(Re)Start Here — Bringing Your Vacuum Furnace Back Online After a Shutdown or Prolonged Inactivity

By Jim Grann, Ipsen Technical Director and Craig Moller, Ipsen Chief Engineer

At the start of a new year, many operators and maintenance crews return from a planned shutdown with the task of getting their heat-treating department back online as efficiently as possible. Orders are starting to come in and companies want to make sure they are ready for the demand.

The Ipsen Knowledge Center contains several articles about how to prepare furnaces for shutdown, but how can heat treaters make sure that their furnaces are ready to return to service?

Here is a list of best practices that Ipsen recommends for maintenance and operations teams to review as they return from a plant shutdown or to implement when bringing a furnace back online after being out of service for a prolonged period.

Review the Shutdown Process

What you do before your shutdown will significantly impact what happens when you go to restart your furnaces.

In this state, the furnace chamber should be clean, dry, and empty for the duration of the shutdown.

Then, as your operators are turning off each system, from pumps to water to gas, and finally powering down the furnace, they should make a note of any anomalies that may warrant maintenance attention or repair during the shutdown. Any system alarms or production anomalies should be reported as well. By addressing these issues during the shutdown, users can avoid downtime when the time comes to return to production.

If a maintenance team performs any repairs or preventive maintenance during the shutdown, those services should be documented in detail. Unexpected leaks or production issues can frequently be traced back to the last thing that was done to the furnace before the issue occurred.

Pre-Flight Checklist

Once your team has reviewed the logbook from the shutdown, it’s time to begin the start-up process, which typically begins with a series of inspections.

Vacuum Status Report

Is the vacuum pressure close to the last recorded measurement prior to shutdown? Has there been a slight increase or decrease? Is the furnace showing that it’s back at one atmosphere of pressure? Throughout a long production run, some leaks may not be evident from one cycle to the next, but a prolonged shutdown can help operators determine if there’s a slow leak that demands attention.

Is there a seal leak? Is there a gas valve leak? Was the gas system properly shut down, or left on? Knowing the answers to these questions can help narrow down your search for a mechanical leak for testing purposes.

Furnace Chamber Status Report

Once you’ve determined there are no vacuum leaks to address, opening the furnace for inspection is the next step. Oil inside the chamber may have been drawn out through the vacuum pumps if the furnace was left in a deep vacuum during shutdown. (For these purposes, a “deep vacuum” is around -30 in. pressure Hg)

Look at the bottom of the chamber and door seal. Use a flashlight to look at the space between the cold wall and the plenum. Do you see any pooling oil? If you have a deep chamber, get a clean rag and a stick and slide it towards the back of that space, then retrieve the rag and inspect it for oil.

Then inspect your pumping system valves to see where any discovered leaks may have originated and replace any seals or damaged parts. Check any pipes between the valve and the vacuum chamber on an external quench furnace for oil residue that needs cleaning as well.

If you discover oil within your chamber, do a thorough clean-up of any oil you found. Residual oil left within the chamber during a production cycle can lead to oil getting into the gas cooling heat exchanger, leaving a sticky residue that attracts dirt and debris, and could cause damage to parts and to your furnace, and affect heat exchanger performance.

Inspecting the Heating Elements

While it’s best practice to inspect the heating elements prior to shutting down the system for a prolonged period, this is another important opportunity to check the heating elements one more time before returning the furnace to service.

Once the furnace is open, look for shorts or damage within the hot zone. Break out the multimeter and check to make sure there are no shorts-to-ground happening on any of your power feed loops. Refer to your user manual to identify which elements are on each loop, then using your multimeter, check the resistance of each loop to a known ground. New furnaces will typically show resistance between 95 and 105 ohms, while readings at 30 ohms or lower tend to indicate more attention is warranted.

If you’re operating a graphite hot zone, look for dark, sooty areas that might indicate arcing. Check to see if there are any loose sections that need to be tightened or repaired. If you see any broken elements, now’s the time to replace them. While you’re there, look also at the ceramic insulators and nozzles to see if any of them require attention as well. This inspection is also a great time to install a new control thermocouple or load thermocouple jack panel if it’s been more than a year since you last replaced it.

Checking the Oil

Once the furnace chamber inspection shows that the chamber is clean, dry, empty, and any hot zone issues have been repaired, it’s time to close the door again and check the oil in the pumps. Look on the ground next to the pumps to see if there are any obvious oil leaks. Check any recent maintenance logs to see if work was done on the pumps. If there was a spill during a recent service and oil change, the maintenance crew responsible for the change should record it in the logs and any cleanup remediation they performed. Otherwise, any signs of leaks may indicate a need to replace seals.

Are the oil reservoirs full to the fill line? Is the color of the oil good? Have you inspected any recent maintenance or service on the pumps to make sure they’re ready to return to service?

Operators can move on once any concerns or issues are addressed, the oil is topped off or changed, and the system passes this inspection.

While you’re inspecting the pumps, pull the covers off any belt-driven systems and make sure the belt can slide by manually rotating the belt both directions. Make sure to break any seal that might be causing the belts to stick to the shaft. Visually inspect the belt tensioner and the condition of the belt and replace any belt, pulley, or arm that shows excessive wear. Do this only after the machine has been properly locked out/tagged out.

Turning on the Water Works

The temperature of your water system at startup will depend largely on the type of system you have, your geographic proximity to freezing winter temperatures, and the preparation work done prior to the shutdown.

If your shutdown plan included winterizing your water system and/or your factory temperatures remained consistently within standard room temperature ranges (59° to 77°F/15° to 25°C) during the shutdown, this step may be trivial. On the other hand, if your water system experienced more severe temperatures, doing a visual inspection of the pipes once the system is turned on is recommended to avoid future problems.

Establish that the water is flowing through the circuits. Make sure the pressure and flow switches are functioning. Look for visual indicators that threaded connectors don’t require tightening. Check the flow rate to see if there has been any indication of bottlenecks that might have been caused by corrosion within the pipes. Inspect the run for any newly formed leaks. If an outdoor evaporation tower is being used, check to see that there is no snow or ice buildup (or other natural occurrence) affecting its function.

Gassing Up

If the inert gas valve to the furnace has been closed, this is a good opportunity to look for leaks. First check any gas fittings, connections, or valves where the gas pressure may have been building up for leaks. For positive pressure leak detection, use a bubble solution or soapy water on all positive pressure joints of the piping. Inspect for growing bubbles that indicate gas escaping through a leak. Make a point to check any threaded connections to see if they need to be tightened — these are frequent culprits of system leaks. Check the long piping that runs back to the storage tank for signs of leaks at any splits, unions, turns, or joints.

Once the inspection has been completed and any leaks have been fixed, it’s time to turn on the inert gas to the furnace. Once the gas pressure has been restored, inspect each of the connectors to the furnace from the gas source to the exterior of the chamber with the same scrutiny.

Some gas systems issues may need to be serviced by your local gas provider. Review your contract with your provider and consult with them if an issue that you discover falls within your service agreement.

Power Up

With the inspection of each of these elements complete, the operator should power up the control cabinet. Review and clear any of the active alarms that pop up — many of them may be related to the process of shutting down the furnace. Typically, users may encounter water or gas alarms which should clear up once all systems are back online.

Check to see if the furnace is reporting that it’s in a ready state. Once the condition is clear, warm up both the roughing pump and the diffusion pump by running them for about an hour, holding the diffusion pump at around 200 microns of pressure or less.

With the pumps warmed up, check to see if the diffusion pump has been able to hold at 200 microns. If the pressure inside the diffusion pump has increased by 100 microns or more, it may be signs of a leak, outgassing, or dirty oil. Further inspection is recommended.

However, as long as the diffusion pump vacuum remains at or below that 200-micron threshold, the furnace should be ready to return to operations.

Users might be tempted only to warm up the diffusion pump and to leave the noisy roughing pump off, but it’s important to have both pumps operating optimally before they’re asked to perform in production. A failure to do so might result in moisture getting into the roughing pump’s oil system, leading to unwanted oil emulsification.

The Burnout

Some customers will perform a burnout cycle before returning the furnace to production. One typical burnout cycle would instruct the furnace to ramp up to 2100 °F under partial pressure for an hour, then full vacuum for another hour, followed by a fan quench or overnight vacuum cool down. It’s another opportunity to check leak rates and make sure the contents of the vacuum remain clean, dry, and empty under vacuum.

As with many burnout cycles, this can keep your furnace out of production for 12 to 24 hours if it’s required. However, it may not be necessary to do a burnout if the furnace has been operating reliably — frequently a cold leak rate or a maintenance leak test can suffice.

Check your furnace’s maintenance history and review any guidelines for best practices from your customers to see if a burnout is necessary to meet the customers’ requirements.

Back to Work

While following good maintenance practices prior to shutdown will make your start up process much easier, following a good start up protocol can help you ensure you can get your furnaces back into production without unexpected, preventable issues.

If you do run into any issues that you can’t seem to resolve, contact Ipsen Customer Service by calling 1-844-GO-IPSEN or emailing us at Technical@IpsenUSA.com.