dnv 2.7-3 - portableoffshoreunits - subsealiftingops

DNV 2.7-3 Portable Offshore Units

Subsea Lifting OperationsKranTeknisk Forening

Per ystein Alvr DNV Marine OperationsStavanger, 2 December 2010

Det Norske Veritas AS. All rights reserved Slide 226 November 2010

Content of this Presentation

DNV Standard for Certification 2.7-3, March 2011- Relationship DNV 2.7-1 & DNV 2.7-3- Define what is a DNV 2.7-3 Portable Offshore Unit?- Brief overview of content

Subsea use of PO Units- Design condition/loads- Considerations- Operational aspects

Design load calculations- Background for design factors- Example on how to calculate the lift design factor

Lift rigging design


Relationship with DNV 2.7-1

The design of offshore containers are regulated through:IMOs MSC/Circ.860 Guidelines for the approval of offshore containers handled in open seas

Only offshore units/containers certified according to DNV Standard for Certification 2.7-1, Offshore Containers will automatically fulfil the guidelines in MSC/Circ.860.

DNV 2.7-3 does not apply for units that are defined as offshore containers. Offshore containers shall be designed, manufactured and certified according to DNV 2.7-1.

What is DNV 2.7-3 if it is not an offshore container?


Definition - PO Units Definition in DNV 2.7-3: A PO Unit (Portable Offshore Unit) is a

package or unit intended for repeated or single offshore transportation and installation/lifting.

The maximum gross mass should normally not exceed 100 tonnes.

Could be lifted subsea!

5 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 Type E, generally defined


Content in DNV 2.7-3 GENERAL Scope Design & Operation Definitions Documents for acceptance and

information National authorities References

CERTIFICATION PROCEDURES Introduction Design Verification Certification testing and inspection Summary of procedures

DESIGN Design conditions Materials Operational Class Analysis and Acceptance Criteria Design Loads, Lifting & Impact Sea Transport Lifting Points Design details PO Units with tanks Subsea application

MANUFACTURE General Materials Welding & NDE Secondary structure - Coating Production documentation

TESTING Extent - Lifting - Impact - Production

MARKING Operational Class & Safety marking Identification markings Information plates Additional information markings (optional)

LIFTING SETS PERIODIC EXAMINATION, TESTS AND REPAIRS General Inspection, test and repairs on units

Appendix Padeye design


Test to Define Appropriate Design Basis

Tests to define the PO Units Operation Class & design notations

Container shaped & W


Procedure for Certification

Application sent to DNV (e.g. to [email protected]).

Order confirmed and fees agreed.

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

(Prototype) PO 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.

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


Materials and Manufacture

Design temperature, normally -20 C

Steel quality requirements

Aluminium and other materials

Welding Qualification

Inspection of Welds

Secondary structure

Production documentation


Testing Requirements All point lifting test

- Mandatory, could be omitted for single transports

- Test load mnimum of 2.5 x MGW & F

2-point Lifting- Needed for R60, R45 & R60-SE - Test load minimum of:

- 1.5 x MGW, and- 0.6 x F

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

less for MGW > 25tTest conclusion: Spreader frame is required!

NOT PA

SSED

NOT PA

SSED

NOT PA

SSED

NOT PA

SSED

NOT PA

SSED

NOT PA

SSED


Marking Operational Class and Safety Marking

Identification by Certificate number Information Plate

- Type of PO Unit and Operational Class- Name of manufacturer.- Month/year of manufacture.- Maximum gross weight (kg) - ......- ......

Inspection Plate- .- .

DNV 2.7-3 R45-Subsea-SEMGW = 16300 kg

OPERATIONAL RESTRICTIONS





Design load calculations- Background for design factors- Example on how to calculate the lift design factor

Lift rigging design


Subsea Design Condition

The effective weight of a PO Unit and the dynamic amplification factor will vary during a subsea lift. The calculation of maximum effective weight shall include possible trapped water (when lifted out of water) and possible suction when lifted from the sea bottom.

The worst realistic combination of effective and dynamic amplification shall be considered. Normally it is considered adequate to use the following combination as basis for the design condition:- DAF = 2.0- Submerged weight is 0.9 x MGW- General design factor = 1.4

The applied design condition always needs to be verified againstthe actual installation condition.


Subsea Design Factor, Lift

Design factor structure:

Additional factor for padeyes as for lift in air:

The following design requirement are 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.

Hence DNV 2.7-3 include the following guidance:

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

MGWFSub = 5.21.2 and SKL


Subsea Design Loads

Effect of horizontal wave loads. The tilt effect of this on the PO Unit could normally be considered covered by the requirements in 3.5.

Local design for hydrodynamic loads, e.g. slamming loads.

Tugger points for horizontal and rotational control.

Guiding system for final positioning.

Retrieval loads.

Hydrostatic pressure.

Additional loads that should be considered for PO Units for subsea use:


Design Considerations

Functional requirements, e.g. installation aids, as defined by contract specifications, etc.

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

Lift points below CoG should normally be avoided.

Proper draining when lifted out of the water (if applicable).

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

Extended (more than a few days) subsea application of PO Units should be specially evaluated and shall not be considered covered by the given requirements in this standard.


Subsea Operational Aspects

All assumed operational limitations shall be clearly indicated in the PO Units design documentation. Critical limitations should be indicated in the certificate and normally marked on the PO Unit. Such limitations 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, tag/tugger line connection points, skids for monitoring systems/equipment, should be installed as agreed.





Design load calculations- Background for design factors- Design factors

Lift rigging design


Design Loads Lifting - Background

Based on 2.7-1 and adjusted to new VMO Standard

Constant (with mass) design factor not considered adequate due to:- Rigging not mandatory, hence no direct influence on padeye design- Required minimum thicknesses reduced from 2.7-3 June 2006- Full penetration welds not mandatory in 2.7-3

Variation in operational limitations considered adequate due to:- PO Units could be many different design solutions- Normally PO Units do fulfil all the requirements in DNV 2.7-1. to minimize

handling risk.- Weight variations greater than for DNV 2.7-1 containers- Use frequency variations greater than for DNV 2.7-1 containers

If offshore lift operational wave height limit has to be taken less than in DNV 2.7-1 (i.e. Hs = 6.0 m) why not also reduce the design requirement?


PO Units - Operational Class

PO Units shall be assigned to a Operational Class for the offshore lift. The class should be selected based on the following: - Weight.- Risk evaluation.- Type of structure, A through E

Risk based on items as - Equipment specially sensitive to impact loads - Out sticking parts - Lack of roof protection - Lift points in positions where they could be damaged by impacts - Lack of proper crash framing and there is installed/ transported equipment that could be damaged due to impacts - exceptionally geometry or unhandy (big) size - Lift rigging including (loose) spreader bar(s)


Operational Classes

The following three Operational Classes with operational limiting significant wave height as indicated are used in this certification note for DNV 2.7-3 PO Units:

- Class R60 Lift from/to vessel in max Hs = 6.0m- Class R45 Lift from/to vessel in max Hs = 4.5m- Class R30 Lift from/to vessel in max Hs = 3.0m

In addition the following notations will be used:- PO Unit for Subsea use: Subsea- PO Unit for single event/transport only: SE


Safety Factor Calibration


Design Requirements - Summary Calculation Methods. Only the primary structure shall be included in the

design calculations.

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

Sea Transport loads- According to calculated accelerations or based on 1g

Design Lifting Loads:- All point lift structure- 2 point lift structure (for some structures)- Padeyes all point lift (with SKL factor) only

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

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


Design Loads All points Lifting

For 2-point lift: 0.6 x F for the structure.


Design Load Lift Points

For 2-, 3- or 4 leg sling arrangements without spreader bars, the resultant sling force (RSF) on each padeye should be calculated based on the following equation:

RSF = 1.2 x SKL x PL x F / cos() = the angle between the sling leg and vertical.

SKL = Skew load factor due to sling length deviations. Could be taken as 1.25 (assuming that sling lengths are adequately controlled) for a 4 slings rigging and 1.1 for 2- and 3 slings riggings.

PL = Per cent Loading of F (quasi-static calculations) in the most loaded padeye.


Lift Point, Out-of-Plane Loads

Design angle between sling- and padeye plate planes.

Inaccuracies in padeye fabrication and rigging design considered (e.g. due to hook size) causing an angle between sling and padeye plate planes.

Angle difference between crane hoist line and the line from the hook centre to the PO Unit CoG. This could be due to: - Inclined transport vessel deck during lift-

off.- Not plumb hoist line during lift-off.- Horizontal loads on PO Unit from e.g.

tugger lines and impacts.- If subsea PO Unit, horizontal loads from

waves (and current).


Appendix A - Padeyes

Equations given to check: - Bearing pressure- Tear out- Cheek plate welds

at the padeye hole

In addition- Combined stress

has to be checked for critical sections including connection to main structure





Design load calculations- Background for design factors- Design factors

Lift rigging design


Slings & Shackles

For Slings:

MBL 1.6 x RSFTable 7-1 Minimum Sling Diameter (D)

Class Single event Multiple use

R30 D 10 mm D 12 mm

R45 D 12 mm D 15 mm

R60 D 14 mm D 18 mm

For Shackles:

WLL 0.4 x RSFand MBL min 5 x WLL


DNV 2.7-3 Portable Offshore UnitsContent of this PresentationRelationship with DNV 2.7-1Definition - PO UnitsContent in DNV 2.7-3Test to Define Appropriate Design BasisProcedure for CertificationMaterials and ManufactureTesting RequirementsMarkingContent of this PresentationSubsea Design ConditionSubsea Design Factor, LiftSubsea Design LoadsDesign ConsiderationsSubsea Operational AspectsContent of this PresentationDesign Loads Lifting - BackgroundPO Units - Operational ClassOperational ClassesSafety Factor CalibrationDesign Requirements - Summary Design Loads All points LiftingDesign Load Lift PointsLift Point, Out-of-Plane LoadsAppendix A - Padeyes Content of this PresentationSlings & Shackles