Corrosion racks

Table 7.33 Corrosion rack tests of nickel- versus iron-base alloys used in waste incineration...

FIG. 25-4 Corrosion racks used to expose corrosion samples in operating production equipment (a) inside pipes (b) inside process vessels (c) to be bolted onto baffles and brackets with process vessels. 

Are corrosion coupons installed, using a corrosion rack Is it correctly installed Is there some form of real-time computer software in operation ... 

Fig. 10.2 Various monitoring devices (1 to r) corrosion/fouling/ biofouling mesh coupons, LPRM monitor, corrosion rack, deposit monitor, membrane filter on poured plate, and dip-slide... 

Portable deposit/corrosion monitors are typically housed in an enclosure of perhaps 30 in. H x 20 in. W x 15 in. D. Components include inlet flow controller, strainer, adjustable electric heater, (outer) see-through glass housing, (inner) heated specimen tube or block, hot/cold temperature readout, corrosion rack, plus thermal overload, low-flow cut-off, and other safety devices. The specimen tubes or blocks are available in different metals (as are the corrosion coupons) and can usually be replaced in a matter of minutes. Unlike test heat exchangers, the cooling water in this type of monitor flows on the shell side of the specimen tube. 

The deposition of crystalline scales, air-borne contaminants, biofilms, etc. tends to be higher on previously fouled or corroded surfaces than on clean surfaces. Also, deposition and fouling affect both the rates and mechanisms of corrosion on a clean metal surface. It can therefore be useful to obtain subjective information on deposition and fouling tendencies in a cooling system, provided that the methods are simple and produce results quickly. The use of blank coupons inserted in a bypass corrosion rack can often provide this support information. 

The initial corrosion racks provided by the IAEA were immersed in late 1996 in water storage pools with a wide range of water chemistry and environmental conditions, and were monitored for corrosion over a period of time. The results of these early observations were reported after 18 months at the second research co-ordination meeting (RCM) of the CRP, held in Sao Paulo, Brazil. Pitting and crevice corrosion were the primary corrosion mechanisms observed. Corrosion by deposition of iron and other cathodic particles on the... 

Additional corrosion racks were provided to the CRP participants in March 1998 at the second RCM. Most of these racks had been immersed in the individual basins by mid-1998. The surveillance racks were monitored visually for corrosion, and when corrosion was detected, the coupons were removed from the water and analysed. As found in earlier testing, water quality proved to be the key to good performance. Crevice corrosion was seen between most of the crevice couples as expected, because the pH was lower by 0.5-1.0 unit in the crevice. In poorer quality water, further corrosion was observed, espedally between bimetallic crevice coupons, to the extent that coupons had to be forced apart. The results of the individual participating laboratories were presented at the third and final RCM, held in Bangkok, Thailand, in October 2000. 

Monitoring corrosion racks at research reactor storage basins... 

After the first RCM, the participants formulated individual test plans specific to their spent fuel storage basins. A general test protocol for conducting the programme was provided by the IAEA. This protocol included instructions for preassembly, assembly and immersion of the corrosion racks in the storage basin, exposure intervals, and removal and examination. 

The individual participants were asked to prepare the corrosion racks and to begin the exposure as soon as possible. Most of the racks were assembled and immersed in fuel storage pools well before the end of 1996. Because of the limited number of racks available, participants were asked to make periodic visual examinations of the coupons to determine whether active corrosion was obvious. If corrosion was visible, the racks were to be removed from the water and the coupons photographed. The racks were then returned to the basin for additional exposure. Water chemistry measurements were made on a periodic basis and monthly visual inspections were performed by most of the participants. 

Definitions The corrosion rack is the assembled set of coupons, spacers, central support tube and hanger. A basin, pool or pond is the contained volume of water used for storage of spent fuel. In some cases the pool also contains the reactor core. 

This report describes all of the work undertaken as part of the CRP and includes a review of the state of the art understanding of corrosion of research reactor aluminium alloy cladding materials a description of the standard corrosion racks, experimental protocols, test procedures and water quality monitoring the specific contributions by each of nine participating laboratories a compilation of all experimental results obtained and the supervisory group s analysis and discussion of the results, along with conclusions and recommendations. 

An excellent example of field testing in conjunction with laboratory testing to solve a heat exchemger corrosion problem in an industrial chlorinated solvent incinerator is described in Ref 49. A corrosion rack containing three... 

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