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Case Study

Replacing corrosion coupons with permanently installed ultrasonic sensors

Corrosion coupons have been widely used for over thirty years throughout the Oil & Gas industry as a means of calculating the rate of internal corrosion at various strategic locations on assets. They are sacrificial pieces of material, that are inserted in-line and can be used to determine the corrosivity of a system, and/or the effectiveness of corrosion mitigations, such as inhibitors. Typically, the coupons are collected after a length of time as part of a retrieval campaign, and the weight lost is measured to output a corrosion rate value.

Despite being widely used, corrosion coupons can be limited in a number of different ways:

There have been several serious incidents over the years that have occurred during the retrieval process which has led to a large proportion of asset owners to ban live line retrievals and move the operation to shut down. This now means battling for bed space with other high priority work scopes with the result of either drastically reduced retrieval campaigns or cancelled mobilisation and no data at all, and this is a problem, as asset owners are stretching out the duration of shutdowns meaning no data for an extended period.

I have spoken to OIMs in the past who never slept very well when these retrieval campaigns were ongoing due to the risks involved, risk to life, potential breaks in containment, galled plugs resulting in a permanently installed retrieval tool until the next shutdown window, heavy duty covers falling off after due to vibration, sized caps that need machined off and flanges refacing all because they have not had regular maintenance.

Then there is competency, there are a number of highly competent professional companies out there that provide these services to a very high standard, but then there are those who don’t. I have seen many pictures of retrievals online where there is an obvious lack of understanding in the retrieval process and the changes that have been made over the years to this procedure to increase the Engineers safety as well as those around them.

Adding to this, collection campaigns can be very expensive, time consuming and the resulting data of the campaign can be delayed as the report can be issued weeks after the coupons have been retrieved.

Permanently installed sensors as an alternative?

Ultrasonic thickness sensors provide an alternative, ‘in-situ’, source of internal corrosion rate data, by measuring the thickness loss of the pipe/vessel itself over a period of time. They are designed to be permanently installed on the surface of pipework/vessels and offer reproducible, accurate ultrasonic thickness measurements from the same location each time.

The cost-effective WAND sensors from Inductosense are activated wirelessly by a handheld data collector or by a remote data collector and a measurement can be acquired in a few seconds. You don’t have to be a specialist inspector to use the WAND – anyone can use it.  Thanks to the unique, embeddable design of the technology, measurements can even from underneath coatings, insulation, or hard-to-reach areas, furthermore due to the low cost of these sensors it is conceivable to install a higher number of sensor locations and increase the volume of data you have for your asset.

Internal corrosion rate data can be collected much faster, by personnel already on the asset, and without need for any downtime as the sensors are non-intrusive. Collecting data with WAND means personnel are not prone to the same safety risks associated with retrieving coupons.

Inductosense has now deployed WAND sensors as an alternative to corrosion coupons on multiple assets. The graph below shows the cost benefit of replacing 40 corrosion coupons (assuming an annual retrieval rate) with 40 WAND sensors. The operator can start to save costs from year 2 by using personnel already on the asset to collect data. In addition personnel are kept out of harms way as the data collection is non intrusive.