Bruce,
Your comments based on your experience with these sanitary piping systems matches what I have heard reported by those that operate these systems. Even so, the piping must meet the requirements of B31.3. So, I don't see the usefulness of describing something "almost exempt" from the code.
Agreed, that smaller piping is more flexible than large. Even so, smaller piping does often require analysis, and temperature difference is coupled to the decision as to when to formally analyze the piping. In the subject case we are dealing with 6 inch tubing. In Charles Becht IV's "Process Piping Guide to B31.3", his recommendation for formal analysis is for NPS 4" and larger with 400 deg. F differential, and NPS 8" and larger with 300 deg. F differential. With the subject case, given that stainless steel tubing is employed, the tubing size, a differential of about 100 deg., the complexity of the piping run, and the presence of hygienic unions, a formal pipe stress analysis seemed wise.
Ken A. Nisly-Nagele, P.E.
Project Engineer, Mechanical
Applied Engineering Services, Inc.
7999 Knue Road
Indianapolis, IN 46250
317-585-8920
-----Original Message-----
From: Bruce Bullough [mailto:bbullough@sebesta.com]
Sent: Monday, May 24, 2004 9:45 AM
To: PipingDesign@yahoogroups.com
Subject: RE: [PipingDesign] Modeling Hygienic Unions [text][bcc][faked-from]
Having worked for several years in industries where product changeovers and contamination control are paramount, I have done a lot of checking into use of sanitary fittings in hazardous/flammable service, and have been unable to find ANYONE who will, even off the record, consider that they meet the requirements of B31.3, because they do leak and are subject to misalignment and damage to the seal. The closest I've been able to come is with compression fittings (some will agree that, although excluded by B31.3, probably ought to be allowed and probably meet the intent of the code), but they are limited to very small systems (nominally 25mm and under) or a square-threaded type of union (difficult to find in N America, but readily available in all common sizes under 150mm in Europe). \
Have to ask if the inherent flexibility of small pipe doesn't almost exempt it from B31.3 in many cases.
... Bruce D. Bullough ...
Sebesta Blomberg & Associates, Inc.
2381 Rosegate
Roseville, MN 55113 USA
+ 651-459-6659
www.sebesta.com
>The code I am most concerned with is B31.3 which states the pipe flexibility
requirements, the BPE code is mostly addressing dimensions and issues
>>>relating to sanitization. B31.3, para. 319.1.1 requires a leak free system.
As Aaron comments, the unions usually work initially, but often leak. If the
system is designed to cycle thermally, and will leak after "x" number of cycles,
does that meet B31.3? It seems to me since the intent of B31.3's flexibility
requirements is to end up with a system that can cycle thermally and still not
leak, these joints can not be shown to comply.
Ken A. Nisly-Nagele, P.E.
Project Engineer, Mechanical
Applied Engineering Services, Inc.
7999 Knue Road
Indianapolis, IN 46250
317-585-8920
-----Original Message-----
From: Aaron Wolfe [mailto:aaronwolfeman@hotmail.com]
Sent: Friday, May 21, 2004 8:46 AM
To: PipingDesign@yahoogroups.com
Subject: RE: [PipingDesign] Modeling Hygienic Unions
Ken,
In my experience the clamps hold up well to thermal expansion....If the line is designed with sufficient change of direction to handle the force. The MHP style could be used in high pressure situations. But over time they just leak. I work in mostly bio-pharm systems. And the places where clamps are required are for removable spools for sterilization, calibration of an instrument, or connection to a piece of equipment. It is standard practice to minimize the use of such clamps because like I said, eventually they just leak. This is due to the gasket being repeatedly fatigued by clamping and unclamping. A quick replacement and they are good for another round. Being Autoplant users, we use AutoPIPE for the "stress test" and it seems to handle the clamp fitting just fine.
Regards,
Aaron Wolfe
Piping Designer
Paul Mueller Company
P.O. Box 828
Springfield, Mo 65801
(417) 575-9780
E-mail: awolfe@muel.com
-----Original Message-----
From: Ken Nisly-Nagele [mailto:knislynagele@applied-e-s.com]
Sent: Thursday, May 20, 2004 5:43 PM
To: PipingDesign@yahoogroups.com
Subject: RE: [PipingDesign] Modeling Hygienic Unions
These clamps are made by Tri-Clover, Waukesha, or Swagelok, and are rated to 200 psig. By meeting code, I mean to demonstrate that the unions will not leak during sterilization. I'm not concerned about the clamps working at the design pressure, but rather, I'm concerned with the clamps leaking when the piping in which they are installed undergoes bending during thermal expansion and causes the faces of the ferrules to spread apart and result in leakage. With standard flanges there are tools to predict leakage, but I am not aware of a way to check for leakage with a union of this type. It may be that the only solution is to ask the manufacturers to test and publish the data as a group or individually.
Ken A. Nisly-Nagele, P.E.
Project Engineer, Mechanical
Applied Engineering Services, Inc.
7999 Knue Road
Indianapolis, IN 46250
317-585-8920
-----Original Message-----
From: Christopher Wright [mailto:chrisw@skypoint.com]
Sent: Thursday, May 20, 2004 5:00 PM
To: â¡
Subject: RE: [PipingDesign] Modeling Hygienic Unions
>My apologies, my initial posting was not sufficiently clear.
No problem. Are you talking about clamps like the Grayloc or Tri-Clover variety?
>The question is one of
>applying the unions and demonstrating compliance with the code.
I think the easy for doing this is to show that your clamp meets the code rules
for a pressure which produces a unit axial load equal to the (calculated axial
pressure stress + the calculated bending stress)/pipe wall thickness. This is
fairly conservative, but it'll meet the U-2(g) requirements without a lot a
extra work.
Christopher Wright P.E. |"They couldn't hit an elephant at chrisw@skypoint.com | this distance" (last words of Gen. ___________________________| John Sedgwick, Spotsylvania 1864)http://www.skypoint.com/~chrisw
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