piping connected to pig receivers

[clooney]

Hi Gents,
Suppose I have an Underground oil pipeline which is anchored (with an anchor block) just before coming out of the soil. The Above-ground portion is directly connected to a "pig receiver" which I am told has a fixed saddle.

I am not comfortable with this arrangement because the portion of the pipe restrained between the pig receiver at one end and Underground Anchor block at the other end will exert extremely large loads on the pig receiver/fixed saddle and on the Anchor block when undergoing thermal expansion (suppose at Start Up when exposed to solar radiation in summer time). I am told by our senior engineers that this pipe arrangement is typical of lines leading to and from pig receivers and pig launchers and I have also seen corresponding schematics showing this pipe arrangement in older oil pipe line design books.

Anyhow, the Anchor block can always be designed for larger loads; my main concern is the internal axial load developed in the pipe itself which is eventually exerted on the pig receiver and its fixed saddle.

Please, note that the segment of the pipe between the two abovementioned points has a longitudinal profile the shape of a skewed or horizontally stretched "S" (no fittings, elbows, and reducers used; the pipe is bent).

Can't really play with making the above ground piping more flexible either because adding loops will translate into using elbows which will interfere with the pig travelling inside the pipe.
I hope I got my point across.

Any Ideas? Apparently this layout has worked before but when actually doing the calculations to find out what the loads on the pig receiver are like, I end up with very large loads (on the order of 30 metric-tons axial load).

Any input on this topic is highly appreciated.

C

 

[Hookem]

Soil is not rigid; rather, it is a sem-solid liquid, per my college professor. When pushed upon, it moves, albiet almost impercetably, yet, it moves. In fact, most footings, foundations, etc. have designs that are not based on strains and stresses as we spend so much time learning, but rather on restricting the amount of movement. Who cares if an entire foundation (all everything attached to it) moves, as long as it moves uniformly. We only worry if there is differential settlement. Same thing with pipeline L&R's. In fact, the properly sized thrust block will move significantly less than the above-ground barrel support.

My only additional input to you would be to slot the holes on the support saddle to allow for thermals (daytime to nighttime, summer to winter, fluid flowing vs non-flowing, etc.).

 

[Elvie]

Clooney,
the pig receivers are usually designed with sliding saddles the oblong slots allowing full thermal expansion.

 

[clooney]

Elvie,
If "slot holes" are used for the saddle, then I rest my case. I still haven't seen the manufacturer's dwgs of this specific pig receiver. I found an older drawing but the detail of the saddles resting/sliding on conrete pedestals is not shown.
I asked around 5-6 people in our office, they either didn't know or they guessed that one of the 2 saddles supporting the pig receiver must be fully fixed to resist the pressure thrust induced by the pig moving through the pipe line and nearing the inlet of the barrel. However, the barrel does have a Relief valve into atmosphere.
By the way, aren't you most likely going to have a "cylinder of slug flow" being pushed thru the piping and entering the barrel of the receiver at a relatively high velocity?
Perhaps, the slot holes in the sliding saddles, are just long enough to ONLY allow for thermal expansion but restrain the receiver's movement under any impact loading. I think, this makes sense.
thanks again,
C

 

[clooney]

hookem,
thanks for your input. Most likely my sources in the office are not correct about the saddle being fully anchored. like I told 'Elvie', I still haven't seen any relevent drawings but slot holes will certainly change everything.
thanks,
C

 

[77mccoy]

Loosen up your anchors change your default from 7,000,000
lbs a inche to 100,00 watsch what happens