Stress Analysis of Piping Inside Insulation 2

[simplemath]

Hi, all.
When reviewing stress analysis of tank piping in the annular space filled with perlite insulation,
I found it hard to evaluate the load from perlite insulation.

The piping is located between inner tank and outer tank.
I would assume two loads from perlite:
1. dead weight porportional to depth;
2. friction due to pipe thermal move.

Load 1 is staightforward.
But how about load 2 ?
Do not know how to justfy it.
No clue about how to calculate either.

Pipe is 12" SS.
Crogenic service.
Has certain length both in horizental run and riser.
Perlite pressure to tank wall is 150psf.

Thanks

 

[BigInch]

For behavior of piping embedded in compact granular materials, you can get some ideas here,

http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1522&context=jtrp

and at this link you will find how to analyze pipe embedded in soil,

http://www.pipestress.com/Pages/PEpapers.html

Then it becomes a matter of determining the appropriate values for perlite. I don't know what those might be, but you might be able to find some values for clean sand (Ottawa sand) and extrapolate to some values for perlite that will give you conservative results.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[simplemath]

Thanks Biginch.

I downloaded the paper “stress analysis method for underground pipe lines” from the website. It really clarify me on how to calculated friction force of buried horizontal line.

However, it does not suggest a way to deal with friction of riser pipe, which is the major part of tank annular space piping.

In this respect, one consultant engineer suggests the following equation:
Riser friction = density of perlite X hydraulic radius of tank

Where hydraulic radius of tank = Cross section of tank annular/”wetted “perimeter

The equation yields reasonable result. But I do not know the theoretical basis for it.

A further clarification will be highly appreciated.

 

[BigInch]

I'm not understanding the configuration of the riser and how it fits in the tank space. Can you post or link to a picture or a diagram?

I also do not have any knowledge of that formula. Maybe if I can see a diagram of your installation, I could propose something else.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[LSThill]

meanstone (Aeronautics)

COADE Mechanical Engineering News Buried Pipe Analysis, Nov 1988*

http://coade.com/company_newsletter.asp

Design Guideline for Buried Steel Pipe

This guideline presents design provisions for use in evaluating the integrity of buried pipelines for a range of applied loads. Both new and existing welded buried pipe of carbon or alloy steel fabricated to ASTM or API material specifications and constructed in accordance with ASME B31 pressure piping codes are considered. The following load conditions are addressed: internal pressure, vertical earth loads, surface live loads, surface impact loads, buoyancy, thermal expansion, relative pipe-soil displacement, movement at pipe bends, mine subsidence, earthquake ground motion, effect of nearby blasting, fluid transients, and in-service relocation. The ASME B31 Guideline Committee currently is considering integrating the ALA-developed guidance into its standard.

http://www.americanlifelinesalliance.org/

Guidelines for the Design of Buried Steel Pipe buried_pipe3

L S THILL

 

[simplemath]

The tank is double-wall double dome tank with perlite filled in between to provide insulation. Riser starts from inner tank dome , goes down inside the perlite-occupied annular space and penetrate outer tank shell at bottom to joint with process piping.
Will draw a sketch later.

 

[BigInch]

I'd use a friction factor x depth of perlite x density of perlite. After a certain number of temperature contractions and expansions of the interior tank, the perlite should compact and begin to develop frictional resistance. Check the stress with say 1/3 of that resistance for tank cycles that occur before full compaction is reached, then check it with the full frictional resistance. For any lateral movements of pipe use the active-passive pressure calculation methods of soil mechanics, similar to the way they are used in retaining wall design.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[simplemath]

BigInch, my question is how to include into the load case combination the load that calculated by "friction factor x depth of perlite x density of perlite" ?

Any perlite load on the riser piping?


It boils down to simple math.

 

[BigInch]

I envision it as similar to a hydrostatic load calculation, but X a friction factor of perlite on the steel pipe riser. Alternate expansions and contractions of the tank sould compact the perlite around the riser enough such that friction from contact with the compacted perlite will arise.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com