Rules and Regulations For Classification of FOI

RULES AND REGULATIONS FOR THE
CLASSIFICATION OF A FLOATING OFFSHORE

INSTALLATION AT A FIXED LOCATION
PART 4 STEEL UNIT STRUCTURES
APRIL 2008
RULES AND REGULATIONS FOR THE CLASSIFICATION OF A FLOATING OFFSHORE INSTALLATION AT A FIXED LOCATION, April 2008
Ship Units Part 4, Chapter 4

Sections 2, 3 & 4
construction, survey and maintenance of the unit. 3.1.3 Structural components are normally grouped into
categories based on applied loading and stress levels, critical
2.1.2 Plans are to be submitted in triplicate, but generally load transfer points, stress concentrations and consequence
only one copy of supporting design documentation and of failure. Categories may be summarised as follows:
calculations is required. Plans and supporting documentation • Special: Structural elements in way of critical load trans-
should be submitted and approved prior to commencement fer points and stress concentrations;
of construction. • Primary: Elements essential to overall structural integrity;
• Secondary Elements where failure would be unlikely to
2.1.3 A copy of the Construction Booklet, Operations affect overall structural integrity.
Manual and In Service Inspection Plan must be submitted for See also Ch 2.4.
class approval, incorporating the final approved revisions of
relevant plans and documentation, see Pt 1, Ch 3, 1.6 and Pt 3.1.4 For an MDT above (i.e. warmer than) -5°C ship hull
3, Ch 1. material classes and steel grades should comply with Section
6.1 of the Common Structural Rules for Double Hull Oil
2.1.4 Full details of the documentation required are Tankers (CSR) and Pt 3, Ch 2 of the Rules for Ships, as
given in Section 3.2 of the Common Structural Rules for applicable. Material classes and steel grades for offshore
Double Hull Oil Tankers (CSR) and the relevant Parts of the related structural components (e.g. turret structures, process
Rules. Typical lists outlining required plans and equipment supports, etc.) should comply with Ch 2.
documentation are given in the following:
3.1.5 For an MDT below (i.e. colder than) -10°C material
Section 3.2. -- Common Structural Rules for Double Hull Oil classes and steel grades should comply with Ch 2.
Tankers (CSR)
Part 3, Chapter 1, Section 5, (Rules for Ships) -- Basic Hull 3.1.6 Material where the principle loads or welding
structure stresses are perpendicular to the plate thickness should have
Part 1, Chapter 3, Section 1.6. -- Planned survey programme suitable through thickness properties. The application of
Part 3, Chapter 1, Section 2. -- General, OIWS, Construction through-thickness property Z25 or Z35 grade material is
booklet required where tensile stresses exceed 50% of the Rule
Part 3, Chapter 3, Section 1.6. -- Production and oil storage permissable stress, with plate thickness in excess of 15mm. In
units (general) general Z25 grade would be required however for critical
Part 3, Chapter 3, Section 2.1. -- Production and oil storage joints Z35 will be required. For certain critical joints with a
units (structure) restricted load path this criteria would be subject to special
Part 3, Chapter 8, Section 1.11. -- Process plant facility consideration, for example mooring fairlead attachments and
Part 3, Chapter 9, Section 1.3. -- Dynamic positioning system anchor line or hawser connections.
Part 3, Chapter 10, Section 1.4. -- Positional mooring system
Part 4, Chapter 1, Section 4. -- General structure 3.1.7 Steel grades for special and primary structural
Part 4, Chapter 6, Section 5.2. -- Helideck components with thickness in excess of the limitations of Pt
Part 4, Chapter 7, Section 1.2. -- Watertight / weathertight 2, Ch 3 and Table 2.4.1 will be specially considered.
integrity
Part 8, Chapter 1, Section 3. -- Corrosion control 3.1.8 Where attachments/pads are located on special or
primary components subject to high stresses, the attachment
is to be the same material as the plating to which it is
attached, with welding to the same standard as the main
structure.
■ Section 3
Materials
3.1 General
■ Section 4
3.1.1 Steel should be manufactured and tested in Structural arrangement
accordance with Part 2 or other acceptable standards. The
strength and grades (notch toughness) of steel required will 4.1 General
depend on the following:
4.1.1 General requirements regarding location and
• Design temperature; separation of spaces, layout and arrangement of primary
• Thickness; structural components are given Pt 3, Ch 3,1.4. Detailed
• Substance being stored/processed; requirements given in Pt 4, Ch 9 and 10 of the Rules for Ships
• Structural category; together with Section 5 of the Common Structural Rules for
• Location. Double Hull Oil Tankers (CSR) are to be complied with as
applicable. See also 12.1.3.
3.1.2 The Minimum Design Temperature (MDT) should
be taken as the lowest daily mean temperature at the site 4.1.2 Overall subdivision of the hull should take full
based on a 100 year return period, see Pt 3, Ch 1, 4.4. account of strength and stability requirements and minimise
A design temperature of 0°C is generally acceptable for the consequences of damage, pollution risk and loss of the
determining steel grades for structure normally underwater. unit in the event of damage. Additional subdivision of the hull
2 LLOYD’S REGISTER

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RULES AND REGULATIONS FOR THE

CLASSIFICATION OF A FLOATING OFFSHORE

Ship Units Part 4, Chapter 4

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