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DNV-OS-C105 Structural Design of TLPS (LRFD method)
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Sec.1
A. General
Sec.1
A 100 Introduction
Sec.1 A
101 This standard provides requirements and guidance to the structural
design of TLPs. The requirements and guidance documented in this
standard are generally applicable to all configurations of tension
leg platforms.
Sec.1 A
102 This standard is based on the load and resistance factor design
method (LRFD). LRFD is defined in DNV-OS-C101.
Sec.1 A
103 A TLP can alternatively be designed according to working stress
design principles, which is defined in DNV-OS-C201.
Sec.1 A
104 A TLP can also alternatively be designed to API RP 2T as it
has been accepted that it meets the safety levels required by this
Standard.
Sec.1 A
105 A Tension Leg Platform (TLP) is
defined as a buoyant unit connected to a fixed foundation (or piles)
by pre-tensioned tendons. The tendons are normally parallel, near
vertical elements, acting in tension, which usually restrain the
motions of the TLP in heave, roll and pitch. The platform is usually
compliant in surge, sway and yaw. Figure 1 shows an example of a
tension leg platform.
Fig. 1 Example of a tension leg platform
Sec.1 A
106 The standard has been written for general world-wide application.
Governmental regulations may include requirements in excess of the
provisions of this standard depending on size, type, location and
intended service of the offshore unit/installation.
Sec.1
A 200 Objectives
Sec.1 A
201 The objectives of the standard are to:| — | provide an internationally acceptable
standard of safety by defining minimum requirements for structural design
of TLPs |
| — | serve as a contractual reference document for suppliers
and purchasers |
| — | serve as guidance for designers, suppliers, purchasers
and regulators |
| — | specify procedures and requirements for TLP units subject
to DNV verification classification and certification services. |
Sec.1
A 300 Scope and application
Sec.1 A
301 A TLP is usually applied for drilling, production and export
of hydrocarbons. Storage may also be a TLP function.
Sec.1 A
302 A TLP may be designed to function in different modes, typically
operation and survival. Also horizontal movement (e.g. by use of
catenary or taut mooring) of TLP above wells may be relevant. Limiting
design criteria when going from one mode of operation to another
shall be established.
Sec.1 A
303 The TLP unit should also be designed for transit relocation,
if relevant.
Sec.1 A
304 For novel designs, or unproved applications of designs where
limited, or no direct experience exists, relevant analyses and model
testing shall be performed which clearly demonstrate that an acceptable
level of safety can be obtained, i.e. safety level is not inferior
to that obtained when applying this standard to traditional designs.
Sec.1 A
305 Requirements concerning riser systems are given in DNV-OS-F201.
Sec.1 A
306 In case of application of a catenary or taut mooring system
in combination with tendons, reference is made to DNV-OS-E301.
Sec.1 A
307 Requirements related to stability (intact and damaged) are
given in Sec.6 for ULS condition
and Sec.8 for ALS condition.Sec.1
A 400 Classification
Sec.1 A
401 Classification principles, procedures and applicable class
notations related to classification services of offshore units are
specified in the DNV Offshore Service Specifications given in Table
A1.Sec.1 A
| Table A1 DNV Offshore
Service Specifications |
| Reference | Title | DNV-OSS-101 | Rules for Classification of Offshore Drilling
and Support Units | | DNV-OSS-102 | Rules for Classification of Floating Production,
Storage and Loading Units | | DNV-OSS-103 | Rules for Classification of LNG/LPG
Floating Production and Storage Units or Installations | | | Rules for Planning and Execution of Marine
Operations | |
Sec.1 A
402 It shall be agreed with DNV, at the start of the project,
what documents from the project Master Document Register (MDR) shall
be the subject of approval. Documentation for classification shall be in accordance with
the NPS DocReq (DNV Nauticus Production System for documentation
requirements) and DNV-RP-A201.
Sec.1 A
403 It is possible to limit the classification to a selected scope
(e.g. HULL, TOPSIDE, DRILLING MODULE, ACCOMMODATION etc,). Details
of the scope for classification shall be discussed and agreed with
DNV at the start of the project.
Sec.1 A
404 Some of the design phases (e.g. hull and deck mating, transportation,
installation and decommissioning) presented in the standard are
not covered by normal classification scope, Technical requirements
given in DNV-OS-C101 Sec.8, related to Serviceability Limit States,
are not mandatory as part of classification.
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