Temperature measurements at third parties

Over the years, TRATER has acquired unparalleled experience in measuring temperatures during heat treatments in the oven. TRATER has selected the best materials depending on the temperatures, the best equipment to have signals not affected by disturbances and, thanks to more than 1500 treatments carried out every year in its 12 ovens, it has acquired great sensitivity in identifying the most critical geometries and the most difficult points to heat for each item, whether they are heat exchangers weighing hundreds of tons, or pressure vessels or welded structures.

Trater has invested in software and systems capable of managing hundreds of thermocouples positioned simultaneously in each oven, in order to immediately provide the operator with the distribution of temperatures on the items and the relative expansion of the surfaces, to avoid upsettings and plastic deformations of the components , which lead to shortenings of the life of the items due to stress corrosion cracking. TRATER uses hundreds of kilometers of thermocouples every year to guarantee correctly treated items.

It has staff 24 hours a day in charge of monitoring thermal cycles. Unattended thermal cycles are not carried out. TRATER also makes this service available to its valued customers for the monitoring of thermal cycles conducted in other companies.

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The most valid method for controlling and measuring temperature during heat treatments carried out in the oven is based on the use of thermocouples. Sheathed thermocouples are used for treatments at high temperature and/or with strong turbulence of hot gases. They are made through drawing, with the two conductors insulated in mineral oxide and the external protection sheath in inconel or AISI 310 stainless steel.

Thermocouples with fibre insulation are very practical to use and are instead made with the two conductors insulated in a temperature-resistant fibre braid. In relation to their type of insulation they can be used up to a temperature of 1200°C and have, as a peculiar characteristic, the fact that they are normally used in a disposable way. They are supplied in skeins, distinguished by manufacturing batch and easy to trace, from which the individual thermocouples are obtained, of variable length and suitable for reaching all parts of the item on which the temperature is to be measured. At the end of each treatment, the used thread is scrapped (disposable).

The two types of thermocouples indicated also differ in their mounting methods:

sheathed thermocouples require mechanical fixing using a nut and bolt, grooved and welded to the item to be treated;

Fibre insulated thermocouples are attached to the item by capacitive discharge in accordance with ASME Code VIII, Div. 1 – 2.

Trater has a very large number of sheathed thermocouples (around 300), currently calibrated, up to twenty meters long and always ready for use in the plant. It also purchases thousands of meters per month of disposable thermocouple wire, of various types for different temperatures.


Only a correct position of the thermocouples, in contact with the items, in the most critical points, will guarantee effective temperature control and the success of the treatment. Measuring the oven air alone is not sufficient and leads to inevitable failures. In general, thermocouples must be positioned on the items according to the following criteria:

on the maximum and minimum thickness

on the sides of the item

on the intermediate thicknesses

inside accessible closed chambers, when thicknesses exceed 50 mm

at the top and bottom of the item

on areas, sections, appendices and other details that may be of specific interest or geometrically differ from the rest of the item.

Other factors must be carefully evaluated to position an adequate number of thermocouples to be used to control a thermal cycle and each individual case is studied and examined in depth by our Technical Office, in relation to:

the type of treatment to be performed;

the geometric complexity, dimensions and weight of the item to be treated;

the characteristics of the oven used (type and number of burners and automatically controlled zones)

the positioning of the item inside the oven itself.

In case of the simultaneous treatment of more items with the same geometry and mass, it is possible to divide the thermocouples onto several items by applying the parameters previously exposed to the oven load. For the treatment of more complex products, such as, for example, in the treatment of fixed tubesheet exchangers or in the case of particular materials, Trater applies double thermocouples in the most critical points, with a back-up function in the event of failure.


In Trater, temperature recording is continuous and automatic throughout the thermal cycle. It is carried out with multi-point reading recorders with a written trace or with data acquisition devices capable of recording the entire thermal cycle and reproducing it in graphic or digital printing. The data collected are used by the operator responsible for monitoring the treatment to verify that, during the cycle, no anomalies are occurring that could compromise the result of the treatment. They are finally used as final documentation of the work performed (time/temperature diagram).

For the control of particularly complex thermal cycles to be adopted on very delicate items, with a very high number of thermocouples (up to 72 recording points), our IT technicians have developed a particular software for the simultaneous management of all the readings, able to indicate in real time to the operator responsible for controlling the treatment, the progress of the thermal cycle, calculate the maximum temperature deviations to compare them with the admissible ones and calculate the average temperature distributions on parts of the item (for example in the exchangers : the average temperature of the shell, the average temperature of the tube bundle, the average temperature of each tube sheet, etc…).


Each diagram indicates the identified number of the treatment, the date of performance and the identification data of the treated items. The number and type of thermocouples used, their precision class, the time and temperature scale are also specified, as well as the signature of the Technical Manager of the treatment.


As seen, a suitable arrangement of the thermocouples on the items to be treated and a valid recording of the thermal cycle will guarantee reliable control of the treatment temperature; However, we will not be able to have reliable results if the thermometric equipment used is not able to provide a sufficient accuracy or if it is subject to vary its measurements over time. For this reason, at Trater, all thermometric equipment is calibrated before its use in the plant and periodically, in relation to the conditions of use.

Once a thermocouple has been manufactured (or purchased), it is subject, over time, to losing its accuracy due to various factors such as:

  • the alternation of thermal cycles;
  • high temperatures;
    environmental contamination;
  • mechanical stresses.

These factors, by changing the characteristics of the materials, vary the thermoelectric power and, consequently, the measurement. It is very difficult to estimate the life of a thermocouple in general, as it depends on various factors, even unpredictable ones, as in the case of mechanical stresses.
It is better, however, not to leave too long a period between one calibration and the next, so as not to incur measurement errors in a large number of treatments. In Trater we carry out a six-monthly calibration for K-type thermocouples in reusable sheaths and a quarterly calibration of the recorders.

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