Pipelaying Barge Stability

Discussion in 'Stability' started by naserrishehri, Mar 6, 2019.

  1. naserrishehri
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    naserrishehri Senior Member

    Dear friends
    What stability criteria should be used to analyse stability for a pipe-laying barge?
    The attached picture shows type of related pipe-laying barge.
     

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  2. gonzo
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    gonzo Senior Member

    If you have to comply with a Class Society, that will give you the criteria? Is this for school?
     
  3. TANSL
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    TANSL Senior Member

  4. Dolfiman
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    Dolfiman Senior Member

    Your picture shows a conventional barge for S lay operations, S being the shape of the pipe from the welding stations on the barge to the final laying on the sea floor, via a stinger hinged at the rear part of the barge, which supports the upper part of the pipe S, and a lower free span down to the sea floor. The picture is the Damen 10129 barge on the model of Castoro 12 built for Saipem :
    https://products.damen.com/-/media/...-Barge/Pipe_Lay_Barge_YN551003_Castoro_DS.pdf

    As regard stability in general, Gonzo gives you the answer. But I presume your question is actually on the dynamic features of such barge, and especially the coupled heave-pitch behaviour, and its consequence on the bending and tension in the pipe. It is the key point, dynamic analysis are still in the research domain, here for example an academic paper on that subject.
    https://www.researchgate.net/publication/275090648_Numerical_Model_for_Pipeline_Laying_During_S-lay

    Practically, when the sea state is increasing, when the stinger and/or the pipe on its rollers begin to move significantly, it is time to lay down the pipe : the procedure is to weld a pipe head itself attached by a cable to the barge, to advance the barge on its mooring lines up to the full laying of this pipe head safely on the sea floor, then waiting for more manageable sea state to recover the pipe by a reverse operation. All this taking few hours, the key aspect is the anticipation, so an accurate meteo Ocean forecast and a knowledge (behaviour sensors + in situ numerical tool of analysis, ..) of the bending stresses in the pipe (free span in particular).
     
  5. TANSL
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    TANSL Senior Member

    And what about IMO stability criteria?. Shall we forget them?
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Stability is Statutory regulation. This means it is issued by the local Maritime authority where the vessel is operating.
    Tansl is correct on this.

    The technical specification must also list the criteria too.
    Otherwise how will the designer know if the vessel - as designed - is compliant or not?

    If the local Flag Authority does not wish to get involved (for whatever reason) it is often referred to Class for them to review and approve. But Class will only implement Statutory rules, ergo, your local maritime authority should provide your guidance, if your designer cannot.
     
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  7. naserrishehri
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    naserrishehri Senior Member

    In my case, I'm wondering why "GL" used criteria of MODU (Mobile offshore drilling unit) for the related pipe laying barge.
     
  8. RAraujo
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    RAraujo Naval Architect

    That will depend on the certification of the unit. Although not, technically, a MODU some Administrations (through national legislation) have been using MODU rules and applying them to other types of vessels (which can be designated by Mobile Offshore Units).
    Is GL acting on behalf of the Flag Administration?
    Which is the class notation?
     
  9. naserrishehri
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    naserrishehri Senior Member

    CLASS NOTATION:
    100A5 PONTOON EQUIPED FOR PIPE LAYING OPERATION ACCORDING TO OPERATION MANUAL
    MACHINERY: A-MC

    Is GL acting on behalf of the Flag Administration? YES.
     
  10. RAraujo
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    RAraujo Naval Architect

    Strictly from a Class point of view this is what their Rules say... Still missing the Flag interpretation
    upload_2019-3-11_11-42-11.png
    upload_2019-3-11_11-42-56.png
     
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  11. TANSL
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    TANSL Senior Member

    "Special considerations", must be taken into account because they can raise special cases, difficult to solve. Being "special", they are not defined and that is why you need to speak with the competent authority to establish them clearly.
     
  12. naserrishehri
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    naserrishehri Senior Member

    This is the criteria that the designer considered for pipe-lay barge.
     

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  13. TANSL
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    TANSL Senior Member

    Yes, that is the typical study when lifting weights with a crane on board, but it must be defined (the competent authority will do it), in what load condition it is carried out, the height of the weights as well as the longitudinal and transverse position of them. And, perhaps, some other special condition that the authority wants to check.
     
  14. naserrishehri
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    naserrishehri Senior Member

    In all loading conditions the same criteria has been applied.
     

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  15. TANSL
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    TANSL Senior Member

    Yes, of course, but in some loading conditions it may be harder to meet that criterion than in others. Therefore, the most unfavorable load condition should be studied to ensure that this criterion is met.
    You must also take into account the trim that occurs when lifting the weight.
     
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