Spring on Rollers? 1

[StressGuy]

Well, now I've seen everything. As of this posting, this bit is currently featured on the home page at PTP

http://www.pipingtech.com/

PT&P custom designed and fabricated these F-type variable springs with rollers to be used in a refinery in Kansas. The variables are fabricated from carbon steel with a stainless steel clamp-on shoe that attaches to the load column. These F-type variable spring assemblies measure 23" in height and have an upward travel of 3". The operating load is 1,000 lb. and the installed load is 1,300 lb. The function of this custom designed variable spring is to allow large axial movement along the axis of the pipe centerline. The load column is modified to accommodate the special clamp-on shoe. The customized wheels allow for movement of the entire spring assembly in conjuction with the pipe.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[jistre]

That's... intersesting.

If you're getting that much motion, why not put an expansion loop?

 

[bosse1950]

Interesting - looks by the pictures that the bearings on the rollers are completly exposed. This design looks like a high maintenance item with a limited life span. I'll give it 2 or 3 years until the wheel assemblies are corroded & frozen in place & the whole spring is scraping across the concrete floor (or contact surface)

 

[StressGuy]

But, I'm sure it works just fine in Caesar...

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[C2it]

It looks like part of an Ikea coffee table.

 

[BigInch]

Wheel axle shear, bearings exposed and no cotter pin on the nuts.

http://virtualpipeline.spaces.msn.com

"We can't solve problems by using the same kind of thinking we used when we created them." -Albert Einstein

 

[DSB123]

StressGuy,
They may well work fine in Caesar but you and I know that because Caesar results show things work does not mean that the actual physical implementation can be performed. You know things like "modelling" very small "gaps" and the like which provide acceptable results but cannot be constructed. Unfortunately there are a number of Stress Engineers who "model" things in Caesar which cannot physically be installed just to get the results they want.

 

[KernOily]

Well if nothing else you got to admit it's a creative solution. With a bit more thought, it might actually work. Sealed bearings, perhaps placing the casters in a track to control movement, etc.

I do some training on pipe stress. First thing I teach is that CII is nothing more than a really fast calculator and that it is REALLY good at GIGO.

There are all sorts of exmaples out there of items or systems that work great on paper but that can't be built. That's why you have senior-level design seminars in school: to hopefully get some exposure to what works in the real world, and what doesn't.

These are weird times in the oil patch, no?

 

[RossABQ]

Why wouldn't they just use polymer slide plates? Is the installer to align the casters in the expected direction of growth?

 

[jistre]

Well, RossABQ, polymer slide plates get dirty. They get gouged and cut, increasing their friction coefficients.

These nice open bearings and axles, however, solve all those problems!

I've got another failure mode for these things: Something ends up on the ground and chocks one of the casters. Anyone who's ever wheeled around a garage on a crawler knows that a small wheel comes equipped with a poorly understood fifth fundamental force of nature that attracts objects just barely over the critical height at which they will chock a wheel.

 

[xhpipe]

Far better to go for a rod hung can with adequate swing angle, just because somebody will sell you something does not mean you should always buy it.....

Regards,
XHPIPE

 

[StressGuy]

DSB123 - That was exactly my reason for sharing this.

Hopefully, this will be an eye opener to our up and coming stress folks that they need to ask the question "How are we going to do that" once they get that seemingly perfect arrangement of X, Y, and Z restraints in their model.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[JohnBreen]

Hmmmmmmmmmmmmmm,

Rube Goldburg LIVES!!!!!!!!!!!!!!!!!!!!

 

[JohnBreen]

This is interesting.

Actually I know of a power plant in Texas that has a Main Steam Piping system constant hanger attached to an overhead structure that rides on four three inch ball bearings within a "box" that limits its horizontal travel. The maintenance folks have been feeding the ball bearings white lithium disulfide grease on a regular basis for (so they say) thirty years. Inventive but of course not very practical - the ball bearings have worn-in a "track" now so those now define the real travel limit.

Then again that is Power Piping, B31.1 still includes the "........all pipe supporting elements SHALL be in accordance with the rules of MSS SP-58...." (paraphrased) and B31.3 simply references MSS SP-58 for figures that illustrate some types of acceptable supports/hangers.

Thanks to Ed for making Monday morning more interesting

Regards, John

 

[RossABQ]

John, I remember Grinnell Figure 170's being used extensively in coal-fired power plants ("horizontal traveller"). I also remember what happens when the enclosure fills with fly ash and the wheels/axles corrode.

The garage creeper analogy was what first came to my mind. They roll whichever direction the wheels are pointed.

 

[JohnBreen]

Hi Ross,

Yep, the olde Grinnell figure 170 is actually included in MSS SP-58. And yes, the same Texas power plant has some of those supporting the NPS 3 MS start-up steam to the BFW pump piping. However that plant is a natural gas fired (clean) plant. But they get almost as much "travel" due to hanger "swing" as they do from the rollers.

Regards, John.

 

[KernOily]

"I've got another failure mode for these things: Something ends up on the ground and chocks one of the casters. Anyone who's ever wheeled around a garage on a crawler knows that a small wheel comes equipped with a poorly understood fifth fundamental force of nature that attracts objects just barely over the critical height at which they will chock a wheel."

Hee hee. THIS, plus the subject photo, is exactly why one of my standard interview questions for potential engineering hires is "Do you work on your own car?" You wouldn't believe the looks and the replies I get... My experience is that a guy who knwos how to turn a wrench is pretty durn good in the design office as well... They don't turn out designs like Ed's picture