Transportation Loading Stresses

[Angsi2]

Equipment: Div 1 Pressure Vessel, vertical orientation, 108" ID, 15' T/T, 4' skirt height, 0.5" shell wall thickness.
Transportation Mode: Land via truck, transported horizontally with two wooden temporary shipping saddles.


Question: Specification requires a prespecified transportation acceleration forces in all Fx(1.5g), Fy (1.25g) and Fz(1.25g) directions to be considered. Will I be correct to proceed in the following manner?

1. The acceleration forces brought to act at the COG of the vertical vessel transported in horizontal position i.e. Fx, Fy, Fz added to the empty weight of vessel at the COG
2. Temporary saddles are checked to see if they could withstand these forces
3. Zick stress analysis checked with the above loads to confirm no overstresses

Please advise and thanks in advance.

 

[austsa]

My comments are from my experience only - not necessarily good or best practice engineering .....
I've never seen or done transport calcs when using wooden saddles. I find it hard to imagine how (2) can be done (other than tying down the vessel onto the saddles and pulling/pushing - something that I would not recommend). Also would not have thought that you can conduct Zick analysis and get any meaningful results using wooden saddles (as attachment is not "secure").
There are many variables when using wooden saddles - choice of soft/hard wood, how saddle is fabricated, etc. IMO wooden saddles can be used when based on engineer's "judgement", it will be acceptable. Judgement is based on experience, vessel size/weight, distance to destination, road conditions, etc.

 

[gr2vessels]

austsa is correct, the transport loads act only when welded supports of vessel are used (saddles or skirt) for deck anchoring. There is nothing to be over stressed at any transport acceleration on a 15 ft vessel clamped on transport saddles, unless is free fall over the cliff...
Cheers,
gr2vessels

 

[Angsi2]

Thanks for the input. The acceleration forces are, as you may already be aware, are derived from the transport motions. As such regardless of the method used to secure or the type of the shipping saddles, these loads n doubt exist and needs to be accounted for. Further additional loads 'may' be imposed by pretensioning of the straps, etc or anything that is holding the vessel down but these laods could be negligible in comparison to the acceleration/decceleration factors and will not be part of this discussion.

IMO: The acceleration forces will act at the shipping saddles and its design needs to be verified for that. These loads will be over and above that of the vessel weight. Secondly, since the the vertical vessel is being shipped in a horizontal position, zick stress analysis will be required to check the stresses at the shells, horns of the saddles etc., while taking into account the acceleration forces acting at the COG of the vessel.

 

[jtseng123]

Tell the truck driver don't corner too fast, and slowly start and stop. I heard vessel flying out of deck during cornering.
Everything can be checked, regardless wood or steel. Steel is simple. For wood, nail down more, and wood has its typical strength that can be found and check. Stress on shell, you can still use Zick. Yes, assuming g load is acting at COG. All X, Y, Z loads to be considered acting simutaniously. If you hit a pothole or bump, you will have +/- vertical load. Don't forget loads can be either direction.
Tie wire or strap is to be designed for vertical up or down aceeleration so it will not snap.
Note, wood is not as stable as steel, so use wider wood base (longitudinal direction) than typical steel wear plate.
One more thing, wood saddle may not be cheaper than steel.
I have reviwed hundreds of shipping saddle calcs and designs for all kinds of shipping modes. If you are the fabricator, you do need to produce calc and dwg for your customer to review. Not tough, but tedious.