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Real-time Multi-Method Corrosion Monitoring (MMCM)™

Patent Pending 1206253.5

The Problem

Internal corrosion of metallic pipelines, piping and vessels causes many hundreds of millions of pounds of damage in industry every year and hundreds of millions are also spent combating it in industries ranging from oil and gas to nuclear to water treatment. Methods used to combat internal corrosion range from building in a corrosion allowance, using corrosion resistant alloys, coating, scavenging corrosive species or by introducing corrosion inhibitor.

To ensure that the chosen corrosion mitigation technique is being successful it is useful to be able to monitor the corrosion rate in-situ; in the event, for example, that corrosion is occurring too fast, in-situ monitoring allows intervention and re-evaluation of the mitigation technique. It can also be useful to allow inhibition injection rates to be optimised, with direct impact to reduce operational costs such as chemical costs, maintenance costs, shut-down costs and replacement/repair costs as well as minimising lost production and reducing the risk of very costly leaks.

Corrosion rate monitoring is usually done by inserting probes through the wall of the pipeline, piping or vessel and measuring corrosion with one of several well established techniques such as electrical resistance or weight loss. These probes can intrude into the pipeline, piping or vessel into which it is being installed, or may be used in a “flush” system where the intention is that the probe or coupon remains flush with the wall of the pipeline, piping or vessel such that it does not affect the flow pattern ir interfere with the passage of cleaning or inspection tools

Precise flush-placement is difficult to achieve, but in order to try and accomplish this, the physical dimensions of the coupon or probe is usually limited to a few square centimetres. In addition monitoring is very location specific, ie if a flush probe is in the 6 o’clock position on a horizontal line it is not able to detect corrosion occurring at the top of the line. inserting probes into the produce stream will alter the flow characteristics and this is likely to affect the corrosion rate as determined by the probe so it is unlikely that the rate determined by the probe will represent the corrosion rate of the internal wall of the pipeline, piping or vessel accurately.

Unfortunately any form of monitoring which requires a breach in the wall of the vessel creates a potential hazard, especially if the pipeline, piping or vessel operates at pressure, in particular inserting and retrieving probes requires special precautions to prevent product leakage. In addition, in some instances access to pipeline, piping or vessel may not be possible or is difficult; eg. subsea pipelines, many buried onshore pipelines and downholes. Each monitoring technique has technical limitations so it is good practise to use several of them simultaneously, a so-called “suite” of techniques, especially in critical applications.

The Solution

Our solution is to use a multi-method corrosion monitoring device (MMCM), a full-bore, approach which circumvents many of the issues of conventional corrosion monitoring.

The device is a pressure containing spool with the same internal diameter as the pipeline, piping or vessel being monitored. Working elements of the device are insulated except for the inwards facing part of the element, the working surfaces, which contact the transported fluid. This device is installed into a section of the mother-pipe and is enclosed in a larger, pressure containing, pipe. Pressure behind the working elements, in the annulus between them and the pressure containing outer pipe, is allowed to equalise with pressure inside the pipe.

In addition to temperature and pressure sensors each spool comprises of a number of monitoring elements. Each of these elements is electrically isolated from the equipment being monitored and from each other and each has several electrical connections, which allow connection to a multiplex switching unit and from there to a monitoring and recording unit. The device requires that a small amount of power is transmitted along these lines (depending on the size of the elements and the corrosivity of the fluids).

By manufacturing the working elements from the same material as the equipment being monitored and providing the spool with the same internal diameter as the equipment being monitored the MMCM does not interfere with flow, remains flush and allows us to introduce much larger monitoring elements than traditional through-wall probes. The number, length and orientation of the individual elements is determined at the design stage and takes account of operating pressures, likely corrosion mechanisms and fluid. In addition because the corrosion measuring spool is not a pressure containing barrier the thickness of the elements may be reduced so that it equals the corrosion allowance, increasing measurement sensitivity.

The multiplex unit allows each element to be interrogated by the control unit in a number of ways to provide a suite of corrosion monitoring techniques within a single device:

  1. The resistance between any pair of individual elements can be measured. This is a useful indication of water drop out in oil lines for example and condensation forming in gas lines.
  2. The resistance from one end of an element to the other end of the same element can be measured allowing corrosion rates to be determined from changes in resistance. Temperature compensation can be achieved by measuring against the secondary elements also contained it the spool.
  3. Electrochemical measurements, such as linear polarization resistance measurements, can be made on any of the elements using any other element, or the pipe wall or an introduced cell as the reference. These electrochemical measurements allow corrosion rates to be calculated.
  4. Electrochemical noise measurements (ECN) can be made on any element using any other element or the equipment or an introduced reference. ECN measurements are useful indicators of the effectiveness of corrosion mitigation using chemicals such as oxygen scavengers or inhibitors.
  5. By allowing individual elements and individual pairs of elements to be interrogated the pipe can be monitored around 360 degrees and the orientation of corrosion can be determined; this is a useful indication of the type of corrosion occurring.

Of course not all corrosion monitoring methods are applicable to all environments but with MMCM you can tailor the device to your environment and the suite of techniques can then evolve in-situ as data is collected and as your fluid compositions changes.

We are currently seeking commercial partners.