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DNV-OS-C102 Structural Design of Offshore Ships

Sec.2: cture and elements not covered by Rules for

SECTION 2
cture and elements not covered by Rules for

Sec.2
A. Introduction

Sec.2
A 100   General

Sec.2
B. Selection of Material

Sec.2
B 100   General

Sec.2
B 200   Design and service temperatures

Sec.2
B 300   Hull structure

In the Rules for Classification of Ships Pt.3 Ch.1 materials are categorized into Material Classes. The purpose of the structural categorization is to ensure adequate material and suitable inspection to avoid brittle fracture, and to ensure sufficient fracture resistance of a material (stress intensity factor) to avoid crack sizes which may develop into brittle fracture at certain stress situations.

Sec.2
B 400   Topside structure and elements not covered by Rules for Classification of Ships Pt.3 Ch.1

Guidance note:
The consequence of failure may be quantified in terms of residual strength of the structure when considering failure of the actual component.

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Sec.2 B

Table B1 Material Classes
Material class	Structural member	Equivalent structural category in the DNV-OS-C101
I	— Outfitting steel — Mezzanine decks, platforms — Pipe support structure — Laydown platforms — Doubler plates, closer plates and support infill steels in topside structures 1)	Secondary
II	— Stair towers — Topside modules (plate, web frame, girder) 2) — Main structures in riser hold — Longitudinal and transverse bulkheads in way of moonpool and setback area — Offshore Crane boom rest and main supporting structures
III	— Main girders and columns in truss work type modules — Topside support stools and main supporting structures — Pipe/riser rack stanchions — Main structures in drill-floor and substructure — Main supporting structures for helideck 3) — Crane pedestal (shipboard and offshore) — Flare tower — Foundations and main supporting structures of heavy machinery and equipment: e.g. thruster, gantry and rail, chain stoppers, offloading riser fairleads, anchor line fairleads, winches, davits, hawser brackets for shuttle tanker, towing brackets etc.	Primary
IV	— Deck and bottom corner plates in way of moonpool — Foundations and main supporting structures for derrick (substructure) — Foundations and main supporting structures for flare tower and offshore crane pedestal — Main supporting structures for turret	Special
To have the same minimum yield strength as the material to which they are attached Stiffener and other local members (brackets, collar plates, web stiffeners) are classified as Class I. For material selection of helideck and substructure, see DNV-OS-E401 Note: Main structures and main supporting structures are primary load bearing members such as plates, girders, web frames/bulkheads and pillars

Sec.2 B
404   Alternatively materials for the specific structural members specified in Table B1 may be selected based on equivalent structural category in accordance with the principles given in DNV-OS-C101.

Sec.2
C. Inspection Principles

Sec.2
C 100   General

Sec.2
C 200   Hull structure

Sec.2
C 300   Topside structure and elements not covered by hull structure requirements

Sec.2 C

Table C1 Inspection categories
Inspection Category	Material Class	Equivalent structural category in the DNV OS- standards
I	IV	Special
II	III	Primary
III	I, II	Secondary

Sec.2 C
303   The weld connection between two components shall be assigned inspection category according to the highest of the joined components. For stiffened plates, the weld connection between the plate and stiffener, stringer, and girder web to the plate may be inspected according to inspection category III.

Sec.2 C
304   If the fabrication quality is assessed by testing, or well known quality from previous experience, the extent of inspection required for elements within material class III may be reduced, but not less than for inspection category III.

Sec.2 C
305   Fatigue critical details within material class II or III shall be inspected according to requirements in inspection category I.

Sec.2 C
306   Welds in fatigue critical areas not accessible for inspection and repair during operation shall be inspected according to requirements in inspection category I.

Sec.2 C
307   The extent of NDT for welds in block joints and erection joints transverse to main stress direction shall not be less than for inspection category II.

Sec.2 C
308   Topside stools, or topside - hull connections, material class III, shall be inspected according to the requirements in inspection category I for the areas shown in Figure 1.

Sec.2 C
309   Inspection categories for offshore crane pedestals connection to deck are given in Figure 2.

Sec.2 C

	Where: Length 'a' to be 0.35l, minimum 120 mm 'a' does not need to be bigger than 500 mm
Fig. 1   Inspection categories for topside stool with soft nose brackets
Fig. 2   Inspection categories for offshore crane pedestal