Effective dose in the manufacturing process of rutile covered welding electrodes

Abstract

Shielded metal arc welding using covered electrodes is the most common welding process. Sometimes the covering contains naturally occurring radioactive materials (NORMs). In Spain the most used electrodes are those covered with rutile mixed with other materials. Rutile contains some detectable natural radionuclides, so it can be considered a NORM. This paper mainly focuses on the use of MCNP (Monte Carlo N-Particle Transport Code) as a predictive tool to obtain doses in a factory which produces this type of electrode and assess the radiological impact in a specific facility after estimating the internal dose.To do this, in the facility, areas of highest radiation and positions of workers were identified, radioactive content of rutile and rutile covered electrodes was measured, and, considering a worst possible scenario, external dose at working points has been calculated using MCNP. This procedure has been validated comparing the results obtained with those from a pressurised ionisation chamber and TLD dosimeters. The internal dose has been calculated using DCAL (dose and risk calculation). The doses range between 8.8 and 394 μSv yr(-1), always lower than the effective dose limit for the public, 1 mSv yr(-1). The highest dose corresponds to the mixing area.

Effective dose in SMAW and FCAW welding processes using rutile consumables

“…The covered electrodes chosen for this work were rutile type, as it is the most commonly used type and the one which has the highest radioactivity content [9]. Among the different existing brands of this electrode, the one most commonly used in Spain was chosen.…”

“…It must be taken into account that the rutile used to produce these consumables is not always the same; there are different types based on the mineral type and its origin. However, in the composition of the rutile mineral there are always traces of radioactive substances, mainly 238 U and 232 Th natural radioactive series [9], and as a result industries that use this material are or may be classified as NORM industries.…”

“…The first results of our previous study [9] revealed that workers exposed to rutile throughout the manufacturing process of rutile-covered electrodes do not receive a dose exceeding the established limit for members of the public, 1 mSv yr −1 , this dose being essentially external. However, during welding processes the expected worker's dose is mainly internal, and it is this dose which is assessed in this paper.…”

“…Although the radionuclides found in the covering of rutile type electrodes and in flux cored wire are in equilibrium [9], they are not emitted in the same way into the air during welding. Depending on their chemical properties, some go mainly to the slag, like Ra, and others to the air, like Po.…”

“…Rutile (mainly titanium dioxide, TiO 2 ) contains a variable amount of natural radionuclides, and this amount is the largest among all the materials used to produce non-thoriated electrodes. The radioactivity of this material depends mainly on its origin [9] and ranges between 0.1-1.0 and 0.07-0.45 Bq g −1 for the U and Th radioactive series, respectively [10]. Depending on the producer, rutile is used at a variable rate; for instance, in the production of this specific type of arc welding consumable rutile constitutes 50% of the covering.…”