Thin-layer activation

Considerable corrosion monitoring is carried out utilising invasive methods, i.e. where the corrosion sensor is required to penetrate the pipe or vessel wall. Avoidance of penetration using non-invasive methods (thin layer activation, ultrasonics, radiography and magnetic fingerprinting) is receiving considerable developmental attention. 

Thin layer activation (TLA) has a long experience in monitoring or measuring wear and erosion. A small quantity of radioisotope tracer is introduced into the metal surface which can be either a coupon or component. Metal loss due to corrosion (provided the corrosion product is non-adherent) can be detected remotely with high sensitivity . 

Asher, J., Conlon, T. W., Tofield, B. C. and Wilkins, N. J. M., Thin Layer Activation-A New Plant Corrosion Monitoring Technique , Proc. Conf. On-Line Surveillance and Monitoring , entitled On-Line Monitoring of Continuous Plants, Ellis Horwood, London (1983)... 

The most important techniques are -> tracer methods (i), Mossbauer spectroscopy (ii), neutron activation (iii), thin layer activation (TLA) (iii), ultrathin layer activation (UTLA) (iii), and positron lifetime spectroscopy (iv). 

Thin layer activation - radiochemical (nuclear) methods in electrochemistry... 

An excellent way of measuring the material loss at the surface is use of thin-layer activation. A thin layer of radioactive tracer is produced on the surface by irradiation with charged particles. This technique can be applied to all types of iron, steel, nonferrous metals and alloys. It is particularly suitable for metal wear studies, because, if done carefully, the charged-particle activation little alters the mechanical properties of the surfaces of specimens. As the charged particles for irradiation, protons, deuterons, a particles, and occasionally He-particles accelerated by a cyclotron or other accelerators are used. Choosing the kind and energy of the charged particles, a radioactive layer of 10-1,000 pm thickness is produced. Typical nuclear reactions used are as follows. 

Thin layer activation coupons have been used to continuously monitor corrosion rates in continuous digesters, and to verify the effectiveness of anodic protection systems [180], The surface of a thin layer activation coupon is irradiated to a shallow depth and monitoring is performed with a Geiger counter 6x>m outside the digester wall. Subtracting for effects of half-life decay, the corrosion rate can be estimated from the decreased activity of the coupon. 

Radiochemical methods, such as tracer methods [1-3], Mossbauer spectroscopy [4], neutron activation [5], thin layer activation (TLA) [5], ultrathin layer activation (UTLA) [5], and positron lifetime spectroscopy [6], are applied for the study of a wide range of electrochemical surface processes. The most important areas are as follows adsorption and electrosorption occurring on the surface of electrodes the role of electrosorption in electrocatalysis deposition and dissolution of metals corrosion processes the formation of surface layers, films on electrodes (e.g., polymer films), and investigation of migration processes... 

Disposal is not normally a heavy expense for hydraulic systems and monitoring devices. There are some instruments that are radioactive, with thin layer activation, but not a serious level. 

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