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# underground pipeline

## underground pipeline

(OP)
Does underground piping always require pipe stress analysis, even if it is an ambient pipeline?

### RE: underground pipeline

That depends on the Client, the project specification, and other conditions.  For example, a 2000 psi buried line would be a little dangerous, even at ambient.

Richard Ay

### RE: underground pipeline

Ambient is 100F in the summer and 0 in the winter.  That can be a lot of stress and even more force, if the area of steel is high, even without any pressure at all.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch
http://virtualpipeline.spaces.live.com/

### RE: underground pipeline

As Biginch point's out ambient conditions can vary. Use your experience and the physical conditions to which the pipe will be subject to determine if a formal stress analysis is required or if you are unsure engage a Company who can make a judgement based on the physical conditions to which the pipeline is subjected to.

### RE: underground pipeline

(OP)
Thanks for the advice, everyone.  The deciding factor for me was the fact that this installation will include booster pumps.  I'll need to do system stress analysis to give me the loads for the component analysis (API 610 nozzle loads).

### RE: underground pipeline

The rule of thumb I usually follow is this:

Take the specified minimum yield strength of the pipe in MPa and divide by six.  If the difference between installation temperature and operating temperature in degrees Celsius is greater than that, then not only is stress analysis mandatory, but you might find it difficult to "pass".

In other words:

For [(SMYS/6), MPa] < [(Th - Ti), C], stress analysis is mandatory

Regards,

SNORGY.

### RE: underground pipeline

SNORGY (Mechanical)

Please provice detail reference reqard to

For [(SMYS/6), MPa] < [(Th - Ti), C], stress analysis is mandatory

which reference book?

Leonard S. Thill

### RE: underground pipeline

LSThill,
SNORGY has already said it is a "Rule of Thumb" he utilises - maybe there is no reference to a book. Not everyone has a list of books but use judgement!!!

### RE: underground pipeline

It comes from algebraic rearrangement of the equations in CSA Z662 Clause 4 that relate to the maximum allowable combined longitudinal stresses.  It is at about that ratio, for a gas pipeline in a Class Location 1, that those equations begin to dominate over hoop stress towards computing the design wall thickness.

Regards,

SNORGY.

### RE: underground pipeline

Its obvious that is also very close to 0.9 SMYS - Hoop Stress Allowable in B31.4 & .8 Class 1, of 0.72, but I was too lazy to work out the relation to the axial compressive temperature stress at "Th-Ti,C" to see if the rule of thumb was actually valid IMO or not.  It certainly looked good enough to have a reasonable expectation of being true, which is all you really need for a "rule of thumb".

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch
http://virtualpipeline.spaces.live.com/

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