Ongoing

COMOSEA | Data-driven corrosion monitoring for offshore wind farms

Financed by

Realistic, data-driven COrrosion MOnitoring and Management at SEA applied to offshore wind foundations

Corrosion of offshore steel structures affects their cost and lifecycle. There is currently no accurate, let alone affordable way to check for corrosion in this submerged environment. An accurate estimation of the amount of material that is expected to be lost through corrosion, is helpful in two ways: allow for smaller corrosion allowances or longer lifetimes.

COMOSEA is a research project that aims to develop a realistic approach for fleet-wide monitoring of corrosion using SCADA data from the ICCP (Impressed Current Cathodic Protection) system.

Context

For any offshore steel structure, corrosion is a major problem that causes a lot of uncertainty. It is now generally accepted that corrosion has a big financial impact through the need for extra material, corrosion protection measures and inspection costs.

The National Association of Corrosion Engineers (NACE) impact study [1] states that 3.8% of the global GDP (Gross Domestic Product) is lost every year to corrosion prevention and repair. In the maritime sector, this can even amount to 19.9% of the turn-around [2,3]. On top of that, there's a lot of uncertainty around how much corrosion to expect, where it might occur, and whether prevention measures are actually working. Underwater inspection is often difficult or even impossible, and the results are often doubtful.

Projects like MAXWind and Sirris' involvement in SOCORRO have shown that there is a need for a more realistic method of corrosion monitoring and data-driven corrosion management for large fleets of offshore, unmanned, steel structures. More long-term data from multiple sources will help to understand the phenomena and their importance.

Objective and results

What asset owners are looking for is improved lifetime models and a better estimation of end-of-life (extension or earlier decommissioning). Damage due to corrosion must be fed into these models through two channels:

a correct estimation of 'general' corrosion to know the remaining corrosion allowance (in quantitative terms);
pit sizes and shapes.

COMOSEA will concentrate on channel 1, which is currently the only method used, and uses the loss in wall thickness (corrosion allowance) to update S/N curves for fatigue-life calculations. There is still a lot of room for improvement in terms of accuracy: the real corrosion rate is today only roughly estimated, often based on theoretical information, with a large safety margin. More accurate calculations will either allow smaller corrosion allowances (so there is less use of steel and lower cost) or longer lifetimes.

COMOSEA is working on a way to monitor corrosion fleet-wide, using SCADA data from the ICCP (Impressed Current Cathodic Protection) system. This data is already collected on all foundations, which is great news for the cost/benefit ratio of corrosion monitoring.

Channel (2), using pit sizes and shapes, requires a fundamental understanding of the localised corrosion of carbon steel in a maritime environment, which is still being investigated at a low TRL level, and not yet applied in industry.

The main project outcome will be a detailed description of a measurement set-up and model to obtain a more precise estimation of remaining corrosion allowance. This will serve as an input for fleet-wide lifetime assessment and will be included in a guideline for people who own and run assets. The guideline will explain:

how cathodic protection data can be used to monitor corrosion processes across all assets,
what impact monopile design can have on corrosion,
and how to use water quality probes, coupons and corrosion probe measurements.

It will also clarify how these three aspects lead to better lifetime models.

Approach

The project approach can be summarised as follows:

The objective is to develop a method for Corrosion Monitoring and Management based on an ICCP fleet leader concept by:
Determining periods of under-protection (in which corrosion can take place) from the time of inactivity of the ICCP system.
Identifying foundations with 'abnormalities' in terms of corrosion processes taking place, from variations in ICCP current consumption which cannot be linked to changes in known parameters

A controlled ICCP experiment will be set up at the Harbour of Ostend to provide the data and insights needed to develop this model. The goal is to:

learn how protection potential declines during a period of inactivity and what the impact of environmental parameters is on ICCP current consumption.
Perform the experiment with both small and large coupons. If feasible, a test with a sample buried in the mud zone should also be conducted.
Run the experiment for a period of at least 1.5 years.

In addition, a real, long-term corrosion and ICCP data set, obtained from multiple offshore wind monopile foundations, will be built and analysed. This will allow to:

investigate dissolved oxygen (DO) inversion and correlation with pH (still to be published results from SOCORRO and MAXWind projects), the impact of monopile design, and link this to the observed corrosion rates and ICCP results.

Target group

Parties being faced with corrosion in a maritime setting and/or confined space.
Offshore wind operators employing cathodic protection.
Other sectors employing cathodic protection.

Funding

Type of project: ETF
Project nr HBC.2024.0692

Sources

[1] National Association of Corrosion Engineers (NACE). (2016). Economic Impact. Geraadpleegd op 1 juni 2023, van http://impact.nace.org/economic-impact.aspx.
[2] Koch, G. H., Brongers, M. P., Thompson, N. G., Virmani, Y. P., & Payer, J. H. (2005). Cost of corrosion in the United States. In Handbook of environmental degradation of materials (pp. 3-24). William Andrew Publishing.
[3 ]Kroon, D. H., Bowman, E., & Jacobson, G. Journal: American Water Works Association (2019)