Corrosion coupons, probes, holders are corrosion-sensing devices that can detect the rate of corrosion in any process environment.
Corrosion coupons are probably the oldest and simple and very effective method for corrosion and erosion studies that take place in a specific operating system and alert facility operations and/or service companies if action is needed before too much damage takes place to the system. Corrosion coupons are also known as corrosion monitoring coupons. Corrosion monitoring coupons provide precise corrosion rate monitoring in any process environment and they are beneficial in terms of:
- Maintenance and Repair costs
- Measurement of material failure
- Inexpensive means of in-operations monitoring
- Equipment’s remain life can be accurately predicted
Corrosion detection technique can also be applied to prevent scales in pipelines, wells, and injection manifolds, etc.
Corrosion coupons can be done by observing the mils-per-year (MPY) corrosion rate exposed in the operating system, valuable data can be extracted regarding the life expectancy of materials.
Coupons are pieces of metal that are available in any sizes, shapes, and materials. Coupons should be composed of the same chemical composition to the pipeline or vessel or the equipment that is being monitored. Coupons are exposed to corrosive solution similar to that in process facilities on a regular basis can give information of the corrosion rate and type.
Corrosion coupons are typically stenciled with alloy and sequence numbers for proper identification, and usually include mill test reports identifying element compositions of materials used.
The typical types of corrosion coupons are:
- Strip Coupons - with two mounting holes, can be utilized for varied studies; this is the most widely used coupon for all corrosion monitoring.
- Strip Coupons - this is widely used in sets at intervals in the line, and with narrow ports or low-pressure equipment.
- Disc Coupons – normally used in applications where the coupon cannot extend into the pipe to interfere with the flow, and typically applied in multiple or stacked monitoring applications. A disc coupon has one mounting hole that is countersunk, and uses a flathead screw, insulating washer and insulating disc for mounting.
Corrosion coupons are typically designed and came with:
- ASME B31.3
- NACE MR0175 / ISO 15156
- Coupon Holder
- Suitable for use with Hydraulic Retrieval Tool
An equivalent uniform corrosion rate can be calculated from the sample weight loss, using a simple ASTM formula:
V = −[K*ΔM/(ρ*S*t)]
V is corrosion rate (μm/year)
∆M is sample weight variation (mg)
ρ is alloy density (g/cm3)
S is area of the sample exposed to the medium (cm2)
t is exposure duration (h)
K is a non-dimensional coefficient (= 8.76*106, with the units used for the other terms).
Corrosion Probes are electrical resistance corrosion monitoring devices used in many industries to monitor real-time corrosion rate without removing corrosion probe.
Corrosion Coupon Holders are used to suspend corrosion coupons in the area to be monitored. The coupon holders work with a variety of corrosion coupons, including rod (cylinder), flat (strip) single hole, flat (strip) dual hole, and disk, to measure the rate of corrosion within pressurized processes such as pressure vessel, pipeline, oil wells. They can be mounted in any orientations to meet project requirement.