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Annealing and Finishing Hot & Cold Rolled Carbon, Stainless Steel and Copper Tubing

All Rights Reserved by George Heisler
Product Manager, General Furnaces

Tube annealing, regardless of the material in process, has many common factors, the most prevalent being that the finished product must be annealed.

If we could obtain a single definition of annealing for a specific material on a worldwide basis, many of the problems related to our finished products in heat treatment would be behind us. Depending on background and proximity to the finished product, one readily relates to such problems where two of more producers follow the same terminology for a different anneal. In fact, more often than not you find variations within the same company:

  • Finish anneal
  • Stress relief anneal
  • In-process anneal
  • Arrested anneal
  • Spherodize anneal

These are but a few of the many terms that are incorrectly intermixed and when we receive an inquiry -- we often get a specified cycle that has absolutely no bearing on the anneal actually required. This happens in a country where we all like to think we speak the same language; what happens when translations are injected into the equation?

(Gulf States Tube - Rosenber, Texas - Seco/Warwick 12000 lb/hour continuous tube annealer - Carbon steel)

After over 40 years of unending explanations, we have finally concluded that in spite of the problems, we as an industry, have made tremendous strides in the advancement of tube processing including "annealing", so we will leave the subject of semantics and move on to the process made in producing tubing of the highest quality for every potential application. Progress, ingenious innovations and improved techniques are being displayed on a worldwide front in both the ferrous and nonferrous tubing fields. The continued growth of the various Tube Associations has exposed many advances being made in the tube industry. As SECO/WARWICK ?s field of expertise is in the heat treatment of metals, we will confine our comments to this area.

Forty-odd years ago annealing was considered a black art and to some extent a number of people think that it still is. For a fact it was, in most installations, a hit-and-miss affair looked on by management as a necessary evil they would one day try to eliminate.

(Plymouth Tube - Winamac, Indiana - Seco/Warwick 4000 lb/hour continuous tube annealer - Stainless steel)

For those ultimately responsible for the finished product, a different attitude existed. Through change and innovations over the years, we saw progress slowly making its way to the point where consistent quality tubing tailored to a specific need is now available on demand. If you have more than a passing interest in the process of producing tubing in any way, you can see the advancements made in every step of the process from the initial metal melt to the final finished anneal.

Not all of our forward movement resulted from a desire for a higher quality product. Some is the end result of the mandated need to improve our environment and others by the enforcement of so-called liability laws (this is especially true in the United States). A simple tube failure - once considered an unfortunate accident, can, under a certain set of conditions, jeopardize the economic health of an entire corporation. Disregarding the cause, the potential for financial disaster has reinforced management's attention on the need for and the importance of a properly heat treated end product. The result has been to move the heat treating operations to a level at least equal to that of the machines that produce the tubing initially. Over the last 20 years, Seco/Warwick and its predecessor Sunbeam have designed and built continuous furnaces for annealing both in-process and finished tubes in ferrous, nonferrous, and stainless steel materials (See figures, 1,2,3 and 4). The design difference as well as the process parameters do vary over a wide range, but still have considerable commonality as well as similar problems . Our latest solution to the long list of successful lines is now on line at LTV Steel in Marion, OH. LTV has installed a new roller hearth furnace system to anneal 10,000 pounds per hour of tubing. This system was commissioned for a new mill in Marion, OH for the production of welded steel tubing. The system will maintain a ?bright? finish on tubing up to 3-1/2? in diameter. SECO/WARWICK has developed a high capacity rich direct chill exogas generator to achieve optimum process results.

Our latest installments have more computer-controlled parameters than any prior annealers we have designed. The computer relates a wide range of variables and provides a constant feedback for instant recall and downloading of data to a centralized computer system. A furnace system is pictured in figures S1/S6. Temperature, tube wall gauge, conveyor speed, loading and atmosphere conditions are but a few of the parameters that can be monitored, controlled, recorded, stored, and varied by the operator with the push of a button.

The control system uses a PLC and is on the leading edge of controls regardless of the particular process. A single Allen-Bradley PLC using Wonderware* InTouchTM software (or equivalent), located adjacent to the furnace, allows the operator to have fingertip control of all of the inputs and furnace operations.

The Wonderware* software package, programmed by SECO/WARWICK, is custom tailored to exclusive requirements as specified by the end user. All the conveniences of a digital display panel are combined into a single computer terminal screen with recording and retrieval capabilities available on demand.

If utilized to the full capacity of the system, the input of a customer order code number is all that is needed to implement a specified per-programmed cycle for heat treating the entire lot of tubing.

(Wolverine Tube - Huntsville, Alabama - Seco/warvick 5000 lb/hour continuous level wound tube annealer - Copper)

Success in any process is often dependent on stabilized repeatability and, in the SECO/WARWICK systems this is an inherent characteristic. The customer order code number input to the operator interface, will determine production rates based on tube gauge, material and diameter to pre-programmed parameters. For each heat treating application, the system has a range of multiple production rates geared to the tube gauge and tube diameter.

Change is vital in a competitive world. When comparing the furnace line built only a few years ago to lines installed in the mid 90's, in addition to the obvious control function changes you see in a mature industry, change is not the norm. Yet, change is evident to the experienced eye. The atmosphere system can be generated gas, CH4, propane, or a nitrogen/methanol mix from a PSA system with a mixing station. A wide range of gas mixtures are available to the operator and the furnace process.

The range of reducing or oxidizing atmosphere is almost infinite. Coupled with the dewpoint controls and a well designed furnace, the system has the ability to produce deep blue surfaces to clean anneal or bright-finish, all simply by utilizing pre-programming and calling these conditions into play by the push of a button.

As stated earlier, changes have been slow in coming, but change today is more vital to a healthy industry than ever before. Keeping up is even a greater challenge to industry. There was a time when if you installed cutting-edge technology you could count on a good 10-year edge on a lagging competitor. Today, a one year edge is about as long as you will be comfortable with. And if you elected to stay with what was good 20 years ago when you invest in new equipment, you may well find your industry and your markets have passed you by.

(Shanghai Steel Tube - Seco/Warvick 15000 lb/hour continuous tube annealer - carbon and alloy)

Numerically controlled machines, auto feed welders, state-of-the-art controls are being used together to produce outstanding products at considerable cost savings. Yet, all too often, what happens to all of the fine work and cost savings created by this equipment? It goes into a furnace that was obsolete 30 years ago. The heat treatment is a non-uniform, hit-and-miss operation resulting in rework, excessive post cleaning and costly underutilized heat spewing into the atmosphere through flues and openings never originally designed into the unit.

By the turn of the century, no company, regardless of their present size, will be free to maintain the status quo. (The auto industry is a good example.) We often forget that one of nature's constants is change. Industry, including the manufacturers of tubing, is not immune.

Research, innovation and investments will keep our industry vigorous and growing. Change will provide the challenge and only time will decide the winners and the losers. Even with a gargantuan effort, no company can say with certainty they will obtain their goals until the year 2000. But most prefer the odds in favor of trying to the certainty of failure ahead for those that fail to do so!

*Wonderware is the registered trademark of the Wonderware Corporation For more information, please contact :

Meadville, PA, USA
Tel: 814/332-8400
Fax: 814/724-1407
Contact. George Heisler, Product Manager, General Furnaces

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