Dropped Object Study 4

[swtmoon]

Hi there,

Are there any one to help me about dropped object study?
Currently I should present about the Dropped Object Study
and I have few material.
It's not clear to me about followings;
1. Purpose of Dropped Object Study
2. Step by step method of Dropped Object Study
(I have one example, but I'm not sure this is all about)
3. What should we do with the result of dropped object study.

Please give me any informations or any text about the dropped object study.

Regards,

swtmoon

 

[mgp]

I'm not an expert on this but I know roughly what it is about.

Most offshore topsides have one or more cranes handling all sorts of things, e.g. loading containers off the supply vessel. Whenever the crane is handling any goods there is always a potential risk of dropping the item, whether it being due to the wire breaking or insufficient securement of the item to be lifted.

If such an object is lost (dropped) it may well cause severe damage to the platform - maybe even platform collapse or explosion due to process equipment being fractured.

The dropped objects study is an analysis to find out what happens to the platform and personnel safety if heavy items are dropped.

If the drop causes an undesirable accident/event, then protection must be provided by means of structures to absorb the impact.

You should redirect your question to the Structural engineering forum as the study and design is normally handled by these.

Hope this helps.

regards
Mogens

 

[StephenA]

The dropped object study also needs to look at any submarine pipelines that connect to the platform and what protection (if any) is required.

StephenA

 

[mgp]

Stephens comment just reminded me of a project I worked on where a production Jack-up was installed on a subsea (steel) storage tank.

In addition to looking at the subsea pipelines we also had to cover the top of the storage tank with grouting to protect the tank from falling objects, especially drill pipes being lost from the drill rig.

regards
Mogens

 

[LiamBlair]

dropped object analsysis is an important task to be taken particularly with reference to offshore pipelines. These pipes are designed with sometimes 4,5 or 6 coatings and are manufactured in a way to minimise heat loss so hydrocarbons do not cool and form solids which would subsequently block the line. Dropped objects can damage the coating, cause pentration of water into the coating substrate and encourage corrosion which would subsequently spread and cause major financial reprocussions at a later date (pipelines normally have design lifes of 25 years!). The indentation caused by a dropped object could also act as a 'stress raiser' just like a notch made in material testing, it would promote buckling at that point from thermal expansion,deep water pressure, pipe pressure etc etc etc.codes of practice do exist. see

"OTO 1995:959 An examination of the number and frequency of serious dropped object and swinging load incidents involving cranes and lifting devices on offshore installations for the period 1981-1992"

for further info. and most likely, codes and regulations.

 

[MetalMickey]

The dropped object study is an all too real design case that needs to be considered in subsea structures and pipelines. It highlights the probable impact loads that will be applied as a result of the dropped object.
If the water is deep enough object will reach terminal velocity.

Examples of impact energies are :

- Drill collar - 1050KJ
- BOP - 1290KJ
- Drill Casing - 164KJ

Hence they are substancial and need to be considered.

The main loads therefore are a result of :

- Kinetic Energy
- Momentum
- Mass and Velocity


The effect on the item can be calculated by a number of denting models for pipelines for example, i.e. based on the proportion of impact energy absorbed by local deformation of the pipe wall. General guidelines for UK sector can be found in HSE OTH561.

Hope this helps.