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DNV-OSS-312 Certification of Tidal and Wave Energy Converters [Table of Contents] Sec.2: Principles and Process

DNV-OSS-312 Certification of Tidal and Wave Energy Converters

[-] Sec.1: Introduction

SECTION 1
Introduction

Sec.1
A. Introduction

Sec.1
A 100   General

Sec.1 A
101   This Offshore Service Specification presents the principles and procedures for DNV services with respect to Certification of tidal and wave energy converters.

Sec.1 A
102   The wave and tidal energy converters being installed offshore as well as inshore will be faced with many of the same environmental challenges as oil and gas installations being installed offshore. To mitigate the risks related to the lack of operational experience in the offshore renewable industry, DNV will use its experience from the oil and gas industry duly adapted to the relevant safety levels necessary for renewable energy installations. Reference is therefore extensively given to our offshore standards and recommended practices as well as international standards.

Sec.1 A
103   Due to the specific needs and characteristics of this industry, the certification concept is extended such that it can be defined as a robust process to provide, through independent verification, evidence to stakeholders (financiers, partners, utility companies, insurers and the public) that the marine energy converter will perform adequately within acceptable levels of safety, availability, reliability, asset integrity and environmental impact, within limits specified in the certification basis and complying, where applicable, to relevant standards.

Sec.1
A 200   Organisation of this Offshore Service Specification

Sec.1 A
201   This document is divided into the main sections:
—Section 1 provides a general introduction to the DNV document hierarchy
—Sections 2 and 3 describe the principles and procedures for the certification services.

Sec.1
A 300   Objects covered

Sec.1 A
301   All different concepts of tidal and wave energy converters are covered. This document refers primarily to offshore and near shore concepts for tidal and wave energy converters, but it may also be used for shoreline devices.

Sec.1 A
302   The converters may be of fixed or floating type. They may be constructed in steel, concrete or composite.

Sec.1 A
303   This Offshore Service Specification (OSS) is general and flexible in order to match the large differences in technology and concepts being developed in the renewable energy industry. The OSS gives a framework for how the certification is applied to the marine renewable industry.

Sec.1
A 400   DNV Document hierarchy

Sec.1 A
401   DNV Offshore Publications which provide information at various levels of detail for offshore installations are organized into a three level document hierarchy, illustrated in Figure 1:
—Offshore Service Specifications (OSS series) providing principles and procedures of certification, classification, verification and consultancy services
—Offshore Standards (OS series) specifying technical requirements and acceptance criteria for general use by the offshore industry as well as providing the technical basis for classification. (For wave energy converters DNV refers to "Guidelines on design and operation of wave energy converters" a document commissioned by Carbon Trust and carried out by DNV, May 2005. The Carbon Trust is an independent company funded by the UK Government. Its role is to help the UK move to a low carbon economy by helping business and the public sector to reduce carbon emissions now and capture the commercial opportunities of low carbon technologies.)
—Recommended Practices (RP series) providing sound engineering practice as well as guidance related to the Offshore Standards.

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Fig. 1   DNV Offshore Publications Hierarchy

Sec.1
B. Definitions

Sec.1
B 100   Verbal forms

Sec.1 B
101   The terms will, can and may are used when describing DNV's actions or activities, and the terms shall, should and may are used when referring to other parties than DNV.

Sec.1 B
102   "Shall": Indicates requirements strictly to be followed in order to conform to this OSS and from which no deviation is permitted.

Sec.1 B
103   "Should": Indicates that among several possibilities, one is recommended as particularly suitable, without mentioning or excluding others, or that a certain course of action is preferred but not necessarily required. Other possibilities may be applied subject to agreement.

Sec.1 B
104   "Will": Indicates a mandatory action or activity to be undertaken by DNV. (Ref. "shall" for other parties).

Sec.1 B
105   "Can": Indicates an action or activity that DNV will not necessarily do unless specifically requested by the client (Ref. "should" for other parties).

Sec.1 B
106   "May": Verbal form used to indicate a course of action permissible within the limits of the OSS.

Sec.1
B 200   Definitions

Sec.1 B
201   Client: DNV's contractual partner. It may be the purchaser, the owner or the contractor.

Sec.1 B
202   Certification: Action by a certification body, providing written assurance that adequate confidence is provided that a duly identified product is demonstrably in conformity with a specific standard or other normative document.

Sec.1 B
203   Certification Basis: Requirements for the system's specifications, operating conditions, performance targets and reliability targets. The basis to which the system will be assessed during certification.

Sec.1 B
204   Conceptually feasible: A technology at an early stage of development is considered conceptually feasible if the main challenges have been identified and judged to be resolvable by use of sound engineering practice.

Sec.1 B
205   Failure: Termination of the ability of an item to perform the required (specified) function.

Sec.1 B
206   Fit for service: A technology is considered fit for service when the failure modes that have been identified through the systematic process outlined in this OSS have been properly addressed, and the supporting evidence substantiates that the technology fulfils all stated functional requirements and meets the stated reliability target.

Sec.1 B
207   New technology: Technology that is not proven. This implies that the application of proven technology in a new environment or an unproven technology in a known environment, are both new technology. The degree of new technology will be classified in categories to be used as input to risk assessment.

Sec.1 B
208   Prototype: An original type that serves as a model for later models, and allows for testing and improvement of the design.

Sec.1 B
209   Proven technology: In the field, proven technology has a documented track record for a defined environment. Such documentation shall provide confidence in the technology from practical operations, with respect to the ability of the technology to meet the specified requirements.

Sec.1 B
210   Risk: The qualitative or quantitative likelihood of an accident or unplanned event occurring, considered in conjunction with the potential consequences of such a failure. In quantitative terms, risk is the quantified probability of a defined failure mode times its quantified consequences.

Sec.1 B
211   Risk reduction measures: Those measures taken to reduce the risks to the operation of the technology and to the health and safety of personnel associated with it or in its vicinity by:
—reduction in the probability of failure
—mitigation of the consequences of failure.


Sec.1 B
212   Surveillance: The process of inspecting tests, calibrations or other activities to assure that the necessary quality is maintained. Once the device is in operation, reviews carried out to assure that operation is within safety limits, and is maintained within limiting conditions.

Sec.1 B
213   Technology qualification: A confirmation by examination and provision of evidence that the new technology meets the specified requirements for the intended use. Hence, qualification is a documented set of activities to prove that the technology is fit for service.

Sec.1 B
214   Verification: An examination to confirm that an activity, a product or a service is in accordance with specified requirements.

Sec.1
C. References

Sec.1
C 100   DNV documents

Sec.1 C
101   This document will make reference to relevant documents in the DNV document hierarchy and where appropriate to internationally accepted publications, codes and standards.

Sec.1 C
102   The Offshore Standards listed in Table 1 shall be used for documentation of tidal and wave energy devices. The Recommended Practices and Class Notes listed in Table 2 shall be used. Only those DNV standards and recommended practices that are assumed to be relevant for energy converters are listed in Table 1 and Table 2. Reference is also made to the Guidelines on Design and Operation of Wave Energy Converters (Commissioned by Carbon Trust, and carried out by DNV May 2005).

Sec.1 C
Table 1 DNV Documents relevant for Tidal and Wave Energy Converters 
Reference Title 
DNV-OSS-121 Classification based on performance criteria determined from risk assessment methodology 
DNV-OSS-300 Risk-based verification 
DNV-OSS-401 Technology qualification management  
DNV-OS-A101  Safety principles and arrangement  
DNV-OS-B101  Metallic materials  
DNV-OS-C101  Design of offshore steel structures, general (LRFD method)  
DNV-OS-C102  Structural design of offshore ships  
DNV-OS-C103 Structural design of column-stabilised units (LRFD method) 
DNV-OS-C104 Structural design of self-elevating units (LRFD method) 
DNV-OS-C105 Structural design of TLPs (LRFD-method) 
DNV-OS-C106 Structural design of deep draught floating units (LRFD method) 
DNV-OS-C301  Stability and watertight integrity  
DNV-OS-C401  Fabrication and testing of offshore structures  
DNV-OS-C501 Composite components 
DNV-OS-C502 Offshore concrete structures 
DNV-OS-D101 Marine and machinery systems and equipment 
DNV-OS-D201 Electrical installations 
DNV-OS-D202 Instrumentation and telecommunication systems 
DNV-OS-D301 Fire protection 
DNV-OS-E301  Position mooring  
DNV-OS-F201  Dynamic risers  
DNV-OS-J101 Design of offshore wind turbine structures 
DNV-OS-J102 Design and fabrication of wind turbine blades  
DNV Rules Rules for planning and execution of marine operations 

Sec.1 C
Table 2 DNV Recommended Practices, Classification Notes and Standards for Certification 
Reference Title 
DNV-RP-A203 Qualification procedure for new technology 
DNV-RP-B401 Cathodic protection design 
DNV-RP-C102 Structural Design of Offshore Ships 
DNV-RP-C103 Column Stabilised Units 
DNV-RP-C201 Buckling strength of plated structures 
DNV-RP-C202 Buckling strength of shells 
DNV-RP-C203 Fatigue analysis strength of offshore steel structures 
DNV-RP-C204  Design against accidental loads  
DNV-RP-C205 Environmental conditions and environmental loads 
DNV-RP-C206 Fatigue methodology of offshore ships 
DNV-RP-C207 Statistical representation of soil data 
DNV-RP-E301 Design and installation of fluke anchors in clay 
DNV-RP-E302 Design and installation of plate anchors in clay 
DNV-RP-E303 Geotechnical design and installation of suction anchors in clay 
DNV-RP-F205 Global performance analysis of deepwater floating structures 
DNV-RP-H101 Risk management in marine and subsea operations 
Standards for certification 
No. 2.4 Environmental test specification for instrumentation and automation equipment  
No. 2.5 Certification of offshore mooring steel wire ropes 
No. 2.6 Certification of offshore mooring chains 
No. 2.9 Approval Programmes - related to components (incl. e.g. hydraulic cylinders), manufacturers, service suppliers.
(Freely downloaded from our website: exchange.dnv.com) 
No. 2.13 Standard for certification of offshore mooring fibre rope 
Classification Notes 
CN 30.4 Foundations 
CN 30.6 Structural reliability of marine structures 
CN 30.7 Fatigue assessment of ship structures 
CN 33.1 Corrosion prevention of tanks and holds 
CN 41.2 Calculations of gear rating for marine transmissions  
CN 41.4 Calculations of shafts in marine applications for marine transmissions  
CN 45.1 Electromagnetic compatibility  
Guidelines and recommended practices 
No. 20 Corrosion protection of ships  

The majority of the above documents in the DNV hierarchy may be accessed via DNV's website: http://webshop.dnv.com/global/

Sec.1
C 200   International standards

Sec.1 C
201   Internationally recognised standards may also be used in design and construction of tidal and wave energy converters.

Sec.1
D. Safety Philosophy

Sec.1
D 100   General Considerations

Sec.1 D
101   Targets for the certification process and the certification basis, should be based on an overall safety philosophy covering all phases from conceptual studies up to and including decommissioning.

Sec.1 D
102   A safety philosophy should be derived considering the following aspects and stakeholders:
—risk to life (during installation and removal, access to device during in-service life, risk to navigation and others during in-service life)
—environmental impact due to any fluid releases, anti-fouling coatings, bilge water, and location of site relative to sensitive environments (protected species or sensitive sites and visual impacts)
—loss of power generation
—inspection and maintenance cost, risks during removal of equipment for inspection and maintenance
—reputation of developer, industry, concept (survivability of the device in extreme conditions is very important in terms of reputation)
—underwriter perception of risks and definition of premium value (during installation and removal, and in-service life)
—financial or venture capital communities' perception of risk to the return on investment
—safety level expected by Authorities. This may include Authority requirements in other countries which are potential marketing targets for the devices.


Sec.1 D
103   In general, when selecting safety level, safety classes can be defined as:

Safety Level Low - where failure implies low risk of human injury and minor environmental and economic consequences.

Safety Level Normal - for temporary conditions where failure implies risk of human injury, significant environmental pollution or high economic, asset damage or political consequences. This level normally aims for a risk of less than 10-4 per year of a major single accident, which corresponds to a major incident happening on average less than once every 10 000 installation years. This level equates to the experience level from major representative industries and activities.

Safety Level High - for operating conditions where failure implies high risk of human injury, significant environmental pollution or very high economic or political consequences.

Sec.1
D 200   Structures

Sec.1 D
201   The requirements for wave energy devices can be covered in large parts by codes for offshore steel structures as in DNV-OS-C101 (DNV-OS-C501 for composite components and DNV-OS-C502 for concrete structures). These provide internationally acceptable levels of safety by defining minimum requirements for structures and structural components.

Sec.1 D
202   DNV-OS-C501 is a comprehensive and generic design and fabrication code for structures and components using composite materials (laminate or sandwich).

Sec.1 D
203   DNV-OS-C502 is particularly adequate to wave energy conversion (WEC) devices that consider the use of concrete as the ratio between wave responses and dead load response will generally be high. In this load situation, most other standards are not applicable. For offshore concrete structures this especially applies to fatigue calculations. DNV-OS-C502 is in fact very similar to NS3473 (which would be equally applicable to WEC devices) except for some areas. The most important difference is fatigue Wøhler curves for reinforcement.

Sec.1 D
204   In DNV-OS-C502 the results of a British research project "Concrete in the Ocean" are implemented and these Wøhler curves are stricter than the Wøhler curves in NS3473 and in the Eurocode. NS3473 and Eurocode base their fatigue curves on reinforcements not exposed to a marine environment, i.e. no corrosion fatigue.

Sec.1 D
205   The load response part of DNV-OS-C502 is very similar to the draft ISO code (ISO/DIS 19903) for offshore concrete structures. This code may also be an alternative once it is finally agreed.

Sec.1 D
206   For temporary phases (e.g. installation or removal), requirements are given in the DNV Rules for Planning and Execution of Marine Operations. This uses a somewhat higher probability of failure when compared to requirements for in-place survival condition, as these marine operations can be characterised by single event operation with implementation of special procedures and better control of environmental limits, etc. DNV-RP-H101 provides guidance and recommendations on how to reach an acceptable and controlled exposure to risk during marine operations for personnel, environment, assets and reputation.

Sec.1 D
207   The consideration of selected safety class can be taken into account for some aspects of the structural design such as: the definition of Design Fatigue Factor, derivation of characteristic loads, definition of load factors to be applied (see DNV-OS-C101 Sec.2 D404), definition of accidental loading (see DNV-OS-A101 Sec.2 D103) and selection or structural category (DNV-OS-C101 Sec.4 C200 - taking into account the significance of components in terms of consequence of failure).

Sec.1
D 300   Equipment and Systems

Sec.1 D
301   Safety classes shall be considered while defining redundancy or safety features for the equipment and systems. Reliability is also an important aspect to be taken into account.

Sec.1 D
302   Because wave and tidal energy devices are usually unmanned, the overall risk level to personnel will be low. However, because of the difficulty in access for maintenance and the potential penalty of downtime in terms of providing energy to the grid, a higher level of reliability may be required than would otherwise be the case.

Sec.1 D
303   To obtain such a level of reliability, with limited or non-existent reliability data for marine renewable conditions and through the use of standard off-the-shelf equipment, where it is possible, requires early consideration of strategies leading to reliability/availability required and maximum level possible of maintenance and repair. Some examples of such strategies are given below:
—a low utilisation of mechanical strength, or a higher reserve, sometimes referred to as the safety factor is employed
—redundancy of equipment - this is usually applicable to electronic and moving parts
—rigorous testing of moving parts subject to cyclic loads
—rigorous testing of components subject to various environmental loads
—use of well-proven components
—a thorough FMEA study.

Sec.1
E. Certification Deliverables

Sec.1
E 100   Deliverables

Sec.1 E
101   The final conclusion from the certification will be documented by a specific agreed deliverable. The deliverables indicate the incremental nature of the certification process with each stage contributing to the next step. The deliverables provide for the gradual increase in detail and scope from the concept stage through to certification of a fully developed product. Typically these deliverables will be termed as follows:

Sec.1 E
102   Reports:
—Statement of Feasibility
—Design Assessment
—Product Certificates for Components and Assemblies
—Survey Reports
—Certificates:
In order to account for the different stages in the development of the device DNV may issue the following certificates:
—DNV Prototype Certificate
—DNV Conditioned Type Certificate
—DNV Type Certificate
—DNV Project Certificate.

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Fig. 2   DNV Certification Process


Sec.1 E
103   Statement of Feasibility - A document issued by DNV affirming that, at the time of assessment, the new technology is considered conceptually feasible and suited for further development and qualification according to the principles outlined in DNV-RP-A203.

Sec.1 E
104   Design Assessment - During the design assessment stage, intermediary deliverables such as letters with comments and reports should be issued indicating progress and identifying gaps in the information provided by the Applicant. The conclusion of the design assessment process should be documented by a Statement of Design Assessment.

Sec.1 E
105   Product Certificates for Components and Assemblies - Certificates issued by DNV regarding different components including design appraisal, manufacturing surveillance and factory acceptance testing.

Sec.1 E
106   Survey Reports - Reports issued by DNV surveyor addressing the issues related to surveillance activity that may cover different stages such as manufacturing, testing, commissioning and installation.

Sec.1 E
107   Prototype Certificate

Certificate issued to enable testing of prototypes and is based on design evaluation. This certificate implies that all the certification steps up to the issue of this certificate were successfully carried out (statement of feasibility, design assessment, fitness for purpose and manufacturing surveillance) for the specified location/conditions. The location of the device is stated on the certificate and the period of validity is limited up to 3 years. The issue of the Prototype Certificate is based on successful evaluation by DNV of:
—prototype design, including installation procedures
—prototype fabrication surveillance
—installation surveillance
—final acceptance/commissioning inspection
—periodic inspection.

During the prototype design evaluation, matters with no safety implication within the period of validity can be considered at a higher level with the use of simplified methods (sufficient to demonstrate that the risk of significant damage to structure and equipment is minimised), pending operational data from the prototype and any resulting design changes. Those issues will be assessed based on existing knowledge and with uncertainties to be clarified, under controlled circumstances, during the prototype test stage. Items including safety concept, support structure and mooring system shall be analysed in detail.

Sec.1 E
108   Conditioned Type Certificate

The Conditioned Type Certificate is issued to allow for 0-series production as well as to allow for outstanding matters with no safety implication. The Conditioned Type Certificate is based on full certification scope with the exception that outstanding matters are allowed. The outstanding matters are however limited to:
—matters with no safety implication within the period of validity (maximum 1 year)
—matters related to the finalization of manuals and quality control procedures
—matters related to the finalisation of inspections regarding the implementation of the design-related requirements in production and installation.

Provisions can be made for upgrade of Conditioned Type Certificate to Type Certificate for a particular device, subject to conditions agreed between the Applicant and DNV.

Sec.1 E
109   Type Certificate

The Type Certificate is issued for production model with no outstanding issues (validity of 5 years subject to annual endorsement).

Sec.1 E
110   Project Certificate

Within the Project Certification scope it will be assessed whether the metocean conditions, other environmental and electrical network conditions, and soil properties at the site conform with those defined in the design documentation for the energy converter. Any additional site specific designs and/or design changes related to the energy converter are considered within the Project Certification. These in general include foundations, support structure and moorings. The Project Certificate includes the design, manufacturing, installation and commissioning of the wave/tidal farm including cable laying and additional structures required for the transport and connection of the farm to the grid or the consumer.

Sec.1 E
111   These documents/certificates will make reference to the standards, regulations and other specifications which have formed the basis of the certification, and will be backed up by a traceable record documenting the information considered and the considerations made in arriving at the final status of the verification work.

Sec.1 E
112   Qualification and testing of new technology will be documented separately. See also Sec.2 B600.

DNV-OSS-312 Certification of Tidal and Wave Energy Converters [Table of Contents] Sec.2: Principles and Process