Corrosion Coupon Access Fitting

Corrosion Coupon Access Fitting is a standard metal coupon hung in the test vessel or on the heat exchanger or test pipe for corrosion measurement. It can monitor or evaluate the corrosion of cooling water system. So if you need anything, you can click here to contact our professionals.

Purpose of Corrosion Coupon Access Fitting:

Generally, the metal test pieces after pretreatment and weighing are placed in the test system for a period of time (such as 30 ~ 90 days). Then we take it out, observe the corrosion, clean and weigh it. Determine the weight loss degree of metal corrosion (in mils / year or mm / year, 1mpy=0.0254mm/a), corrosion type and pitting depth, etc. In addition to the influence of corrosive medium, the data of metal coupons are also related to the surface treatment of coupon, placement position, exposure time, and sample metallurgy method.

The standard corrosion test pieces for water treatment are the Corrosion coupon, cooling water treatment standard corrosion coupon, corrosion coupon, etc. The materials are an A3 carbon steel test piece, 20# carbon steel test piece, stainless steel test piece, brass test piece, red copper test piece, aluminum test piece, cast iron test piece, etc.

Storage and Use of Corrosion Coupon Access Fitting

1. Scrub the standard corrosion test piece with degreasing in distilled water, and then rinse it with distilled water for 15 seconds.
2. Scrub the standard corrosion test piece twice with absorbent cotton in chemically pure absolute ethanol (50ml/ 10 pieces);
3. The user places the standard corrosion test piece on the dry filter paper and blows it dry with cold air;
4. The standard corrosion test piece is wrapped with filter paper, placed in a dryer, and weighed for use after 24 hours;
5. The originally packaged test pieces shall be placed in a place free of corrosive gas and stored against moisture;
6. The unsealed but unused standard corrosion test pieces are still placed in the antitrust paper and placed in the dryer.

New hanging piece treatment

1. Immerse the new coupon in absolute ethanol and scrub it twice with absorbent cotton;
2. Then move it into clean absolute ethanol and soak it for a moment;
3. Put it on the clean filter paper and dry it with cold air;
4. Wrap it with filter paper, put it in a dryer, and weigh it for use after 24 hours (the weighing accuracy is 0.1g).

Treatment method of post-hanging piece

1. Take out the used hanging piece carefully, observe and record the surface condition before processing;
2. If the corrosion deposition is not obvious, we can wipe it with a drawing eraser. Make it show the true color of the metal. Then immerse it in absolute ethanol and scrub it twice with absorbent cotton. Then immerse it in clean absolute ethanol for a moment, take it out, and put it on a clean filter paper. Dry it with cold air and wrap it with filter paper. Put it in a dryer and weigh it after 24 hours (weighing accuracy to 0.1g). Calculate the corrosion rate after weight loss;
3. For the coupon with more corrosive deposits, the corrosion products shall be removed by the chemical cleaning method first.

Corrosion rate calculation formula

Corrosion rate =87.6 △ w/ (s) ρ ts mm/a
△ W – a weight loss of test piece, Mg;
S – the total surface area of the test piece, cm2;
ρ— Density of metal, g/cm3 (carbon steel 7.85, brass 8.50);
T – experimental time, h;
A (DM2): area of the coupon
Type I ——0.28 DM2 =28cm2
Type II ——0.20 dm2=20 cm2

Principle of coupon corrosion test method

1.Test purpose

• Master the principle of the gravimetric method;
• Master the method of determining the corrosion rate of hanging pieces by the gravimetric method.

2.Test principle

a. Gravimetric method

Due to corrosion, the weight of the material will change systematically. This is the theoretical basis for determining the corrosion resistance of materials by the gravimetric method. In recent years, many new Corrosion Coupon Access Fitting research methods developed a lot. However, the gravimetric method is still the most basic method for quantitative evaluation of corrosion and has been widely used. The gravimetric method is simple and intuitive, which is suitable for laboratory and field tests. It is divided into the weight gain method and the weight loss method.

(1) Weight gain method

When corrosion products are firmly attached to the sample, they are almost insoluble in solution. It is not defiled by external substances. At this time, the degree of corrosion damage can be measured by the weight gain method. The weight gain method is applicable to the evaluation of overall corrosion and intergranular corrosion, but not applicable to other types of local corrosion. The test process of the weight increase method is to measure and weigh the pre-prepared sample and place it in the corrosive medium. After the test (together with the fallen corrosion products), take it out, dry it, and then weigh it. All the weight gain indicates the corrosion degree of the material.

In the gravimetric method, a sample usually provides only one data point on the corrosion time curve. When the corrosion products are firmly attached to the surface of the sample and have constant components, the weight gain can be measured continuously or periodically on the same sample. Therefore, this method is suitable for studying the law of corrosion rate changing with time.

A serious disadvantage of the weight gain method is the indirectness of the data. That is, the obtained data includes the weight of corrosion products. Exactly how much material is corroded needs to be converted by analyzing the chemical composition of corrosion products? Sometimes the phase composition of corrosion products is quite complex, and accurate analysis is often difficult. At the same time, multiagent metals (such as iron, copper, etc.) may produce several corrosion products with different chemical compositions, which are difficult to convert. These all limit the application scope of the weight gain method.

(2) Weightlessness method

Weightlessness is a simple and direct method. It does not require corrosion products to be firmly attached to the material surface, nor does it consider the solubility of corrosion products. Because all corrosion products must be removed from the sample after the test. The weight-loss method directly represents the weight of materials lost due to corrosion, without the chemical composition analysis and conversion of corrosion products.

The test process of the weight loss method is to measure and weigh the pre-prepared sample and put it in the corrosive medium. After the test, take it out, clean, dry, and weigh it after removing all corrosion products. The weight loss of the sample directly characterizes the corrosion degree of the material. Whether by weight gain method or weight-loss method, before and after the test, during the test, and before and after the removal of corrosion products, it is necessary to carefully observe and record various changes on the material surface and in the medium.

b. Evaluation of gravimetric determination results

The gravimetric method measures the corrosion rate according to the weight change of the sample before and after corrosion. In order to make the data of different tests and different samples compare with each other. We must use the weight change per unit area in unit time as the unit, that is, the average corrosion rate.

The corrosion rate of metal is not constant in the corrosion process. In other words, the instantaneous corrosion rate may change. The gravimetric method only calculates the average corrosion rate. Therefore, it is not suitable for measuring the instantaneous corrosion rate. In addition, the corrosion rate determined by the gravimetric method is usually only applicable to the type of uniform corrosion. Due to the different densities of various metal materials, even if it is uniform corrosion, this unit of corrosion rate cannot represent the loss depth of corrosion. Therefore, the average corrosion rate can be converted into the average erosion depth per unit time.

c. Methods of removing corrosion products

Generally, there are three methods:

Mechanical method, chemical method, an electrolytic method.

• Mechanical method. Generally, first, rinse with tap water and scrub with a rubber or bristle brush. Or scrape with a wooden scraper or a plastic scraper. This method can remove most of the loose corrosion products. However, it is necessary to completely remove corrosion products to accurately test or inspect local corrosion conditions. Further chemical or electrochemical methods are necessary.
• Chemical method. Select the appropriate chemical solution and operating conditions, and remove the corrosion products on the surface of the sample by dissolution. In order to protect the metal matrix, retarding agents are often added to the solution of chemical removal. These methods are quite simple. However, it may damage the substrate during use, resulting in test error. For this reason, clean the same size blank sample of the same material without corrosion under the same conditions while cleaning. Seek its weightlessness. Then subtract the times from the weight loss of the actual sample to obtain a more realistic weight loss of the sample.
• Electrochemical method. Select the appropriate anode and electrolyte, take the sample as the cathode, and apply direct current to the electrolysis method. During electrolysis, the cathode produces hydrogen, which makes the corrosion products peel off under the mechanical action of hydrogen bubbles. Mechanical methods can wash away residual loose substances. This method is effective and the weight loss of the blank sample is small.