DNV 2.7-3
DNV 2.7-3
Portable Offshore Units
Portable Offshore Units
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Subsubseea Lifta Lifting ing OOperaperatiotionsns
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KranTenTekniknisksk ForForeneninging
Per Øystein Alvær
Per Øystein Alvær
Stavanger, 28 November 2007
2.7-3?
2.7-3?
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What is DNV Standard for Certification 2.7-3?
What is DNV Standard for Certification 2.7-3?
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How should 2.7-3 be used?
How should 2.7-3 be used?
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Clarifying why 2.7-3 has been issued
Clarifying why 2.7-3 has been issued
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Giving a general overview of the content in 2.7-3 (June
Giving a general overview of the content in 2.7-3 (June
2006)
2006)
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Describing what will be updated in the next revision
Describing what will be updated in the next revision
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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
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 customers
have 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
Definition
Portable Offshore Units
Definition 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 2.7-3
GENERAL Scope Definitions List of symbols
Documents fo r approval and inf ormation National author ities
References
CERTIFICATION PROCEDURES Introduction
Design Review
Testing and insp ection
Certification of existing uni ts Maintenance of certificate Summary of proc edures DESIGN Structural strength Welding Design details Units wi th tanks Materials Prototype Testing MANUFACTURE General Welding
Secondary struct ure
Production documentation Production testing
MARKING Safety marking
Identification markings
Ad di ti onal inf or mati on mar ki ng s (o pti onal ) Other markin g
INFORMATION PLA TES General
Operational limitations Information plate
Inspection plate
OPERATIONAL RESTRICTIONS
PERIODIC EXAMINATION, TESTS AND REPAIRS General
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
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
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.
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 ν Cos n F RSF × − × = 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
Materials and Manufacture
Design temperature, normally -20º C Steel quality requirements
Aluminium and other materials Welding Qualification
Inspection of Welds Secondary structure
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
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 Plate
The International Convention for Safe Containers, CSC
The need for stricter operational restrictionsThe need for stricter operational restrictions
than the general restriction
than the general restriction Hs = 6.0mHs = 6.0m forfor the 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 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 theIt 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
Plans for Next Revision – Slide 2
Tables showing test lift weights will be revised/corrected.
Weld type requirements and some manufacturing requirements to be
reviewed.
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 – 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 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
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 inclination Maximum water depth
Allowable loads on tugger points and guiding systems Sling 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.
