Droped object study

Truong Dinh Hieu-PVE

Risk Assessment

Dropped Objected at Platform

THE PURPOSE OF THIS SLIDE


I. DROPPED OBJECT AT PLATFORM

The crane lift object such as: container, pipe reel, drill riser, basket and other.

All object could be dropped and impacted pipeline.


1. METHOD RICK ASSESSMENT

Failure Frequency due to Dropped Object will be checked with DNV OS F101.

i.e.

Frequency of accidental loads as table blow:


2 INPUT DATA Pipe data. Number of Lifts Per Year of Crane

(if available). Water Depth at platform. Drawing of pipeline approach at

platform. Breadth of dropped object (if available). Data of protection (ex. Gravel Cover depth,

Gravel Diameter, Bearing Capacity Coefficients, Structure

Protection Energy )


3 METHODOLOGY1. Angel deviation of object

2. Drop probability due to crane activity (flift) selected in table 9

3. Probability of dropped object landing within any one ring.

4. The probability of hit to a pipeline or umbilical with within a certain ring, r..


3 METHODOLOGY Ar = Area within the ring

Lsp = Length of subsea line within the ring based onthe figure of riser approach.

5. The frequency of hit can be estimated based on the number of lifts, the drop frequency per lift and the probability of hit to the exposed sections of the subsea lines. For a certain ring around the drop point.

Nlift = number of lifts assumed as table below

Overall annual risk of any dropped object impacting on pipeline


3 METHODOLOGY6. The shape of dropped objects will be different impacted the

pipeline, that impact energies are different. The range and probabilities of impact energies is show in Table below:

7. Accumulated Hit Frequency for different Impact Energy Levels(i.e each object category hit (impact) pipeline can be given different frequency probabilities.

8. Total Energy Absorbed

E other see table 8 DNV RP F107


3 METHODOLOGY

Impact Energies for given dent sizes. i.e the pipe deformation 5%,10%.. need energies is:

Energy absorbed by the gravel dump and natural backfill: Dropped object is tubule object: For other than non-tubular objects, like containers.The bearing capacity coefficients can be chosen as Nq = 99 and Nγ = 137. The effective unit weight γ’ is assumed to be 11 kN/m3. sγ is a shape factor equal to 0.6, and L is the length of the impacting side, z = penetration depth, Ap = plugged area of the falling pipe ,

Energy absorbed by concrete coating X0 : assumed as concrete coating thickness With each pipe deformation need total energy

absorbed ex. As table side:Dent depth, % Energy Required, kJ5 63.62 10 90.50 15 125.31 20 166.54 25 213.30


3 METHODOLOGY9. Each energy absorbed must be calculated frequency of impact

to make pipe deformation 5%, 10%..

10. Probability of Damage and Release based on dent diameter. i.e.

Condition Probability see table below: Calculation Probability of Damage. Note : Damage due to D1 is not considered

to give damage leading to failure. The failure frequency is obtained by adding the results for damage class D2 and D3. i.e.

Dent Depth Impact Frequency5 4.95E-0610 1.29E-0615 1.12E-0620 7.72E-0725 5.57E-06


Calculation Probability of Release. Note : release due to R0 is not considered to give release as defined in section 4.2 DNV RP F107 . The failure frequency is obtained by adding the results for damage class D2 and D3. i.e.

Failure Frequency due to Dropped Object will be checked with DNV OS F101. i.e.

11. Question 1 : Method of protected if DAMAGE_RESULT is FAIL ??????? Protect Frame Concrete mattress Concrete Sleeper Lids

3 METHODOLOGY


II. DROPPED ANCHOR ALONG ROUTE

Shipping activity could be required to cast anchor (cross/along pipeline route)

Anchor can be impact directly on top of the pipeline or dropped vicinity the pipeline route can be drag

http://www.youtube.com/watch?v=wwaVD2KqitM&feature=related http://www.youtube.com/watch?v=9gmZXzmGNg0&feature=related http://www.youtube.com/watch?v=okKGTPA-470&feature=related

http://www.youtube.com/watch?v=9gmZXzmGNg0&feature=related


II. DROPPED ANCHOR ALONG ROUTEDropped Anchor from Shipping Activity along

Pipeline Route

Anchor Impact Directed Pipeline


A. Input Data Anchor Dimension Pipe Data External diameter, wall thickness, concrete coating Concrete Cube Strength,(DNV F107-The cube strength varies typical from 35

to 45 MPa) fcu (NOTE: specification concrete coating) Environment Data Water Depth Hydrodynamic data(density of seawater, …)

..

1. ANCHOR IMPACT


1. ANCHOR IMPACT

B. Methodology based old project. (NOTED)

1) Impact energy

m: mass of anchor at impact position. Vt : Terminal Velocity at impact position. Question 2: What is Terminal Velocity ? Terminal Velocity is found when the object is in balance with respect to

gravitation forces, displaced volume and flow resistance. i.e. The object fall with a constant velocity. Following DNV RP F017, after approximately 50-100 meters, a sinking object will usually have reached its terminal velocity. A question this here as “what happen before 50 meter”.

Terminal Velocity is defined as below method:• The object falling with low speeds and faster

every second until object reaches a terminal velocity (due to drag force resisting and Buoyancy effects ).


1. ANCHOR IMPACT Based on defined above and Newton II law the velocity can be:

i.e. The velocity at all position can be calculated as: For dropped object scenarios, results of the risk assessment are not

normally very sensitive to an absolutely “correct” capacity assessment. Therefore variety of impact energy is estimated within ± 20% will normally

give acceptable variations in the resulting risk level. i.e. Ek = E. ± 20% 2) Following DNV RP F107: x0: Penetration depth of object into coating Y: Crushing strength of the concreteb: Is the breadth of the impacting object,h: The depthD: Pipeline diameter


C. Discussion Question 3 :Which criteria using to check damage impact ? i.e. how many

penetration depth of anchor into coating is damage /safety ? Note : a methodology will be added to check pipe deformation of anchor into

pipe steel (dent depth). E assumed as =50%( or 60%) Ek

Percent of Pipe deformation and pipe diameter will calculated form E.q 3 (side) will be checked with 5% i.e. if (δ/D <5% ,“Minor Damage”, “Major damage”)

1. ANCHOR IMPACT


2. ANCHOR DRAGGING

A. Input Data Anchor data Weight anchor Fluke length Shank width Angle between fluke and shank Soil Data Fiction angle if sand Clay


B. Methodology Each type different anchor (fluke length, weight ) will be given anchor

penetration into different soil layer based on figure below: The anchor drop vicinity pipeline route can be drag anchor, that will be avoid

as propose burial pipeline. The minimum burial depth requirement to avoid anchor

dragging CL : Clearance Proposed is assumed 0.5m

2. ANCHOR DRAGGING


2. ANCHOR DRAGGING

C. Discussion Based on analysis in methodology section, the burial depth is required all the

route (Actual, the pipeline just burial in shore approach section). Question 4: The shore approach section will be buried to avoid effect wave,

reduced concrete thickness , anchor drop/drag and trawl gear. Will other section be buried? Why not

Cost buried What method to protect pipeline to avoid damage due to anchor drop/drag

outside shore approach section?(ex. Have 10 ship line busy crossing route pipeline )

Droped object study

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