DNV CLASSIFICATION OF MOBILE OFFSHORE UNITS
By Svein Flogeland
Global Service Responsible Offshore Classification
1. Introduction
乖的英文From time to time, DNV is asked by urs and potential urs of our classification rvices
'What is covered by class', 'What is covered on behalf of authorities' etc.
This memo is written in respon to general inquiries of this nature and may be ud for information and as basis for more in-depth discussions. The memo mainly contains excerpts from DNV rules and survey check lists to illustrate actual coverage for various types of Mobile Offshore Installations.
It is worth noting that the actual coverage by class will vary between classification societies. This memo address matters and issues covered by DNV, with no attempt of comparing our scope to that of other societies.
The distribution of this document is open and unrestricted.
2. General
Classification is a comprehensive verification rvice providing assurance that a t of requirements laid down in rules established by the classification society are met during design and construction, and maintained during operation of a ship or an offshore unit. The rules are aimed at ensuring safety against hazards to the unit, personnel, and against hazards to the environment. The rules are developed by the classification company also referring to internationally accepted technical standards.
Classification has gained world-wide recognition as reprenting an adequate level of safety and quality, by way of applying experience and peak technical competence in developing rules and performing approval and surveys.
Classification implies an activity, in which a ship or an offshore unit is surveyed during construction on the basis of design approval, tested before being taken into rvice, and surveyed regularly during its whole operational life. The aim is to verify that the required safety standard is built in, obrved and maintained.
Having assigned class, DNV will issue a classification certificate and enter the main particulars and d
etails of class in the classification register. With reference to what is stated above, any certificate issued by a classification society is related to a t of rules which will vary from society to society, and also as a function of time since the rules are updated and revid on a continuous basis. It is therefore of utmost importance to be aware of the technical references for a certificate in order to understand what the certificate actually covers. For DNV clasd units, the technical references are indirectly given through a t of class notations in the certificate, as well as the initial year of classification. Technical requirements stated in the rules valid at that time will follow the unit later, meaning for instance that a classification certificate for a rig from 1992 may have different requirements associated with it than a corresponding certificate for a rig from 1982, although the class notations may be the same. A summary of currently available class notations is given in Pt. 4 below.
3. Assignment of class
Having assigned a specific class implies that DNV:
•has been satisfied that the object meets the Rule requirements for the particular class •will, through a system of surveys, verify that the requirements stipulated for retention of class are complied with.
圣帕特里克节
When assigning class to an offshore unit where the Administration of a flag state undertakes approval and surveys of systems/equipment covered by the Rules, DNV may accept their decision on the items as basis for assigning class.
For units permanently placed on location and intended for production and storage of hydrocarbons, DNV may also accept decisions by the authority with jurisdiction over the waters in which the unit is to operate (shelf state) as basis for assigning class.
4. Class notations
Clasd units will be given a class designation consisting of:
•construction symbol (mandatory)
•main character of class (mandatory)
•basic design notation (mandatory)
•rvice notation (mandatory)
•system and special facility notations (voluntary)
•special feature notations (voluntary).
construction symbol will be given to units built under the supervision of DNV,
The
whereas the symbol will be given to units built under the supervision of a recognid
•
classification society and later assigned class with DNV.
Main character of class is reprented by the notations 1A1 or OI.
The notation 1A1 will be given to mobile offshore units with hull, marine machinery and equipment found to be in compliance with the basic (common) requirements of the applicable DNV offshore standards referred to in the rules.
The notation OI will be given to non-lfpropelled floating offshore installations intended for long ter
m rvice at one offshore location with main structure, utility and safety systems found to be in compliance with the basic (common) requirements of the applicable DNV offshore standards referred to in the rules.
The basic design notation indicates the type of structure. The notations currently in u are as follows:
Basic design
notation
Description
Ship-shaped
番茄面
Unit Monohull ship and barge type units having displacement hulls with or without propulsion machinery.
Column-stabilid
年终奖怎么扣税Unit Unit dependant on the buoyancy of widely spaced columns for floatation and stability for all modes of operation
Self-elevating
Unit Unit with hull of sufficient buoyancy for safe transport which is raid above a surface on legs supported by the a bed during operation.
Deep-draught
Unit Floating structure having a relatively deep draught to obtain high heave natural period avoiding resonance respons. A DDF can have single or multi- vertical columns, with or without moonpools
Tension-leg
Unit A buoyant installation connected to a fixed foundation by pre-tensioned tendons
Units constructed according to DNV Offshore Classification Rules, arranged for a particular rvice and found to be in accordance with the relevant requirements for such rvice, will be given a corresponding rvice notation.
The rvice notations currently in u are defined below:
Service notation Description
Drilling Unit with drilling as a main function
sum函数Well Intervention Unit with well intervention as a main
function
Accommodation Units primarily ud for accommodation
purpos
Crane Units primarily ud for heavy-lift
purpos
Offshore Support Units intended for offshore support
functions (fitted with only parts of
equipment necessary to perform main
functions)
Oil Production Unit or installation with production of
hydrocarbons as a main function
Oil Storage Unit or installation with storage of
hydrocarbons as a main function
Units having special facilities, systems or equipment found to satisfy specified class requirements will be given a corresponding system or special facility class notation. Such notations may typically be DRILL, CRANE, POSMOOR, DYNPOS etc., which means that DNV has performed initial approval, fabrication survey, testing and in-rvice survey of subject systems/equipment in accordance with the technical standards referred in the Rules covering the class notations.
5. Coverage of class
The extent of a DNV survey will vary depending on whether it is a fabrication or in-rvice survey. For the latter, the extent will also vary through a class period, which normally contains one Renewal Survey, one Intermediate survey and three annual surveys in the 5-year period for which a DNV class certificate is valid. The exact coverage and extent is given in the DNV rules which should be carefully read to comprehend the exact scope for any survey. Main class covers the following main areas:
耳聋耳鸣咋治•Structural strength and redundancy
•Materials and welding
•Corrosion protection
•Stability
•Watertight and weathertight integrity
•Power generation百日攻坚行动
•Propulsion (as applicable)
•Temporary and emergency mooring
•Fire detection and extinction
•Structural fire protection
•Hazardous areas and ventilation
•Electrical systems and equipment
•Automation and instrumentation
•Emergency shut down systems
•Fuel oil systems
•Ballast systems
•Drainage and bilge pumping
•Sounding systems
•Leak detection (as applicable)
•Equipment for towing (as applicable)
•Jacking system (as applicable)
Detailed survey check lists adequately reflecting the rule requirements are available for all class notations, and may be submitted to owner for information upon request.
6. Statutory surveys
DNV is delegated authority by a number of Flag Authorities, meaning that we will carry out surveys on their behalf. Some Flag Administrations have developed own rules which then form the formal reference for such surveys, whereas the majority refers to the IMO MODU CODE as applicable standard for mobile drilling units.
The MODU CODE address 3 main aspects; the construction, the safety equipment and the radio system The construction part is fully covered by DNV's main class, the radio system requires parate surveys by specialists, and the safety equipment is subject to a dedicated survey addressing the following main topics:
•Protection of crew
•Stability documentation
•Mooring equipment
•Mooring system supply boat to rig
•Navigation
•Collision prevention
•Navigation communication
•Fire and explosion prevention
兰花画法•Fire resistance
•Fire detection and alarm
•Gas detection and alarm
•Fire fighting
•Means of escape
•Emergency power generation and distribution
•Emergency operations
•Evacuation and life-saving
•Shut down and safety systems
•Storing of explosives
•Operations and training manuals
•Helicopter deck
•Helicopter refuelling
•Helicopter deck fire fighting arrangement
•Dynamic positioning system documentation
