The below mentioned information describes various types of attacks that can be seen on coupons.
Generalized Attack
Even corrosion over whole surface of the coupon. Not generally a worry unless the mpy is high.
Pitting Attack
A general term given to any crevice on the metal surface due to corrosion. Pits can differ substantially in size, depth and also thickness. Under 10 pits for each side is sometimes named isolated pitting. Copper plating, low inhibitor levels, under-deposit attack or high chlorides can all lead to pitting.
Localized Areas of Attack
Usually the consequence of under-deposit corrosion. May show the requirement for better deposit control and additionally low stream rates through the coupon rack. If the crevice indicates concentric rings with the most intense ingress in the focal point, it might be because of corrosive microbes attack, for example, can be caused by microbiologically induced corrosion (MIC).
Copper Plating
It is an outcome of the accumulation of dissolvable copper on mild steel or other non-copper amalgams. Copper plating can lead to extreme galvanic corrosion and metal failure because of pitting attack.
Edge Attack
Since the edges of coupons are extremely stressed while manufacture, they have a tendency to be preferential areas for corrosion. Edge attack does not usually show a major issue unless extreme.
Attack Under the Coupon Holder
If metal failure is restricted to the region under the coupon holder, this may simply symbolize the impact of the coupon holder to quicken under-deposit or crevice attack and not indicate the attributes of the recycling water. Despite the fact that these impacts can’t be disposed off from corrosion rate computation, they must be considered when interpreting the outcomes. Protecting the coupon holder and screws are affixed firmly limits these impacts.
Establishment Notes
1. Crystal Industrial’s corrosion coupons from India are sanitized and precisely weighed before delivery. They must not be handled any more than required when established. Keep away from oil, fingerprints, or grease contact. Utilize a paper napkin or identical covering while handling of the coupon before establishment. The coupon must be joined to the Teflon®* pole with a nylon screw and nut. Metallic screws and nuts will maximize the possibility of galvanic or contact corrosion at the safe end of the coupon.
2. Make sure the numbered corrosion coupons are recorded as per the system and position for appropriate correlativity. The dates of establishment and withdrawal from the system are crucial.
3. The stream must be adapted so that there is no unstability or air mixture. To prevent disintegration of copper, a stream rate of three to five feet for every second is required. A stream meter or some other sort of stream control gadget is suggested. Remember that high stream rates can add to disintegration while low stream rates (under two feet per second) can quicken corrosion and natural fouling.
4. Trials are usually 90 days. Crystal Industrial’s Corrosion Coupons from India can be examined at 30 days interims for reference and indications of destructive conditions. In monitoring the coupons, don’t tamper with the surface by scratching or removing material.
5. Commonly Crystal Industrial’s coupons from India demonstrate some fast corrosion signs at first, typically as corrosion items on the surface, especially at areas where numbered stamps are created, edges of coupons, and around the locks. The quick corrosion decreases with time. This is more common with steel than copper. Unless corrosion is critical, there must be no reason for fear.