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#107 - 06/08/00 11:49 AM Rigorous Analysis Guidelines
Mike Krawczyk Offline

Registered: 01/14/00
Posts: 1
As someone who does pipe stress work occasionally, but is extremely interested in the subject, I have had trouble finding an answer to the following question. Is there a set of guidelines that I could use, on a very large chemical plant piping job for instance, to cull out pipe runs that do not need analysis? I am familar with paragraph 319.4.1, but that seems very restrictive ( intermediate restraints...). Is there a generally accepted temperature differential limit, or other criteria? How do the pipe stress masters determine which lines to analyze and which should be ok?!?

#108 - 06/09/00 01:46 AM Re: Rigorous Analysis Guidelines
Ohliger Offline

Registered: 12/16/99
Posts: 246
Loc: Mannheim,Germany
I have rules for piping with diameter less than 50 mm.This rules we take for nuclear power piping.
The adjourment of the pipe hat to fill conditions like restraint distance.
The distance of the restraints and the necessary free pipe leg is dependent from
temperature,diameter and thickness!

#109 - 06/09/00 11:01 AM Re: Rigorous Analysis Guidelines
Jim Wilcox Offline

Registered: 12/20/99
Posts: 46
Loc: Calgary, AB, Canada
The following guidelines are a combination of a list I obtained from Coade years ago, and a list from a consulting engineering company here in Canada. Hope it helps.
In case it is of interest, we're conducting a CAESAR II pipe stress seminar in Calgary, AB, June 19 - 23.

When to Perform Pipe Stress Analysis:
1. Lines that are 3 inch and larger that are:
a) connected to rotating equipment,
b) subject to differential settlement of connected equipment and/or supports,
c) with temperatures less than 20 F.
2. Lines connected to reciprocating equipment such as suction and discharge lines from reciprocating compressors.
3. Lines 4 inches and larger connected to air coolers, steam generators or fired heater tube sections.
4. All size lines with temperatures of 600 F and higher.
5. Welded lines 6 inches and larger at a design temperature of 350 F or higher.
6. Lines 16 inches and larger (any temperature differential), because of large F=P*A thrust forces
7. High pressure lines (over 2000 psi), although pressures over 1500 psi are sometimes a problem, particularly with restraint arrangements.
8. Lines subject to external pressure.
9. Thin-walled pipe or ducting of 18 inch diameter or larger, having an outside diameter over wall thickness ratio of more than 90.
10. Lines requiring proprietary expansion devices, such as expansion joints or victaulic couplings.
11. Underground process lines. Pressures greater than 1000 psi in underground piping inevitably generates high thrust forces, even at very low expansion temperature differentials. Attention is required on burial techniques, changes in direction, ground entry/exit, or connection to equipment or tanks. Other examples include pump/booster stations, terminals, meter stations and s****er traps.
12. Internally lined process piping & jacketed piping.
13. Lines in critical service.
14. Pressure relief systems. Also relief valve stacks with an inlet pressure greater than 150 psi.
15. Branch lines tie-ins or matched size, particularly relief systems tied together or large branch piping of same size or close to piping being connected.

#110 - 06/11/00 07:38 PM Re: Rigorous Analysis Guidelines

Your question is more complex than you realize perhaps. It is commonly asked, and always reminds me of one of my bosses who in an effort to speed up the work said "only check the portions of the drawing which are wrong!" Anyhow, as you can imagine after I heard that statement I realized that some people do not understand the complexity of a given task.

The analysis of lines or should we say systems and sub-systems, is really a sorting out process as you have implied by the word culling. That is in order to evaluate a systems flexibility you need the system geometry and restraint conditions. There is no way to eliminate these needs entirely. You can ignore ambient lines if you like but, I have had to increase flexibility in even these types lines to account for differential structure movements.

If you are on a limited budget concentrate on the obvious… hot process and steam lines, and lines above 200F attached to rotating equipment. However, I strongly suggest that you eyeball more than less… while recently eyeballing another consultants work I found two anchors 60 feet apart (on the same header) on a stainless steel line that operated around 200F or so, I don't need a computer to tell me that this is a bad idea! Good Luck!

Best Regards,

John C. Luf


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