Testing and certifying marine device mooring fixtures

Mooring fixtures secure marine energy converter (MEC) devices to the seabed. There are many types of MECs, for example floating wave or tidal devices.

Mooring system prepared for installation offshore (Photo: Dublin Offshore)

MECs are often located in demanding environments. Several aspects must be considered when choosing the right mooring, such as water depth, type of seabed (sand, clay, rocky or hard), water current and wind conditions. The mooring must provide the required compliance or stretch of the line as it moves under the water, as well as reliability.

Moorings are an important part of the overall MEC system. Failure to adequately secure a device, could result in costly repairs or even put a device out of service.

IECRE, the  IEC System for Certification to Standards Relating to Equipment for Use in Renewable Energy Applications, offers testing and certification for the marine, solar photovoltaic and wind energy sectors, to IEC International Standards.

e-tech spoke with Andrew Hunt, Technical Associate who carries out mooring inspections at the European Marine Energy Centre (EMEC), to find out more about the process. EMEC was designated as the first IECRE renewable energy testing laboratory (RETL) for the marine sector in 2020.

What does a typical mooring scheme look like?

A typical mooring scheme will be attached to a buoy, tidal energy converter (TEC) or wave energy converter (WEC). There will be some sort of anchor at one end of the mooring lines or chains, which attaches to the MEC at the other. There may also be an export cable transmitting power and communications from the device to the shore; alternatively there may be wireless communications mounted on the buoy connected to a test mooring system to transmit critical mooring load data as well as metocean and position information back to shore.

How do you carry out the mooring inspection?

We use IEC Technical Specification (TS) 62600 - Part 10, Assessment of mooring system for marine energy converters (MECs), developed by IEC Technical Committee (TC) 114 for marine energy - wave, tidal and other water current converters. The TS provides uniform methodologies for the design and assessment of mooring systems for floating MECs and can be applied at different stages, also for installation and maintenance of floating MEC plants. It can be used for mooring systems of floating MECs of any size or type in any open water conditions.

We also use ISO/IEC 17020, Conformity assessment — Requirements for the operation of various types of bodies performing inspection. This standard covers aspects such as: impartiality and independence, requirements for personnel, facilities and equipment, inspection methods and procedures, including the handling of items and samples, as well as inspection records and certificates and document management.

Having both standards is helpful, because IEC TS 62600 - Part 10 is still developing, and will need further feedback from industry and stakeholders, which takes time.

While some aspects of inspection are not mentioned directly in the current TS Part 10, ISO/IEC 17020 includes a provision for us to accommodate client needs, as well as deliver the contents of Part 10.

What does the mooring inspection cover?

There are typically three phases to the mooring inspection:

Phase 1: Scoping

We establish the work scope with the client (TEC or MEC device developer), create the data acquisition (DAQ) log and Master Document List (MDL) and carry out an initial compliance assessment with IEC TS 62600 - Part 10. The latter may well shape the overall work package for the client.

Phase 2: Planning

This phase covers various aspects of data collection. We then produce an interim report bringing together the outputs of the work so far and have further meetings with the client to ensure we have thoroughly prepared the inspection plan in line with our internal procedures and documentation.

Phase 3: Inspection

Finally, we conduct the inspection and update and maintain the DAQ log and MDL. We use this information to produce the final report required for the issuance of the inspection certificate, which is the last step of the process.

How important is the data gathering process?

The inspection process builds confidence in the data gathered and so we take the data gathering process very seriously. It is imperative to verify the integrity of information. For example, if we have an item of data that says something weighs 10 tons, we must be sure that this data is accurate and that an error has not occurred somewhere in the process.

Calculations, data checks and time of recordings are therefore vital. When we reach the phase of an assessment where we have been given the data, we must do an audit to ensure we are seeing true data and that we have done a robust job.

Data for our inspection purposes comes in a variety of formats and is not limited to what most people would think of as data in the form of raw and processed output from sensors. It could include formal project documentation (technical design reports, calibration certificates, GA drawings etc) and photographic and video of actual eyes on inspections (now due to the COVID-19 situation being carried out remotely where practicable using a video link).

What is particularly useful about the 62600-10 standard?

The TS Part 10 is designed for MECs; it is all encompassing geared mainly towards design of mooring systems.

However, for clarity it provides a good overview and description of different mooring options while offering guidance to other standards that provide more detailed requirements.

Both these aspects make it particularly useful guide for device developers, who are generally more focused on the device itself rather than all the other requirements to keep it safely secured to the seabed.

How does EMEC use IEC standards?

EMEC uses IEC standards as a basis for many inspections and develops internal governing documents and a standard operating procedure document to ensure inspections are carried out in a consistence manner from project to project.

We must carry out this internal work for delivery of the inspection service and to comply with ISO/IEC 17020. We are audited against our governing documents by the UK accreditation service (UKAS). There is a full audit every three years and smaller ones annually. UKAS looks at our processes and procedures and makes sure we follow ISO/IEC 17020.

We must show documentation or evidence that we are following the standard and how we apply it. The data and the accuracy of these internal documents are very important.

How do you contribute towards the development of the standards you use?

Lessons are learned with different clients. For example, a client may be more interested in the data from the device tests rather than the design. Our current challenge is that the Part 10 standard is more focused on the design than the data. We have managed this issue so far by being clear about our role in the work scope phase. Then we fall back on the ISO/IEC 17020 for the parts not covered directly in Part 10. Our experience allows us to give constructive feedback to IEC TC 114 once we conclude our projects and offer some clear, robust suggestions for the standard.

Another point we have noted is that IEC TC 114 seems to be looking at long-term moorings, but many projects are for short-term deployments. This raises questions such as would a short-term deployment need to consider mooring corrosion? In other words, if the project is for a few months, do we need a detailed corrosion study or could a bigger, stronger chain be used for the shorter period? There needs to be a trigger in the standard for such situations, which is currently missing.

What challenges have you faced during COVID-19?

Ever changing and increasingly stringent measures to control the virus presented significant challenges to conduct face to face inspections.  For example, projects have a number of weeks allotted for the inspection. However, the time required for inspectors to quarantine before being allowed to travel to the site was the same as this inspection time. The inspectors then had to self-isolate upon their return.

Fortunately, technology came to the rescue, and we were able to carry out inspections using a video call, often over a mobile phone.  It is not as quick as a face-to-face inspection, but it worked.  We could still ask the client to show us specific things, such as for example serial numbers of equipment.

A couple of times we encountered unreliable internet connections during inspections.

Remote inspections are certainly here to stay in the short term.  As they can provide a cost effective and lower carbon footprint method of inspection, they are certainly an option going forward.

Find out more about IECREIEC TC 114 and EMEC.