DNV 2.7 3 Portable Offshore Units Overview

DNV 2.7-3 Portable Offshore Units Subs ubse ea Lifting Lift ing Opera peratio tions ns KranTe Kra nTekni knisk sk For Foren ening ing Per Øystein Alvær 

Stavanger, 28 November 2007

2.7-3? What is that? The inte int ention nti on of o f this t his lect lecture ure is to t o brie br iefl fly y answ answe er: • What is DNV Standard for Certification 2.7-3? • How should 2.7-3 be used?

This hi s is done don e 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Refers to other standards for detail requirements, those listed are DNV 2.7-1, DNV 2.7-2, EN 12079 and BS 7072 (withdrawn)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 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 update of the Standard for Certification No 2.7-1.

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 Desig n 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



Inspection, test and repairs on uni ts

Test if SfC 2.7-3 is applicable W < 50t? VMO-Rules Tank for dangerous goods? IMDG Code + 2.7-1

X

Container shaped & W 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



Production documentation

Testing Requirements 

 All point lifting test - Mandatory, maybe omitted for single

transports - Test load: 2.5 x MGW

less for MGW > 25t

Test conclusion: Spreader frame is required! 

2-point Lifting - DNV decide if necessary - May not pass

calculations

- Test load: 1.5 x MGW

less for MGW > 25t 

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

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

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

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



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





 A specially arranged procedure or arrangements for handling or sea fastening could be required. It is advised that an agreement on the possible operational restrictions is established with DNV in an early stage of the enterprise.

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 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 use (next slide)

Subsea – Design Factor, Lift The following design requirements will be included to cover subsea:

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

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

 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.

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

 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.

http://webshop.dnv.com/global/  1

2

3

4