Corrosion mounting procedures

One procedure is to use test specimens in the form of discs which can be rotated at the desired speed while either wholly or partly immersed in the testing solution, and Freeman and Tracy described a device of this sort in a contribution to the ASTM Symposium on Corrosion Testing Procedures. With their apparatus the specimen discs were mounted on horizontal shafts and were partially immersed in the testing solution. 

Recommended methods for assessing the corrosivity of waters, including flowing potable waters, are described in ASTM 02688 1983. Three procedures are described in which test specimens in the form of wires, sheets or tubes are placed in pipes, tanks or other equipment. The test assembly for the first of these consists of three helical wire coils mounted in series on, and electrically insulated from, a supporting frame. The assembly must be installed so that flow is not disturbed and turbulence and high velocities, e.g. of more than 1 -53 ms , are avoided. A minimum test period of 30 days is recommended. Procedures for the other specimen forms are given in the standard. 

Other workers have published improved procedures for inspecting both reinforced concrete and prestressed concrete structures with regard to determination of the embedded steel components [110]. A prototype ultrasonic procedure was developed to determine the condition of prestressed and pretensioned tendons in concrete. The application of electrochemical surface-mounted systems for estimating the rate of corrosion of reinforcing steel and other embedded steel components in large concrete structures was described using this technique. 

The use of corrosion coupons is included in the test procedure as a means for monitoring corrosive activity within a given chamber. A minimum of six corrosion coupons, made of 25.4 X 50.8 mm AISI 1006-1010 steel, are used. The coupons are cleaned and weighed in accordance with the procedure described in J2334 and mounted in a nonmetallic rack. One coupon from each end of the rack is removed, cleaned, and reweighed every 20 cycles. At the present writing, no target mass loss numbers for each cycle or end-of-test mass loss have been published. 

Coupon tests are by far the most commonly used test method. The usual method is to mount coupons in the middle of a stream, frequently in a serpentine bypass loop as shown in Fig. 3. Detailed procedures for coupon tests are described in ASTM D 2688, Test Method for Corrosivity of Water in the Absence of Heat Transfer (Weight Loss Methods) (Method A). Tests with very low water flow (suspended coupons in the cooling tower basin, for example) are not recommended unless the objective is to measure corrosion under near stagnant conditions. 

Laboratory exposure tests are usually conducted in chambers similar to that described in ASTM B 117, Test Method of Salt Spray (Fog) Testing. Because the environment is more corrosive than the salt fog described in ASTM B 117, the variations described in ASTM G 85, Practice for Modified Salt Spray (Fog) Testing, are often used. Some investigators have used a modified procedure in which the test coupons are mounted over holes on the outside wall of the exposure chamber so that they can be subjected to a thermal gradient [35]. Outside mounting of the coupons also affords the opportunity to conduct in situ electrochemical impedance measurements. 

As described in detail in the RILEM 124 SRC recommendation (RILEM, 1994), the basic repair methods for carbonation induced corrosion consist in repassivation of the steel by a mortar layer or by local repair. The procedure for patch repair is described in the published guidelines (e.g. Bentur et al., 1997). Limitation of the concrete moisture content is another repair principle, its aim is dry out the concrete, e.g. when additional facade elements are mounted to reduce energy consumption. When carbonated concrete is not completely removed in the vicinity of the reinforcement, corrosion occurs after repair when sufficient moisture is present (Schiessl and Breit, 1996). 

The combination of macroscopic wear tests, corrosion tests, and study of the microscopic changes induced by ion implantation suggests a possible quality control procedure based on measurement of the implantation profiles and on corrosion tests. Both can be performed quickly using small test samples mounted alongside the knee joints in the implantation chamber. 

---