A general technique of deciding corrosion rates is by utilizing corrosion coupons, which are even in size, pre-measured segments of metal. Corrosion coupons, illustrative of system metals, are embedded into a coupon rack established on the system to be monitored. Typically, system water is permitted to flow over the corrosion coupons for about 30 – 90 days. The coupons are then evacuated and given back to a lab where they are sanitised and re-weighed. From this weight reduction and the measurements of the coupon, a corrosion rate in mils/year (mpy) is ascertained. 1.0 mil/year converts into 1/1,000th of an inch of metal wastage every year.

The following describes various types of attack that can be seen on coupons:

• Generalized Attack – Even corrosion on whole surface of the coupon. Not typically a worry unless the mpy is increased.
• Corrosive Attack – A normal term given to any incision on the metal surface brought about by corrosion. Pits can differ significantly in size, depth and thickness. Under 10 pits for each side is sometimes named isolated corrosion.

Precise observation of corrosion rates in any kind of surrounding is essential when perceived in terms of upkeep and repair costs connected with corrosion and material lapse. Test coupons give a reasonable method for on-line checking that will permit you to adequately quantify the corrosivity in your framework. By examining the mils-per-year corrosion rate of an uncovered coupon, valuable data can be given with respect to the material’s survival expectancy.

Crystal Industrial from India can design coupons in any size, form, or material you require. Corrosion Coupons can be designed with metal combination and series of numbers for appropriate identification. Process test reports, distinguishing element mixtures of materials utilized, are given on all requests.

While requesting for test coupons, please be ready to furnish the businessperson with data in regards to the kind of material you are examining, the style and size of the coupons you need, surface finish required, and if appropriate, mounting opening size and area.

Corrosion rates can differ amongst welded and non-welded metals, hence it is advised to observe the behaviour of both situations. Studies include inspection of the parent material, the heat-influenced zone, the weld metal, and the surfaces between all metals included. The surface impacts generated by welding, formation of heat-tint or oxidation, fluxing activity of slag, and the deliquescence of slag can be significant parameters in the corrosion response of metals.

Ideally, the corrosion coupon utilized must be a similar thickness and welded with an indistinguishable welding process from the material utilized in the manufacturing instrument. Generally this is not reasonable so a representative sample should be examined.

Typical welding systems utilized are Shielded Metal Arc (SMAW), Gas Tungsten Arc (GTAW), and GAS Metal Arc (GMAW). Samples are ground smooth followed by welding, unless generally indicated, to give an even surface for microscopical examination.

Finishes

Crystal Industrial’s Corrosion Coupons can be provided with a range of finishes according to your specific application. Few of the common finishes accessible are characterized beneath:

Mill – finish as manufactured from mill.
120 Grit – fine finish utilizing a 120 grit belt and usually utilized in corrosion examinations, for example, pitting surveys, where even surface finish is required. Finishes up to 600 grit(exceedingly fine) can be given by utilizing belt sanders.

Twofold Disk Ground – super fine finish utilizing an unsmooth disc that leaves negligible residue. Very good for examinations where surface finish is crucial.