When is a system considered to be cyclic in the water, oil & gas industries?
What makes it a cyclic pressure rated system, is it the pumps used?
If it is the pumps, which pumps?
How does it compare with statically rated systems?

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Request for Question Clarification by pafalafa-ga on 23 Feb 2004 08:14 PST

I'm not sure I fully understand your question.  

Cyclic pumps are indeed used in the water, oil and gas industries, and
in other industrial applications.

Are you basically asking "what is a cyclic pump"?  If so, I can
probably answer your question.

But if you are looking for some other sort of information, could you
please clarify what it is you need.

Thanks a lot.

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Clarification of Question by karbiz-ga on 24 Feb 2004 03:59 PST

I am doing some research, if you have access to ASTM 2992, or API15LR,
those are industry standards for fiberglass pipe. In them they specify
that pipes should be cyclically rated or statically rated. (I.e tested
under cyclic loading or static loading). Static being pressure held,
cyclic: fluctuating pressure. I am trying to find out whether the
cyclic requirement comes from the pumps being used or due to valve
opening and closing in the system? I.e is it the diaphram, positive
displacement or centrifugal pumps which are creating this... if it is
diaphram... are they still in common use in the industry?

I am trying to understand the cause of cyclic rated piping (what it
means and when is it considered to be a cyclic system?)

NB: I think that cyclic rating should be disregarded, since it was
probably based on older technology, and that manufacturers should be
able to go with only statically rated pipe... I need evidence to
support this argument.

Karbiz and researchers --

I'd be careful on the assumptions that cyclic rating is obsolete.  My
experience is in pressurized aircraft, where the number of
pressurization-depressurization cycles is EXTREMELY important in
determining the life of the fuselage.  It is the cycling that produces
stress and metal fatigue.

The most-notable example was the structural failure of the DeHaviland
Comet, the first-generation of pressurized jet aircraft.  The story's
detailed here"
Smithsonian Magazine
"The Comet's Tale" (Pushkar,June, 2002)
http://www.smithsonianmag.si.edu/smithsonian/issues02/jun02/pdf/smithsonian_june_2002_comets_tale.pdf

Of particular interest to you Karbiz should be the method by which
they tested the pressure cycling: use of water to flood the fuselage
and simulate pressure cycles.

Best regards,

Omnivorous-GA

I believe it is the pressures rising and falling or building up in a
cyclic nature and falling again due to valves and pumps forcing liquid
into a flow inside the pipe line. contact Pembina Pipe in Drayton
Valley Alberta Canada or Drayton Valley chamber of commerce For there
address or email address, they are a company that moves oil thru there
pipelines for oil companies, they know pipe!

Identifying and anticipating cyclic pressure is of critical interest
in the design and fabrication of indutrial fluid power systems, aka
hydraulic and pneumatic systems. These are systems of pumps, valves
(directional control as well as flow and pressure control), and
actuators: linear (cylinders) and rotary (motors), and fluid
conductors - pipe, tube, etc.

The cyclic pressure concerns in these systems are caused by the very
pronounced changes in pressure levels that are inherent in their
normal operation. The system will see increasing pressure as work is
performed, then reduced pressure as the system goes to "neutral";
further, pressure will spike significantly as an actuator hits its
load (although well designed systems will minimize this), and spikes
occur when actuators reach the end of their stroke or arc, the
severity of which will be a function of the speed at which pressure
relief or other controls respond.

In normal duty modern hydraulic systems will encounter pressure cycles
ranging between 0 to 15,000 psi (0 to 1,000 bar); pneumatic systems
generally range from 0 to 250 psi (0 to 17 bar).

These values make it obvious that research and proper selection of
pipe and other fluid conductors, as well as the system operating
components, require close attention.

Details on test protocals are in National Fluid Power Association
standard NFPA/T2.6.1-1974 category 2/90.

Regards

absoluterated