Pillar connection weld detail

Discussion in 'Class Societies' started by Maritimer, Jan 20, 2017.

  1. Maritimer
    Joined: Jul 2007
    Posts: 29
    Likes: 2, Points: 0, Legacy Rep: 58
    Location: Canada

    Maritimer Junior Member

    I am working on a new project using Lloyd's Register and I have been using DNV for the past while. I am looking at the weld detail for connection of pipe pillars to the deck. In DNV this can be fillet welds but from what I see in Lloyds it needs to be a full penetration weld? Can anyone provide guidance on this? I think FP weld is excessive for the the connection of a pillar in compression.

    I must be reading the table wrong................
     
    Last edited: Jan 23, 2017
  2. NavArc...
    Joined: Nov 2016
    Posts: 16
    Likes: 1, Points: 3, Legacy Rep: 10
    Location: United Kingdom

    NavArc... Junior Member

    I think you're right.. for a pillar with tubular end connection it requires a full pen weld
     
  3. Maritimer
    Joined: Jul 2007
    Posts: 29
    Likes: 2, Points: 0, Legacy Rep: 58
    Location: Canada

    Maritimer Junior Member

    Lloyds Register pillar weld ridiculous

    Why would LR require a full pen weld here? The other classification societies don't. I looked at a few and they all appear to allow fillet weld connections. This pillar weld requirement seems out of balance with what they allow for other critical weld areas in the vessel.

    So the next part of the question, I have a circular base plate (doubler) on the bottom of the pillar of about 1.5 times the pillar wall thickness and 50 mm bigger diameter than the outside of the pillar (typical detail), do I need to have a full pen weld of the pillar to the base plate and then a weld of equivalent strength to the full pen weld for the base plate to the deck. If it is a strength issue that's what would make sense. (but doesn't make sense)

    Some have indicated that the pillar to base plate needs to be full pen weld and that the base plate to deck weld can be just a small fillet weld. That does not make sense to me. The full pen weld requirement is ridiculous, LR must have some old rule of thumb reason not tied to strength.

    Anyone have a LR approved typical detail for a pillar deck connection with welding details?
     
  4. TANSL
    Joined: Sep 2011
    Posts: 4,130
    Likes: 60, Points: 58, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    "The full pen weld requirement is ridiculous ....". Why you sai that?. Are you talking about full penetration or continuous welding. It seems to me to remember that, for example, all CS force, when the pillar is tubular (hollow), that the welding is continuous (not full penetration) to prevent moisture from entering the interior.
     
  5. Maritimer
    Joined: Jul 2007
    Posts: 29
    Likes: 2, Points: 0, Legacy Rep: 58
    Location: Canada

    Maritimer Junior Member

    Agree all welding needs to be continuous. Typically I would use continuous fillet welds.

    LR is requiring a complete penetration joint weld (full penetration). This weld requires edge preparation (bevels) on the pillar and then many passes of weld to provide a full welded connection of the complete pipe wall thickness. This takes more fabrication time for bevels and all the weld passes, requires welders that can do a one sided full penetration weld (usually pipe fitters ticket), and then NDE and rework are more of a concern.

    Only looking at pillars in compression and not located in tanks.
     
  6. TANSL
    Joined: Sep 2011
    Posts: 4,130
    Likes: 60, Points: 58, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    I corrected my previous post because the allusion to pillars in tanks was not correct. The hollow pillars are strictly prohibited inside the tanks.
    I did not look in Lloyd's rules but frankly, I do not know how you can get a full penetration into a tubular pillar. How to access the inner face to clean the root cord and weld ?. Should you place a backing plate and weld with inert gas? It seems very complicated.
     
  7. Ad Hoc
    Joined: Oct 2008
    Posts: 5,274
    Likes: 198, Points: 63, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Because a simple fillet weld there is no guarantee of transmitting the applied load. Measuring the leg length of the weld does not provide any evidence, other than its size, whether the weld has fused and provides the necessary throat thickness consistently, and that's the key, consistently, around the circumference of the joint. Without such a guarantee, how is the assumed end fixity of the strength of the joint confirmed..?....impossible.

    Thus having a full penetration weld ensures that the fused joint - throat thickness - has sufficient area to transmit the loads and also provide the end fixity for the strength calculations.

    Nope and it is a strength issue. But not how you are thinking it. The structural joint of a pillar to a face plate is very different from the structural joint of a doubler to a face plate. The load path is very different ergo - different minimum requirements.
     
  8. Barry
    Joined: Mar 2002
    Posts: 768
    Likes: 22, Points: 18, Legacy Rep: 158

    Barry Senior Member

    Attached are some drawings of different welding combinations and one which shows a vertical bevel being welded to a flat plate

    http://www.free-ed.net/free-ed/Cour...uction/050205 Welding/Welding00.asp?iNum=0302

    Full penetration welds from one side are not unusual as many hundreds of thousands of such joints appear in pipeways from low pressures to high pressures conditions

    The bevel on one side is important for complete melting of the pipe but what is extremely important to ensure that the bottom plate has full weld penetration is the "root spacing" between a top beveled pipe and the flat plate. IE you have to raise the bevel root from the flat plate to ensure plate penetration

    Inner access to the weld is not required
     
  9. TANSL
    Joined: Sep 2011
    Posts: 4,130
    Likes: 60, Points: 58, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Barry, I have read with interest the file in your link. I have not seen anything new or anything that speaks about the case that we are dealing with. I have seen "T" welds and pipe welds that have nothing to do with welding pillars to face plate.
    By the way, something similar, but more complete, can be found in all regulations of the different Classification Societies.
    In my previous post I talked about the welding with backing plate to achieve a full penetration but with the condition of welding with inert gas to avoid having to clean the root. This is possible but I have never seen it on ships.
    Thank you for trying to clarify this matter, but I insist on clarifying that I have never spoken of welding between pipes.
     
  10. Barry
    Joined: Mar 2002
    Posts: 768
    Likes: 22, Points: 18, Legacy Rep: 158

    Barry Senior Member


    Tansl
    In the first post that I have quoted above you asked a very specific question "I do not know how to get full penetration on a tubular pillar"
    I responded by giving you a link but should have referenced Figure 3.9, lower right hand quadrant.
    You will see a straight bevel as well as a radius that goes to the root, This enables better filler and vertical member mixing when welding. It also shows a root spacing to ensure that the entire vertical member and the flat plate gets penetrated. It is not complicated.

    Yes, in your second quote above, I referenced one side welded, not backed, pipeway butt connections only because there are millions of them made without backing and have stood the test of time but more importantly have stood non-destructive x-ray inspection as to the quality of the weld. They are not complicated

    The OP asked a straight forward question as to what he believes to be an excessive requirement for a full penetrating weld on a column that is subject, at least in his understanding of the loading, to ONLY COMPRESSIVE FORCES that might be able to be covered by a fillet weld.
    I am guessing here of course but I suspect then the OP thinks that by stabilizing the column from moving laterally, you should not need an FP weld

    Ad hoc replied that an FP weld will probably guarantee that the weld will be strong enough to carry any load that may exist or could exist that the column could be placed under.
    This is obviously correct. (Adhoc, I did not quote you precisely but this is what I took you to mean)

    Without seeing the actual designed pillar and loadings, I have to guess at a few things but because there is a pillar whose primary function is to resist a compression load, this might not be the only load that the column might be subjected to.

    Long slender columns can bend/buckle even at pure axial loaded conditions and produce bending stresses in the column.
    Euler derived an equation to determine a critical load based on the area moment of inertia, length and material type.
    You can google Critical Loads in Columns, or Buckling Considerations in Columns, for the theory behind this

    In columns that are not long and slender but where the loads are non concentric, this loading will induce tension bending stresses in the column

    In situations where ONLY axial loading is not guaranteed, such as a where the structure is flexing causing loading not to be concentric, such as a ship, the critical load will be much lower than a pure axial, concentric load. In the event of a failure, maybe brought on by a grounding, you might want the column to provide more load carrying capability than pure compression.

    The full penetration weld would be one way to ensure that any tension stresses caused by bending/deflection would be able to be carried by the welding and an FP is the easiest way to accomplish this.
     
  11. TANSL
    Joined: Sep 2011
    Posts: 4,130
    Likes: 60, Points: 58, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Barry,
    Yes, you're right, my sentence "I do not know how to get full penetration on a tubular pillar" does not make sense because I say later how can I get it, as my interpretation is that if you can not sanitize the root of the welding, you can not speak of full penetration.
    Regarding everything else that you explain, thank you, really. I think it has nothing to do with what I'm talking about, but it's just my opinion. I also think that welding schedule depends on the stress to be transmitted, regardless of how it is generated.
    On the other hand, I'm surprised that only Lloyd's Register is asking for full penetration into pillars. If I have not misunderstood it, I think that can not be so.
    Thanks again, Barry.
     
  12. jehardiman
    Joined: Aug 2004
    Posts: 2,263
    Likes: 160, Points: 63, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    There is part if your issue: while the stanchion (pillar) may as a unit may be in compression, the end fixity of the head and heel are not in compression for all cases (i.e. there is a moment across the plane of the weld surface so a tension on one side and a compression on the other...think of a tween deck stanchion with an overhung deck load during stowing). A PT1S weld will act as a crack starter, allowing for failure of the weld due to cyclic loading and should never be used in structural welds subject to tension. A T1J or T1V with or without backing bar will not have this problem and can support tension loads up to 1/2 yield strength.
     
  13. Maritimer
    Joined: Jul 2007
    Posts: 29
    Likes: 2, Points: 0, Legacy Rep: 58
    Location: Canada

    Maritimer Junior Member

    To follow up on this post.

    - The pillars are only in compression. An FEA analysis of vessel was completed and loads on pillars were reported as part of the analysis.
    - LR is the only Class that I have checked that has the requirement for full pen weld of pillar connection. I checked DNVGL, BV, and RINA. DNVGL will even allow fillet welds in tension on pillars with a special calculation.

    I have attached a sketch of the LR approved connection detail. I did not include in original format as the client may not like that.

    I have typically worked to DNV and have not had this FP weld requirement before. The FP weld is many more passes of welding and requires a bevel edge preparation and good welders to get the root pass.

    I suspect LR may be concerned that there is a GAP between the pillar and the base plate that is then covered up by a fillet weld so that the load in the pillar is not transmitted through the pipe wall thickness to the base plate and deck but only through the shear area between the fillet weld and the pillar. A FP weld makes this impossible. If a gap between the pillar and the base plate was present a fillet weld could fail under loading or allowing cracking that then allows moisture into the hollow section to cause corrosion issues leading to failure. To counter this I would propose a hold point for Class inspection on pillar welds but there is no allowance for this from LR. Pillar to base plate is to be a FP weld. Hard to complete a FP weld in a 12.5 WT pipe and then only see a 5 mm fillet weld hold the base plate to the deck.

    So be it.....weld it up!
     

    Attached Files:


  14. oataru
    Joined: Nov 2010
    Posts: 8
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Thailand

    oataru Junior Member

    I am reading LR ship rule, Part 3, Ch. 10., Sec.2, Table 10.2.1, and unfortunately tubuar pillar end conneciton requires FP as you are complaining.
    And, it seems you are aware of the background already.
    Since base plate can transmit the compressive force from pillar to the deck directly, 5 mm fillet weld on base plate is good enough just to hold the structure in-plane. It all makes sense.

    Agree that some other Classes do not have this FP requirement. For example, GL only asks for fillet weld with 0.4 factor.
     
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.