By DAVID KRINER, Quality Assurance Manager/CWI Goodhart Sons, Inc.

Edited by RICHARD MANDEL, senior editor

Goodhart Sons Inc., Lancaster, Pa., fabricates, welds and installs ductwork for industrial applications such as pollution control devices, ASME pressure vessels, commercial ovens and petrochemical work. Some of the finished pieces have weighed 322,000 lbs. and have been 182-ft. in length.

Welding at our company requires a variety of procedures for ferrous and nonferrous alloys. To ensure quality, the welding crews exercise careful control of temperatures and thermal cycles in preheat, interpass and post heat stages.

To measure these temperatures, my standard has always been the use of handheld, contact-type temperature indicating sticks with calibrated melting points, such as those made by Tempil (www.tempil.com) — essentially a go/no-go tool. When the crayonlike mark on the work piece turns liquid, the welder knows that the indicated melting point has been reached.

Sometimes specifications ask for the use of infrared (IR) temperature testing devices. I have tested several types of IR guns, and my testing confirms that they are not as accurate as the sticks. They may vary in their readings according to the infrared emissions of the specific work piece. The thickness of the steel, the angle of approach and the distance of the test device from the work piece all can affect an infrared reading, and dust, humidity and other factors also have an effect. There are no such variables when using temperature-indicating sticks.

Further, infrared guns must be calibrated. Checking IR gun readings with a calibrated voltammeter with temperature gauge, I have seen excessive variations that are unacceptable for good welding procedure or to gauge interpass temperature.

Two temperature indicator sticks usually are needed to determine the temperature range of the work piece. For example, if the welder needs a preheat temperature of 200 deg. F., a mark is made on the workpiece with a 200 degree F. stick and a second stick rated higher than the interpass temperature. Occasionally a third stick is used to monitor the range from preheat to interpass. If the lower-temperature stick melts and the higher-temperature stick does not, the range is correct.

Occasionally, my inspection team double-checks temperature indicator sticks with a voltage-amp meter, which has a temperature probe attachment. This device is calibrated once a year and has always found the sticks to be extremely accurate in comparison.