Stress analysis of jacketed pipes

[nikolastrojman]

Hi

I've received a remark from client of mine concerning the load case we didn't apparently took into account when we did stress analysis of jacketed pipes. In this remark it is stated that we only took operating case into account, but we failed to analyse the "start up case" (or starting conditions in which the system could operate for some period of time if I understood the remark correctly). Does anybody know what my client might be referring to? What starting conditions is he talking about?

By the way the stress analysis was done in Caesar II program.

 

[BigInch]

You should consider all possible pressure and temperature states, such as for example, during start-up in winter when temperatures may be in fact be lower than normal operating conditions, or even lower than what might be considered "normal ambient". For a pipe in pipe, that might represent an outside pipe temperature higher than the temperature of the inside pipe. Where as the normal operating condition might have a relatively cold outside pipe and a hot inside pipe.

I hate Windowz 8!!!!

 

[LittleInch]

Isn't there also a case where the pipe might be only half full of hot liquid in a cold pipe and this introduces some severe bending moments?



My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[nikolastrojman]

There is one thing I've forgot to mention which was in in the remark of my client. The client sad that these starting conditions actually refer to the outer pipe, which is hotter than the inner pipe (when it comes down to operating conditions). Also these jacketed pipes are located inside the building.

LittleInch can you elaborate more on your post. Or point me to the text which treats these problem.

Thnx

 

[LittleInch]

Can you describe your system a little better, such as size, temp of outside jacket, temp of inside.

Normally jacket is for when you needed to keep the inner pipe contents at a certain or minimum temperature.

Start up is difficult to see.



My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[nikolastrojman]

Well it is 3"/2" jacketed pipe system, with 80°C outside temperature and 70°C inside temperature.The inside medium is some kind of process fluid (density around 1300 kg/m3), and outside medium is hot water.

 

[DSB123]

Hope you have checked that the inner pipe can sustain the outer pressure if the inner pipe is empty or under vacuum if this is possible? Caesar will not check this for you.

 

[XL83NL]

Another important issue is to check for longitudinal forces/stresses, which may not be 'recognized' if you do not apply ASME B31.3 Appendix P.
This occurs when the inner pipe wants to pipe more than the outer one, or vice versa.

 

[DSB123]

XL83NL,
Please clarify your statement "This occurs when the inner pipe wants to pipe more than the outer one, or vice versa." as I am confused!!!!
I presume you mean "This occurs when the inner pipe wants to expand or contract more than the outer one, or vice versa.

 

[XL83NL]

@ DSB123; you got my typo there! My correct wording obviously should've been

This occurs when the inner pipe wants to expand or contract more than the outer one, or vice versa.

 

[LSThill]

[PDF] GOOD REFERENCE BOOK:
Sam Kannappan, P.E. - WordPress.com
pipestress.files.wordpress.com/.../introduction-to-pipe-stress-analysis-sam...‎
Introduction to pipe Stress analysis. ... another book entitled Advanced Pipe Stress Analysis by the same author ... Jacketed Pressure Piping System 160.

PRESSURE PIPING SYSTEMS
Method of Calculation Core Pipe Thickness page 160, 162

http://pipestress.files.wordpress.com/2011/12/introduction-to-pipe-stress-analysis-sam-kanappan.pdf

 

[LSThill]

[PDF] GOOD REFERENCE BOOK:
Sam Kannappan, P.E. - WordPress.com
pipestress.files.wordpress.com/.../introduction-to-pipe-stress-analysis-sam...‎
Introduction to pipe Stress analysis. ... another book entitled Advanced Pipe Stress Analysis by the same author ... Jacketed Pressure Piping System 160.

PRESSURE PIPING SYSTEMS
Method of Calculation Core Pipe Thickness page 160, 162

http://pipestress.files.wordpress.com/2011/12/introduction-to-pipe-stress-analysis-sam-kanappan.pdf

 

[pennpiper]

nikolastrojman wrote:
"There is one thing I've forgot to mention which was in in the remark of my client. The client said that the starting conditions actually refer to the outer pipe, which is hotter than the inner pipe (when it comes down to operating conditions)."

I think this statement is misleading.
In fact, if there is no fluid (or 70C fluid) in the inner pipe but the jacket has 80C fluid flowing then both pipes are seeing the same 80C temperature. The outer (Jacket) pipe will do doubt be insulated but it and the inner pipe will both be seeing the 80C temp on one surface and a reduced temp on the other surface.

prognosis: Lead or Lag

 

[MikeHalloran]

Standard bubble test pressure at the marine exhaust shop was 15 psi, representative of the typical seawater pressure within the jacketed pipes, which normally ranged from 3"/4" OD to 10"/12" OD.

Then we built some J-shaped pipes in 13"/14" OD for a go-fast boat powered by helicopter engines. Mirror-polished outside, with laser-cut internal baffles to keep the jacket flow distributed, nozzles projecting from the inside at the distal end to cool the exhaust gas coming out of the boat. We sold them for a fortune, and probably still lost money.

We got to build a second set when the builder fired 'er up and measured high backpressure.

The inner tube had collapsed almost completely during the jacket leak test.
The buckle was between the two elbows, so it was impossible to see without a mirror on a stick.
The entire shop heard a 'bang' during the test, but nobody thought anything of it, because stuff was always falling or being hammered on.

If we'd made the inner tube 12 gage instead of 14 gage it wouldn't have collapsed. I figured that out with some back calculations after the adventure.

(attachment shows similar pipe installed)

Mike Halloran
Pembroke Pines, FL, USA

 

[LSThill]

Flexibility Stress Equation

The axial stress was added to the flexibility stress equation. While axial stress in not important in most piping systems, it can be important for piping that is jacketed or buried. The 2010 edition required that it be considered, but it was not in the equation

http://becht.com/blog/changes-in-the-2012-edition-of-asme-b31-3

 

[XL83NL]

Leonard Stephen (r u a bot?) THill, Im not sure if it's appreciated to share copyright protected material ...

 

[DSB123]

XL83NL,
Spot-on !!!!! But thats always his "stock" answer or a lengthy bibliography of references. Never actually answers the question.