11-DNV-2.7-3-portable-offshore-units[1].pdf

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DNV 2.7-3Portable Offshore Units

Subsea Lifting OperationsKranTeknisk Forening

Per ystein Alvr

Stavanger, 28 November 2007


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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 (June2006)

Describing what will be updated in the next revision

Indicating application of 2.7-3 for subsea


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International Regulations

IMOs MSC/Circ.860 Guidelines for the approval ofoffshore 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 thecompetent authority or by organizations Duly authorized bythe Administration

states that offshore containers should be inspected annually

Refers to other standards for detail requirements, those listedare DNV 2.7-1, DNV 2.7-2, EN 12079 and BS 7072 (withdrawn)


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Why 2.7-3?

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

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

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


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Definition

Portable Offshore Units

Definition in SfC 2.7-3: Portable Unit or package with a maximum grossweight not exceeding 50 tonnes , for repeated or single use with aprimary service function, handled in open seas, to, from or betweenfixed 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


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Content in 2.7-3

GENERALScopeDefinitionsList of symbolsDocuments for approval and informationNational authoritiesReferences

CERTIFICATION PROCEDURESIntroductionDesign ReviewTesting and inspectionCertification of existing uni tsMaintenance of certificateSummary of procedures

DESIGNStructural strengthWeldingDesign detailsUnits with tanksMaterialsPrototype Testing

MANUFACTUREGeneralWeldingSecondary structureProduction documentation

Production testingMARKINGSafety markingIdentification markings

Addi tional information markings (optional )

Other markingINFORMATION PLATESGeneralOperational limitationsInformation plateInspection plate

OPERATIONAL RESTRICTIONS

PERIODIC EXAMINATION, TESTS AND REPAIRSGeneralInspection, test and repairs on uni ts


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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


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Procedure for Certification

Application sent to DNV.

Order confirmed and fees agreed.

Drawings, documentation and calculations reviewed and approval givenby the approval office.

Prototype offshore Unit manufactured under supervision of the Society'sSurveyor.

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

Production proceeds according to the agreed Quality Plan orManufacturing Survey Arrangement. Production tests according to list inSection 4.5.

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


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Design Requirements - General

Design to promote means for safe handling and transportation.

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

Acceptable stress, structural displacement and stiffness.

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

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

All Units in compliance with this Standard for Certification shall beevaluated with regard to the risk of uncontrolled skidding and overturningon a moving ship deck.

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


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Design - Structural Strength

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

Allowable Stresses . Von Mises equivalent stresses, e = 0.85C. 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

Cosn

F RSF

=

SKL Sling angle


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Pad Eyes- Not outside unit- Dim requirements: D hole < R padeye_pl Tpadeye > 75% Shackle inside width

- Strength: Req. to combined stress on net areaOther 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


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Materials and Manufacture

Design temperature, normally -20 C

Steel quality requirements

Aluminium and other materialsWelding Qualification

Inspection of Welds

Secondary structure

Production documentation


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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: Spreaderframe is required!


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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.- DNVs Inspector Stamp (Ref. 4.4).- Operational restrictions (if any).

Inspection PlateThe InternationalConvention for SafeContainers, CSC


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The need for stricter operational restrictionsThe need for stricter operational restrictionsthan the general restrictionthan the general restriction Hs = 6.0mHs = 6.0m forforthe offshore lift shall be evaluated.the offshore lift shall be evaluated.

Limitations of sea state for the transportLimitations of sea state for the transport

event could be applicable.event could be applicable. A specially arranged procedure or A specially arranged procedure orarrangements for handling or sea fasteningarrangements for handling or sea fasteningcould be required.could be required.

It is advised that an agreement on theIt is advised that an agreement on thepossible operational restrictions ispossible operational restrictions isestablished with DNV in an early stage ofestablished 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 thatunfortunately is rather unclear, but it generally says:


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Plans for Next Revision Slide 1

Improve the definition of the border between 2.7-1 and 2.7-3 includinglimitations 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 todo this. One proposal is to categorize the units into, say 3 classes withlift limitations at 6m (as 2.7-1), 4m and 2.5m . The categorization shouldbe based on the design (i.e. type A, B, C or D), single or multiple useand weight.

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

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

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


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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 beconsidered 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.


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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 & optionalimpact 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)


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Subsea Design Factor, Lift

Design factor structure: 3.0 (2.8) This covers DAF and LF

Additional 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 strictoperational limitations the drag area and volume, including addedvolume/mass should be reasonably limited.

The revised 2.7-3 will include some guidance on how to obtain an unit thatdo 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


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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 ofdamage 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, asindicated in the list below, will be included.


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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 applicableoperation limitations based on the actual installation vessel and procedure.

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

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


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11-DNV-2.7-3-portable-offshore-units[1].pdf

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