Question:
We just rebuilt our atmosphere integral-quench furnace. As the supervisor was gassing it up today, it "belched" about 50 gallons of quench oil out of the furnace through the quench vent. This had previously happened quite a while back (several years ago). This same furnace was gassed up yesterday with no problems. The burnoff stack seems to be clear.

Do you or any of your contacts have any idea how/why this might be happening?

Answer:
When “burning in” or introducing furnace atmosphere into the quench areas of an integral-quench or pusher furnace, pockets of air may remain. These pockets can suddenly ignite, resulting in a pressure buildup on the surface of the oil. This presents the real danger of an oil “burp,” or discharge, out of the quench tank as you describe.

Even overflow pipes that discharge to containment drums may suddenly be over capacity and spill oil out into the pit area. In rare cases, the pressure buildup is so severe that oil is dumped out the front door, often igniting if a pilot has been lit or another source of ignition is present. One particularly damaging plant fire was due to a relatively small floor fire spreading into a pit area that already contained an estimated 3 to 4 inches of oil from repeated (and ignored) oil discharges from the quench tank. Extensive equipment and building damage resulted. Introducing nitrogen into the suspect areas of the quench tank can eliminate the problem from reoccurring.

Other dangerous conditions to be aware of include:
  • The presence of water in the quench oil
  • Oil drag-out
  • Load hang-ups (partially in/partially out of the oil)
  • Oil buildup in exhaust stacks
  • Inner doors open during quenching
  • Processing loads with high surface area
  • Running irregularly shaped parts
  • Oil buildup in washers and temper furnaces
  • Processing powder-metal parts
Finally, remember that (depending on the heat-treating requirements of your parts) quench oils are used over a wide range of operating variables, including temperature, agitation, viscosity, quench speed and contamination. All of these variables affect oil vaporization, oil drag-out and oil-quench characteristics. In addition, quench-oil design and basket loading are important factors. In extreme cases where the variables are not properly controlled or are allowed to change over time, what was a normal, safe quenching operation may turn into a potentially hazardous one.