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DNV 2.7-3 Portable Offshore Units

Subsea Lifting OperationsKranTeknisk Forening

Per Øystein AlværStavanger, 28 November 2007

© Det Norske Veritas AS. All rights reserved Slide 223 November 2007

2.7-3? What is that?

The intention of this lecture is to briefly answer:• What is DNV Standard for Certification 2.7-3?

• How should 2.7-3 be used?

This is done by:• Clarifying why 2.7-3 has been issued

• Giving a general overview of the content in 2.7-3 (June 2006)

• Describing what will be updated in the next revision

• Indicating application of 2.7-3 for subsea


International Regulations

IMO’s MSC/Circ.860 “Guidelines for the approval of offshore containers handled in open seas”

proposed to IMO by Norway

states that the International Convention for Safe Containers (CSC) does not cover Offshore Containers

states that offshore containers should be approved by the “competent authority” or by organizations “Duly authorized by the Administration”

states that offshore containers should be inspected annually

Refers to other standards for detail requirements, those listed are DNV 2.7-1, DNV 2.7-2, EN 12079 and BS 7072 (withdrawn)


Why 2.7-3?

Experience has shown that Standard for Certification No 2.7-1 "Offshore Containers”, is being used more and more in the industry today than ever before. As a consequence of this increased demand, DNV customershave voiced a strong requirement for a need to certify portable offshore Units that are not shaped like containers, according to Standard for Certification No 2.7-1.

As a result of this market demand Standard for Certification No 2.7-3 has been developed, which covers all other types of portable offshore Units, other than offshore containers. DNV firmly believes that this new standard will meet the customers need for these services and at the same time enable DNV to expand in this market segment.

This new Standard has been developed in close co-operation with the update of the Standard for Certification No 2.7-1.


Definition

Portable Offshore UnitsDefinition in SfC 2.7-3: Portable Unit or package with a maximum gross weight not exceeding 50 tonnes, for repeated or single use with a primary service function, handled in open seas, to, from or between fixed and/or floating offshore installations and ships.

Also: Could be lifted subsea!

4 types defined:- Type A, skids arranged with crash frames- Type B, skids without crash frames- Type C, no dedicated skid frame- Type D, stress skin design


Content in 2.7-3GENERALScopeDefinitionsList of symbolsDocuments for approval and informationNational authoritiesReferences

CERTIFICATION PROCEDURESIntroductionDesign ReviewTesting and inspectionCertification of existing unitsMaintenance of certificateSummary of procedures

DESIGNStructural strength WeldingDesign detailsUnits with tanksMaterialsPrototype Testing

MANUFACTUREGeneralWeldingSecondary structureProduction documentationProduction testing

MARKINGSafety marking Identification markingsAdditional information markings (optional)Other marking

INFORMATION PLATESGeneralOperational limitationsInformation plateInspection plate

OPERATIONAL RESTRICTIONSPERIODIC EXAMINATION, TESTS AND REPAIRSGeneralInspection, test and repairs on units


Test if SfC 2.7-3 is applicable

Tests to define type A, B, C or D

Integrated service? Use 2.7-2

Container shaped & W<25t? Use 2.7-1

Tank for dangerous goods? IMDG Code + 2.7-1

W < 50t? VMO-Rules

X


Procedure for Certification

Application sent to DNV.

Order confirmed and fees agreed.

Drawings, documentation and calculations reviewed and approval given by the approval office.

Prototype offshore Unit manufactured under supervision of the Society's Surveyor.

Unit tested according to prototype test requirements, witnessed by the Society's Surveyor.

Production proceeds according to the agreed Quality Plan or Manufacturing Survey Arrangement. Production tests according to list in Section 4.5.

DNV surveyor issues Portable Offshore Unit Certificate (form 49.06a) and affixes emblem.


Design Requirements - General

Design to promote means for safe handling and transportation.

Selected criteria to cover a transportation event involving sea voyage and lifting offshore.

Acceptable stress, structural displacement and stiffness.

Units designed for dynamic forces generated when handled in a sea state of up to Hs = 6m, unless otherwise stated in operational limitations.

Units intended for repeated transportation events and to be mixed with other frequent handled goods shall be free from protruding parts outside the envelope of the Unit.

All Units in compliance with this Standard for Certification shall be evaluated with regard to the risk of uncontrolled skidding and overturning on a moving ship deck.

Consider type A, B, C or D as defined in section 1.1.


Design - Structural Strength

Calculation Methods. Only the primary structure shall be included in the design calculations.

Allowable Stresses. Von Mises equivalent stresses, σe = 0.85×C. For steel: C = Re = minimum yield stress.

Design Lifting Loads:- Primary structure: F = 2.5 x MGW x g

- pad eye: Single padeye: RSF = 2 x F

Impact Loads:- Horizontal impact - Vertical impact (Drop test)- Minimum thicknesses

Welding- Red. factor: Fillet = 0.5, partial = 0.75 and full pen. = 1.0

)()1(2.1

νCosnFRSF

×−×

=

SKL Sling angle


Pad Eyes- Not outside unit- Dim requirements: Dhole < Rpadeye_pl Tpadeye > 75% Shackle inside width- Strength: Req. to combined stress on net area

Other details:- ISO-corner Castings- Drainage- Fork Lift Pockets- Walls- Equipment and Supports for equipment- Lashing- Tugger points- Doors and hatches- Coating and Corrosion Protection

Design Details


Materials and Manufacture

Design temperature, normally -20º C

Steel quality requirements

Aluminium and other materials

Welding Qualification

Inspection of Welds

Secondary structure

Production documentation


Testing Requirements

All point lifting test- Mandatory, maybe omitted for single

transports- Test load: 2.5 x MGW

2-point Lifting- DNV decide if necessary- May not pass calculations- Test load: 1.5 x MGW

Vertical Impact Test- Drop or lowering test- Could be substituted by calculations

less for MGW > 25t

less for MGW > 25t

Test conclusion: Spreader frame is required!


Marking

Safety marking

Identification by Certificate number

Information Plate- Name of manufacturer.- Month/year of manufacture.- Manufacturer's serial number.- Maximum gross weight (kg) at design sling angle.- Design temperature.- DNV’s Inspector Stamp (Ref. 4.4).- Operational restrictions (if any).

Inspection PlateThe International Convention for Safe Containers, CSC


The need for stricter operational restrictions The need for stricter operational restrictions than the general restriction than the general restriction Hs = 6.0mHs = 6.0m for for the offshore lift shall be evaluated. the offshore lift shall be evaluated.

Limitations of sea state for the transport Limitations of sea state for the transport event could be applicable.event could be applicable.

A specially arranged procedure or A specially arranged procedure or arrangements for handling or sea fastening arrangements for handling or sea fastening could be required. could be required.

It is advised that an agreement on the It is advised that an agreement on the possible operational restrictions is possible operational restrictions is established with DNV in an early stage of established with DNV in an early stage of the enterprise. the enterprise.

Operational restrictions

Section 7 in SfC (Standard for Certification) 2.7-3 include a text that unfortunately is rather unclear, but it generally says:


Plans for Next Revision – Slide 1

Improve the definition of the “border” between 2.7-1 and 2.7-3 including limitations for units that can be certified according to 2.7-3.

It should be made mandatory to define clearly (upper) operation limitations. The revised CN shall include (specific) guidance on how to do this. One proposal is to categorize the units into, say 3 classes with lift limitations at 6m (as 2.7-1), 4m and 2.5m. The categorization should be based on the design (i.e. type A, B, C or D), single or multiple use and weight.

For (very) special units it should be stated that a handling procedure both for sea transport and offshore lift should be made and presented for review.

Criteria for sea transport are vaguely described. Design requirements for the transport to be included.

Design and documentation requirements to lifting sets should be included (at least) as an option.


Plans for Next Revision – Slide 2

Tables showing test lift weights will be revised/corrected.

Weld type requirements and some manufacturing requirements to bereviewed.

2.7-1 includes several appendices with useful information. It will be considered to include something similar in 2.7-3.

Include, as for 2.7-1, a tailor made certificate form.

Description of DNV 2.7-3 emblem, as for 2.7-1, to be included.

Several typing errors and incorrect references will be corrected.


Next Revision: Chapter 3 – Design“Chapter 3 – Design” will be considerably updated, e.g.:

- The general “design factor” - 2.5 for lift, will be a function of, op. lim. Hs, weight and subsea or not.

- Specific design requirements for transport will be included, normally 1g

- Accept criteria for stress and stability to be clarified.

- Deflection accept criteria to be deleted/updated (clarified why).

- Recommendations for vertical impact calculations.

- Minimum thickness requirement – modify considering weight & optional impact test.

- Padeye design criteria – Clarify/update and include 2.7-1 formulae as option.

- Clarify requirements to equipment and equipment supports

- Lashing and tugger points – rewrite requirements

- Include more guidance on when 2-point lift test & impact test are required.

- Subsea use (next slide)


Subsea – Design Factor, Lift

Design factor structure: 3.0 (2.8) This covers DAF and LFAdditional factor for padeyes as for lift in air

The following design requirements will be included to cover subsea:

In order to ensure that the unit could be installed without too strict operational limitations the drag area and volume, including added volume/mass should be reasonably limited.

The revised 2.7-3 will include some guidance on how to obtain an unit that do not need any special procedures to be installed.

The recommendations will be further reviewed, but will be something like:

A/Ws < 1.0 where A is drag area and Ws is the submerged weight

V/Ws < 2.0 where V is the volume of the unit + added (water) mass


Subsea – Design Considerations

All air filled members shall be designed for the maximum hydrostatic pressure, or proper ventilation/water filling shall be ensured.

Placing of lift points below CoG is normally not acceptable.

Lift point should be placed/designed in such a way that the risk of damage and/or accidental release of rigging is neglectable.

Effect of horizontal wave loads. (tilt of object in splash zone).

Local design for slamming loads.

Tugger points for horizontal and rotational control.

Guiding system for final positioning.

Retrieval loads, if applicable.

A set of additional (for subsea) design considerations, as indicated in the list below, will be included.


Subsea – Operational Aspects

All assumed operational limitations shall be clearly marked on the unit. This could be:

Installation wave height/periods (if evaluated/applicable)Special considerations, e.g. pass splash zone with inclinationMaximum water depth Allowable loads on tugger points and guiding systemsSling angles

The installation contractor needs to do a final assessment of the applicable operation limitations based on the actual installation vessel and –procedure.

Installation means on the unit, e.g. as marking, ROV grab bars, skids for monitoring systems/equipment, should be installed as agreed.

A set of additional (for subsea) operational aspects, as indicated in the list below, will be included.


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