Weld Preheating on the Jobsite Made Easier | MillerWelds

Weld Preheating on the Jobsite Made Easier

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A new induction heating tool for jobsites allows contractors to insource preheating and bake out to reduce costs and save time.
Orange air-cooled cables for induction heating wrapped around a pipe on a jobsite
Operator places induction wrap around a pipe on a jobsite

Preheating and bake out in welding 

Many critical welding applications use preheating and bake out processes, which reduce the chance of defects and rework and help ensure necessary weld quality.

Preheating and bake out can help:

  • Reduce susceptibility to hydrogen-induced cracking
  • Slow down weld cooling rates 
  • Reduce material distortion

Jobsite welding applications across many industries, including construction, pipeline and shipbuilding, often require preheat. Any welding job that needs preheat can likely use induction technology.

However, traditional heating methods present numerous challenges that can cost operations time and money, as well as increase exposure to safety hazards. Learn how a new induction heating tool designed for jobsites allows contractors to insource weld preheating and bake out to reduce costs and meet tight project deadlines. 

Welding preheat methods for the jobsite

The preheating process involves heating the area around the weld joint or the entire part to a specified temperature before welding. This reduces the cooling rate of the finished weld. It also reduces hardness in the heat-affected zone (HAZ) — which results in a weld that is less brittle and more ductile while also driving out moisture to prevent hydrogen buildup and the potential for cracking.

Three heating methods frequently used on jobsites are induction, open flame and resistance. Each has benefits and drawbacks depending on the application.

Induction: This process uses electro-magnetic fields that generate eddy currents within the base metal, heating it internally from within. Induction accessories, such as cables or blankets, generate the magnetic fields and are placed on or near the part to provide continuous controlled and even heat wherever they are placed.

Flame: With flame heating, operators burn a fuel gas using a torch, sometimes with compressed air. They apply the flame directly to the part.

Resistance: This method uses electrically heated ceramic pads placed on the base metal. The pads transfer heat through radiant and conductive heat where they touch the part.

Miller now offers a small 8-kilowatt portable unit weighing 43 pounds — ArcReach® Heating Systems. ArcReach-enabled welding power sources, commonly on the jobsite already, power these systems.

This new induction heating system designed for welding preheat and bake out on the jobsite can deliver greater portability and flexibility so welders can do their own preheating quickly and safely. The new ArcReach Heater can help solve five common challenges related to weld preheating on the jobsite.

5 challenges of weld preheating on the jobsite

 

1. Expense

When comparing welding preheat methods, it’s important to consider the operating costs involved with each method.

Labor is a significant expense with the resistance method. The time-consuming setup can take hours per weld joint. With heating contractors, cost overruns are common. The insulation needed for each occurrence of resistance heating is considered hazardous waste and proper disposal is costly. Another consumable cost is the ceramic pads, which can break and require frequent replacement. Unexpected expenses for broken pads can increase the final billing vs. the estimated cost. Also, resistance heating power sources are heavy and inefficient, requiring large power drops on the jobsite. Every ceramic pad group requires a wire harness and thermocouple to power and control it. On some jobsites, wire harnesses are brought in by the truckload.

Flame heating also involves significant labor costs. Flame has a slow time to temperature, so it’s time-consuming to heat and reheat the part after operator breaks or shift changes. In addition, as specified in ANSI Z49.1, supervisors shall assure that fire watchers are assigned and hot-work authorization procedures are followed where required. Flame heating also has the recurring costs of purchasing and handling the fuel. Fuel costs can add up because of flame heating’s inefficiency, since most of the energy from the flame heats the surrounding air rather than the part itself.

The overall heating efficiency of induction can be greater than 90% with the correct output circuit design. As a result, it delivers a strong return on investment in terms of energy costs, especially for operations that use preheat on a regular basis. And because of its fast time to temperature and easy setup process, induction also delivers labor cost savings.

2. Logistics

Contractors outsource some heating processes. Some processes are also time-consuming to set up or slow to reach proper temperatures. This can result in unproductive time for operators waiting around on a jobsite.

Resistance heating is often outsourced to a third-party contractor. This subcontracted heating may not coordinate efficiently with welding work, causing delays and missed timelines.

Because welders can use ArcReach Heating Systems, operations can easily control the schedule and timing of jobsite preheating. In addition, the overall heating efficiency of induction, in terms of coil efficiency, can be greater than 90%, resulting in a fast time to temperature. This allows contractors to complete more welds and meet timelines.

3: Time 

When the weld preheating process requires long setup and teardown times, it slows the entire operation down.

Setup time for resistance heating can take up to three hours per weld joint. Operators must wire each pad, and the configurations and cabling are complex. Teardown times are also lengthy. Crews must wait for the heating equipment to cool down before they can remove it and move on to the next joint.

With flame heating, the part will cool down as soon as the flame is removed — such as when operators go on break or move around the jobsite. This wastes time when a part must be reheated after a break or shift change. And while operators can do the preheat themselves, they may have to search around the jobsite for a propane bottle that has fuel in it. If there are many empty or half-empty propane bottles on a jobsite, it can be a time-consuming hassle for an operator to find one with fuel.

With ArcReach Heating Systems, operators simply attach the heating tool to the part being heated and connect the system and thermocouples; then they are ready to preheat. Setup is typically 20 minutes or less per joint. And because induction tools don’t get hot, operators can  move them immediately to the next joint without cool-down time. This delivers much faster teardown.

4. Quality

With resistance heating, occasional pad failures or outputs that are stuck on a certain temperature can cause cold or hot spots. As a result, the pads require monitoring to prevent part damage from overheating. If a heater pad over a thermocouple burns out, the other heater pads will work harder and get hotter to try and bring that thermocouple up to the proper temperature. This also results in hot and cold spots.

Uneven heating is a common problem with the flame method. The amount and concentration of heat transferred to the part depends on several factors, including the amount of fuel consumed, distance between the flame and weldment, manipulation of the flame via adjustment of the gas control, and control of heat losses to the atmosphere.

Induction offers a more even heat profile that eliminates local hot spots in the part and heats the part from the inside out — rather than forcing flame from the outside in. Uniform heating with minimal temperature variation helps ensure quality welds.

In addition, ArcReach Heating Systems allow for automatic temperature documentation — eliminating inconsistency and time involved with doing it manually. They allow up to six temperature-reading thermocouples to be attached for multiple temperature monitoring locations. The system detects a drop in temperature from a thermocouple failure. It also automatically records temperatures, which operators can easily extract by inserting a USB drive into the unit’s USB port. The system’s data application can provide heat profile charts that can be printed and saved for reporting.

5. Safety 

Resistance heating uses ceramic pads that get hot, increasing the risk of burn hazards. There are also shock hazards when ceramic beads break off the pads and connectors have exposed electrical wire and are not repaired when necessary.

Flame heating has the obvious safety risks of working around open flame and toxic gas byproducts, which increase the risks of burn injuries, fires and explosions.

Induction heating with ArcReach Heating Systems offers a safer environment due to the heating tool staying cool (only the part gets hot) and the absence of toxic fumes. Plus, jobsites can be noisy places; induction is a quiet process that doesn’t add to that noise level like flame does.

Take control of weld preheating on the jobsite 

Induction heating delivers many benefits that help operations optimize efficiency, decrease costs and reduce exposure to safety hazards compared to other methods for weld preheating.

The new ArcReach Heater provides additional portability, ease of use and flexibility for preheating needs on the jobsite — so operations can take control of the weld preheating process and save time and money. Visit www.millerwelds.com/arcreachheater to learn more. 

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