Metal corrosion is unavoidable and has the potential to cause catastrophic assets failure, which can lead to expensive downtime, operator injuries, and cause environmental damage.
Fortunately, corrosion within a pipeline, tank or vessel is easily measured. A weighed sample, known as a coupon, with the same chemical composition as the metal to be monitored is introduced into the system and then removed after a predetermined time interval. All corrosion residues are removed and the coupon is weighed again. The weight loss is converted to a corrosion rate (CR) or metal loss (ML) rate. This process helps to identify where and why corrosion occurred, the type of corrosion, and the corrosion rate.
Coupons are a good way to estimate internal corrosion rates of pipelines, storage tanks and processing equipment. (Learn more about coupons in Corrosion Coupons: Why Relying on One Test Method Isn't Enough.) All that is required for this corrosion measurement method is a suitable type of coupon, a corrosion coupon holder, and a way to remove the corrosion residue without disrupting the underlying metal substrate.
Corrosion Monitoring Saves Time and Money
Ideally, corrosion coupon holders are easy to insert and retract under pressure so systems can be monitored under normal operating conditions. The coupon is removed without venting or draining the process intermediates, so there is no operational downtime. The data obtained from corrosion monitoring helps:
- Determine whether the equipment requires maintenance
- Prevent catastrophic failures or leaks
- Extend the equipment’s asset life
- Enhance system uptime and save money
The proper tools facilitate best practices for corrosion monitoring and ensure systems continue to operate at peak capacity. Generally, corrosion coupon holders can accommodate flat rectangular, rod, electromagnetic, disk or flush style coupons. Additionally, a sample probe, drip pot assembly or quill can be incorporated to collect samples of process intermediates at the same place where the coupon is located. (Discover more ways to test for corrosion in Corrosion Assessment: 8 Corrosion Tests.)
Historically, corrosion monitoring equipment required three people using a specialized device to install and retrieve corrosion coupons. The tool might weigh 65 kg (143 lbs.) including the service valve, and often required the use of a jib crane for safety. Retrieving this type of corrosion monitoring device from high-pressure lines is hazardous, strenuous and expensive, especially in areas with limited space, such as offshore oil rigs.
A Better Way to Handle Corrosion Coupon Holders
The best corrosion coupon holders are lightweight, yet strong and durable. They provide for safe, fast and cost-effective insertion and retraction under pressure. Preferably only one insertion tool is needed for multiple systems, and is easily operated by only one operator. These corrosion monitoring and chemical injection tools are designed for both low- and high-pressure systems up to 10,000 psi (689 bar) MAOP at 38°C (100°F). They can be inserted by hand or mechanically to meet most application needs.
Mechanically inserted corrosion coupon holders used in high-pressure systems (about 500 to 5,000 psi) require tools to insert and remove them from the system without process interruption. The best insertion tools have a side handle crank so the operator is able to work from a stable and secure position to the side of the tool. In addition, they can be operated upside-down or in any other position for hard to access locations, and are non-telescoping to minimize the space needed for operation.
Some tools are designed to remain in the pressurized system. A locking collet secures the tool in the process stream until removed by the operator. Long travel lengths (up to 25 feet) for the tool holders allow a corrosion coupon to be placed at the optimum place in the process.By having one, easily operated corrosion monitoring and chemical injection tool that can be used for multiple systems, customers can save significantly on both tools and labor without sacrificing quality, efficiency or safety.