Description
Test Coupons Experiment
Principle
The most intuitive way to judge the corrosiveness of a certain environment to a particular material is to measure the changes generated after exposing the specimen for a certain period of time, which is the basis of the coupon test and is one of the oldest forms of corrosion monitoring. It can adapt to the capacity of personnel and equipment, and can meet various needs. Comprehensive systems can be developed to evaluate the stability of general materials against total corrosion, pitting, stress corrosion cracking, hydrogen embrittlement, etc., in chemical plants or refineries. These tests are usually long-term and are very specific in terms of sample location, where the corrosion rate is the aggregate value of the total exposure time. In a given container, the medium can generally exist in three states, namely liquid, gas and liquid-gas. Therefore, in each phase, a different rate of corrosion will occur. In addition, local variations due to scour, local low speed, and temperature differences can further affect readings. Therefore, it is not enough to install a test hanger in the center of the pipe, and the resulting data may be three times higher than the corrosion of the pipe wall. Designers can specially create sample holders to expose many plates simultaneously. Unless studying bimetallic effects, you usually insulate the samples from each other and from the fixed support.Test coupons
Test coupons measure sample mass loss in corrosion tests. To increase accuracy, it is necessary to maximize the surface area to mass ratio. Test coupons can be made from disks, rods, plates, or any suitable profile. However, edges should be machined and polished to eliminate the residual stresses caused by shearing operations that can lead to preferential corrosion. It is best to avoid using rods, as localized grain boundary corrosion often alters the corrosion pattern. Appropriate heat treatment of test coupons can simulate any metallurgical condition, allowing for the collection of a wide range of data. Stressed samples can also undergo test coupon trials. The coupon method can also simulate crevice conditions or other specific scenarios.Before installing test coupons, you must remove all traces of grease, oxides, or other contaminants to improve reproducibility. You should finish the surface to approximate that of the proposed pressure vessel shell or stressed component material, typically polishing with #120 metallurgical sandpaper or lightly sandblasting, although a pickled surface might be more representative. Identifying samples is crucial; you should place markings where the sample’s holder or plastic insulation protects them. Exposed markings may disappear after corrosion, and embossed numbers on the exposed surface may activate the material. Finally, wear gloves after degreasing the samples if you handle them before installation.
Corrosion Evaluation
After exposure tests, carefully inspect the test coupons and fully document the state of corrosion products before cleaning and weighing. All accumulated corrosion products and dirt must be thoroughly removed using mechanical methods such as scrubbing or scraping; alternatively, sandblasting; or by chemical means, such as washing in a solvent or cleaning in a corrosion-inhibiting acid or alkali. At this stage, the possibility of introducing some errors arises due to the loss of uncorroded metal or incomplete removal of corrosion products. When the test duration is short, this additional increase in weight can represent a significant percentage of the total weight loss, potentially enlarging the measurement error.EMT Test Coupons Selection Model
| Model | |
| EMT-CIPA | Access Fitting Body of Corrosion Coupon |
| | | | | | |
| – The material of Access Fitting Body |
| 0 | CS |
| 1 | 316SS |
| 2 | 316LSS |
| 3 | DUPLEX SS |
| The Type of Access Fitting Body |
| B | 2″Welded（suffix “pressure rating” can be added to B） |
| F | 2″ANSI Flange（suffix “pressure rating & sealing type” can be added to F） |
| -Tee Size- pressure rating & sealing type if the flanged end |
| 0 | No Tee |
| 1 | 1/4″NPT(F)Tee |
| 2 | 1/2″NPT(F)Tee |
| 3 | 3/4″NPT(F)Tee |
| 4 | 1″NPT(F)Tee |
| 5 | Hole for 1/4″SWN Flange |
| 6 | Hole for 1/2″SWN Flange |
| 7 | Hole for 3/4″SWN Flange |
| 8 | Hole for 1″SWN Flange |
| -Protective Cover Type/ Material |
| 0 | No Protective Cover | Material |
| 1 | Without hole | CS or 0 |
| 2 | With hole | SS or 1 |
| 3 | Bleed Valve | DSS or 3 |
| 4 | Bleed Valve, & Pressure Gauge | |
| For Example, EMT-CIPA-0F600#RF-2-1/CS shows 2″ANSI 600#RF Flange Access Fitting Body in CS, 1/2″NPT(F)Tee, Protective Cover in CS without hole |
| 0F600#RF: 0F_ Access Fitting Body is Flanged in CS, 600#RF _Size is 2″ANSI 600#RF, |
| 2:Tee size is 1/2NPT(F) |
| 1: Protective cover type is without a hole |
| /CS: Protective cove material in CS |
Coupon Types
| Name | Strip Coupon | Multihole Strip Coupon | Disc Coupon |
| | | |
| Applications | Commonly used for most evaluations. | Use with low-pressure access equipment or through narrow ports that a standard 3/4 inch wide coupon cannot pass. | These circular coupons work in multiple disc monitoring applications. |
| Size | 3”*3/4”*1/16”
(76.2mm*19.0mm*3.2mm) | 3”*1/2”*1/16”
(76.2mm*12.7mm*3.2)
With mounting holes | Φ1.25”(31.8mm)Thickness 1/16”(3.2mm) |
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