Description
Introduction
Corrosion coupons can be used to test the corrosion rate in different industries, such as the oil and gas industry and the water industry. The EMT-RCC Retractable Corrosion Coupons come with a retrieval tool that makes it possible to take the coupon apart for pipelines under pressure. The designed pressure is below 10 MPa. During operation, the implantation depth of the corrosion coupon can be adjusted to accommodate the pipeline’s diameter and wall thickness. The standard system is available in various lengths—24, 30, 36, 42, and 48 inches (to meet customer needs)—making it suitable for pipes of different diameters. The EMT Retractable Corrosion Coupons comprise a corrosion coupon, a ball valve, and an adjustable safety clamp kit. It is recommended to use the safety closure when the pipeline pressure drops below 1500 psi and the temperature falls below 500 °F.
Understanding the Test Results: Take the Water System as An Example
The corrosion rate of a coupon is determined by the amount of metal lost over a specified period. To determine metal loss, the coupons are meticulously weighed and reported before and after. Corrosive “pitting” is also quantified by measuring the area of the pitted surface.
Location, exposure length, pH, water temperature, coupon design or placement, flow velocity, and current water treatments are all factors that influence the corrosion rate.
Following the evaluation, the technician will compute the rate in mils per year. Each metal or alloy has a different allowable corrosion rate.
Stainless Steel
| Evaporative Water Systems | Closed Water Systems | |
| Acceptable | <0.1 MPY | <0.1 MPY |
| Unacceptable | >0.1 MPY | >0.1 MPY |
Copper and Copper Alloys
| Evaporative Water Systems | Closed Water Systems | |
| Pretty Good | <0.1 MPY | ≤0.1 MPY |
| Very Good | 0.1-0.25 MPY | 0.1-0.15 MPY |
| Good | 0.25-0.35 MPY | 0.15-0.20 MPY |
| Fair | 0.35-0.5 MPY | 0.2-0.3 MPY |
| Poor | 0.5-1.0 MPY | 0.3-0.5 MPY |
| Unacceptable | >1.0 MPY | ≥0.5 MPY |
Low Carbon Steel
| Evaporative Water Systems | Closed Water Systems | |
| Pretty Good | ≤1.0 MPY | ≤0.2 MPY |
| Very Good | 1.0-3.0 MPY | 0.2-0.3 MPY |
| Good | 3.0-5.0 MPY | 0.3-0.5 MPY |
| Fair | 5.0-8.0 MPY | 0.5-0.8 MPY |
| Poor | 8.0-10.0 MPY | 0.8-1.0 MPY |
| Unacceptable | >10 MPY | ≥1.0 MPY |
Aluminum
| Evaporative Water Systems | Closed Water Systems | |
| Acceptable | <0.2 MPY | <0.2 MPY |
| Marginal | 0.2-0.25 MPY | 0.2-0.25 MPY |
| Unacceptable | >0.25 MPY | >0.25 MPY |
Components of EMT Retractable Corrosion Coupons
| Safety Clamp Assembly | This part guarantees that the system is securely attached to the pipeline. It is intended to withstand the system’s high pressure and temperature conditions. |
| Lock Nut | The lock nut is critical in locking the system and preventing it from loosening due to pipeline vibration or pressure variations. |
| Sealing Nut | The sealing nut, in conjunction with the lock nut, forms a secure and tight seal, preventing pipeline leakage. |
| Connection Pipe | This is the system piece that links the corrosion coupon to the pipeline. It is built to endure the same pressure and temperature levels as the pipeline. |
| Full Bore Ball Valve | The flow of the pipeline media is controlled by this valve. It can either fully halt or allow full flow, which is critical for system maintenance and operation. |
| Welded Base | The welded base serves as the coupon system’s foundation, providing a robust and sturdy platform for the other components. |
| Coupon Mounting Rod | This rod secures the corrosion coupon and is adjustable to fit various pipeline diameters and wall thicknesses. |
| Adjustment Nut | The adjustment nut allows the corrosion coupon to be precisely positioned within the pipeline. This is essential for acquiring precise corrosion data. |
| Upper Safety Clamp | This clamp attaches the system’s upper portion and works in tandem with the bottom safety clamp to guarantee the system is securely fastened to the pipeline. |
| Locking Nut | The locking nut adds an extra layer of protection to the system by ensuring that the coupon position modifications remain fixed throughout the operation. |
| Lower Safety Clamp | This clamp secures the lower portion of the system, collaborating with the higher safety clamp to provide a tight and secure connection to the pipeline. |
Reinstallation of EMT-RCC Retractable Corrosion Coupons
When the corrosion coupon replacement is completed or reinstalled after the inspection, proceed with the reinstallation of the coupon device. Proceed with the reinstallation of the coupon device when the corrosion coupon replacement is completed or reinstalled following the inspection work.
(1) Check to see if the adjustment rod is in position.
The distance between the two safety clamps should be measured and adjusted (L2 = 515525mm). If it does not fit this condition, its range should be adjusted. (Note: During the adjustment procedure, keep the lower safety clamp stationary and only adjust the upper safety clamp.)
(2) Replace the sealing compound.
Clear the residual sealing material from the branch pipe threads and the sealing nut, then wrap the new sealing material around the threads.
(3) Connect the coupon device.
Align the coupon device with the branch pipe threads, hand-tighten it until it doesn’t move, and then tighten the sealing nut with a wrench.
(4) Turn on the valve.
Check for leaks at the branch pipe connection and any threaded connections after opening the valve. Close the valve if there is a leak, then deal with the leaking seal (change the sealing material or replace parts, maintain, and reinstall). If there is still a leak, repeat this process until no leakage exists.
(5) Return the upper safety clamp to its original position.
Adjust the lower adjustment nut of the upper safety clamp to the lowest position as soon as it affects the upper adjustment nut’s adjustment. To the original installation record distance L, adjust the distance between the upper safety clamp and the surface of the welded base; see step 4 of the initial installation. When tightening the nuts, one person can alternately tighten the two nuts, or two persons can tighten the two nuts simultaneously, striving to keep the upper safety clamp perpendicular to the coupon support rod to avoid excessive tilt.
(6) Snap the Coupon Support Rod into place.
After adjusting the upper safety clamp, verify the direction of the coupon support rod and turn it such that the indicator surface points in the direction of the pipeline medium flow. Tighten the upper and lower adjustment nuts of the upper safety clamp, and inspect and tighten the lower safety clamp’s lock nut. The installation is finished.
The reinstallation process is now complete.
Conclusion
The EMT-RCC Retractable Corrosion Coupon provides a critical tool for assessing corrosion rates in various industries, including the oil, gas, and water sectors. The retractable design, adjustable implantation depth, and various lengths make it a versatile solution for pipes of different diameters and wall thicknesses. This system, comprising a corrosion coupon, a ball valve, and an adjustable safety clamp kit, offers a practical, safe, and efficient method for corrosion analysis under different pipeline conditions.
Understanding the test results, such as the degree of metal loss and pitting, is crucial for maintaining the integrity of these systems. Factors like location, exposure length, pH, water temperature, coupon design or placement, flow velocity, and current water treatments significantly influence the corrosion rate. With the EMT-RCC Retractable Corrosion Coupon, industries can monitor and manage corrosion effectively, ensuring the long-term operational efficiency and sustainability of their pipeline systems.
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