offshore platforms, petrochemical plants, power plants, and oil and gas refineries.

By using furnaces for PWHT,  stress introduced by the welding process is reduced and redistributed through the heating, soaking and cooling the weldment/machined surface. This greatly improves the weld properties. PWHT is most times mandatory in order to comply with welding codes and specifications for the welding of carbon steels, stainless/high alloy steels and work hardened steels.

Fairly sophisticated control systems carefully follow mandatory heating and cooling profiles, as outlined by welding code. Control systems with thermocouples that monitor internal furnace temperature, along with weldment part temperature are usually included. These control systems also include the ability to ramp up to temperature and cool off over specified time intervals. Finally, the use of recorders or data loggers is common for quality control documentation.

Additional benefits of pre and post weld heat treating are:

• Improved ductility and/or harness
• Lower risk of brittle fracture
• Improved metallurgical structure
• Reduction in diffusible hydrogen induced cracking 

Most pre or post weld heat treating furnaces are customized in one way or another, whether it size, total BTU output, energy source (electric, gas, oil), control scheme, door configuration, or having the furnace built on wheels or on rails.

Furnaces can be designed permanently, portable, or field erected. By having the furnace local, or right on-site, companies eliminate the need to send parts out and thus save time and costs associated with shipping. Depending on the scope of work, its not uncommon for the investment made in a fabricated furnace to pay off within the first year.

For more information on any custom built pre heat or post weld heat treat furnaces, contact:

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

Ceramic Heater Pads for Weld Preheating and Post Weld Heat Treating

Welding ceramic pad heater
(courtesy of HotfoilEHS)

The goal of preheating and post weld (PWHT) heating is to maintain temperature between weld passes and to uniformly control changes in target temperatures. By properly achieving, maintaining, and then cooling weld temperatures, you lower weld stress, distortion, reduce shrinkage stress and allow unwanted hydrogen to escape.

It is very important to understand the material characteristics of the metals being welded, and know minimum and maximum preheat temperatures, particularly in tempered steels.

For most preheating, post heat treating, and interpass heating, precise temperature control isn't required. Its more important to maintain a minimum temperature, and stay within an acceptable range during the actual welding process, as well as during cool down.

Exceptions are with tempered steels. Tempered steels have already been heat treated at the steel mill and applying too much preheat can alter that tempering. In these cases, proper set point, temperature limiting, and temperature ramp rate of the welded part is critical.

Use of Ceramic Heater Pads

Resistance heating pads are constructed of ceramic beads strung on nichrome wire. These resistance heating elements accurately raise the workpiece temperature to the proper temperature before, during, and after welding, complying with recommended preheat, interpass, and PWHT practices. These semi-flexible ceramic heater pads, with their interlocking beads and high temperature wire, allow for a fit conforming to the shape of the workpiece, and are capable of temperatures up to 1,850 degrees F. Ceramic mat (pad) heaters have an additional benefit in that they don’t have to be moved during welding.

Recorders and controls used for
welding preheat and post heat.

Electronic temperature controllers use several thermocouples spot welded to the workpiece to monitor and regulate the actual part temperature throughout the operation. Many times the electronic controllers have ramping or temperature profiling capabilities, so that heat-up and cool-down can be carefully controlled. Recorders are often used to produce a record of the temperature profiles over time before, during, and after welding. This is important when welding jobs require careful documentation.

An average application is as follows: the heater pad is wrapped around the workpiece, and insulation is applied to the weld joint and the temperature controller is set. Once preheat temperature is achieved, a welder removes the insulation and starts their work. After the weld, the ceramic heaters can be placed over the weld and the controllers can be reset for proper PWHT.

Ceramic Mat Heaters for Pre & Post Weld Heat Treating

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