Bolt preload in ASME VIII design-by-analysis

[james2007]

I am using 2007 ASME VIII part 5 (Design by Analysis) to perform a check on a design for a subsea clamp connector. The connector creates a seal and rigid link between two pipes using a preloaded heavy-duty bolt. Aside from the bolt preload, the unit undergoes pressure loads and bending moments.

My intention is to perform a full elastic-plastic analysis on the unit using a detailed finite element model. To do so I shall apply the appropriate loads to the model (as per Table 5.1) with appropriate load factors (as per Table 5.5 of part 5). The load factors stated in Table 5.5 do not seem to cover bolt preloads.

My question is this:

Do I have to apply the load factors in Table 5.5 to the bolt preload as well as the operational loads?

 

[gr2vessels]

james,
Very recently I have had discussions with "Vector" people, in regard with their subsea connectors / clamps. One of the questions was the preload on their bolts (Optima model). The info was declined as proprietary data and we been told that the purchased connector / clamp will have the precise number of turns on the bolt to achieve the seal. That means the bolt is never fully tensioned. That also means that the limiting factor must be in the clamp combined tensile and compressive stresses or in the pipe ends compressive stresses. Either way, it seems to me that the bolt itself is not really relevant in your stress analysis, particularly that you buy the connector with the bolt sized to suit the clamp and guaranteed by the clamp designer.
My two cents,
cheers,
gr2vessels

 

[james2007]

Thanks gr2vessels.

I agree, in my case the screw is not particularly relevant in the analysis either. But what I am concerned with is the influence of the bolt's preload on the plastic collapse of the clamp and whether ASME requires a load factor to be applied to this load.

I think this may be the case, as the sealing preload in the bolt might be considered a self-restraining loadcase (notation T in ASME VIII part5). Therefore according to Table 5.5 of 2007 ASME VIII a loadcase with a factor of 2.1 on all loads (including self-restraining load cases) should be analysed.

It would be good to know what people's views are on this kind of analysis.