Im not qualified to answer but my opinion is that much of these standards were
put In place for industry before internet, etc.
So that every job does not need to be reviewed by an engineer.
I was told the 250 lb requirement was to support the weight of the fitter
hanging the pipe. I don't know why the 5X rule was added.
The standard always has allowed for equivalency in product or requirement.
Sent from my Galaxy S®III
-------- Original message --------
From: "Hinson, Ryan" <rhin...@burnsmcd.com>
Date: 10/29/2013 2:38 PM (GMT-05:00)
To: sprinklerfo...@firesprinkler.org,k...@parsleyconsulting.com
Cc: "Leahy, Andrew P" <aple...@burnsmcd.com>,"Reene, Kevin"
<kre...@burnsmcd.com>,"Eberly, M. David" <mebe...@burnsmcd.com>,"Jordan,
David" <djor...@burnsmcd.com>
Subject: Pipe supports revisited (Pipe support spacing requirements for
structural supports)
I'm getting tired of going toe-to-toe with every structural and piping engineer
regarding fire protection related pipe support and spacing requirements on
every time I work on a refinery-type project and hoping a hanging and support
committee member might weigh in here. The spacing limitations and required
loading per pipe support in conformance with NFPA is actually driving a
potential $200K cost increase just for the pipe supports (of which FW piping is
but one of several supported systems) on a single project.
Two questions:
1. Does anyone know why the safety factor is 5X the weight of the
water-filled pipe exists or from where it originates? The 2013 edition of NFPA
13 has been revised from the 2010 edition and commentary has been included
requiring structural engineers to also design for 5X.... Section 9.1.1.2
requires SE's to design supports to include:
- 5X the weight of the water-filled pipe plus 250 lbs
2. Why is spacing limited to 15 ft...with one known exception? NFPA 13
(2013) Section 9.1.1.2 further limits SE's to:
- Spacing of supports cannot exceed 15 ft per Tables 9.2.2.1(a & b)
...which only includes piping through 8".
Some supporting Code:
- NFPA 13 Section 9.1.1.3.1.1 allows pipe support design to use 5X...
based on ultimate stress while Section 9.1.1.3.1.2 allows it to be done using
5X... and 1.5X the weight of the other supported systems. Both these sections
require reference back to Section 9.1.1.2 only allowing spacing to 15 ft.
- It appears that NFPA forcing pipe support design through a pretty
small window through which can be designed though not its primary function.
- It should also be noted that NFPA 15 (2012) Section 6.3.2.2.2 allows
a limited extension of support spacing with the addition of diagonal
bracing...again, only pipe sizing up through 8" is addressed.
- NFPA 24 (2013) and NFPA 13(2013), both Sections A.10.4.1(3), refers
to AWWA M11 for applicable documents for the installation of pipe and fittings
which allows distances exceeding those in NFPA 13 Tables 9.2.2.1(a & b) or NFPA
15 Table 6.3.2.2.2 (though this is specifically for depth of cover subject
matter).
o AWWA M11 Chapter 7 states the load is determined to be the weight of the
water filled pipe.
o AWWA M11 Chapter 7 gives several spanning maximums which far exceeds those
allowable in NFPA.
§ Take 8" Schedule 40 pipe as an example:
· The wall thickness is .322 inches.
· Per Table 7.1, this approximately nominal 5/16" wall thickness can
have supports 45 ft apart...compare to 15 ft.
Follow-up questions:
1. How can this; or can it be - reconciled in the refinery industry where
most all piping is standard weight as a minimum, welded or weld-flanged, and
all piping supports are calculated to at least 20 ft spacing? While
hydrocarbon product piping is not life safety related, surely, sufficient
safety considerations have been factored into the 1.5X... safety factor for
this type of pipe.
2. Why does firewater (life safety) piping require safety factors and
limit support spacing to much more conservative values than that of piping
systems actually containing flammable and hazardous products with little or no
allowance for 'structural engineering' to take place?
Thank you,
Ryan L. Hinson, PE*, SET
Senior Fire Protection Engineer, Aviation & Federal Group,
P&I GP Liaison
Burns & McDonnell
Minneapolis-St. Paul Office
8201 Norman Center Drive, Suite 300
Bloomington, MN 55437
Direct: 952-656-3662
Mobile: 320-250-5404
Fax: 952-229-2923
www.burnsmcd.com<BLOCKED::www.burnsmcd.com>
*Registered in MN
Proud to be #18 of FORTUNE'S 100 Best Companies to Work For
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