ASHRAE Journal - July 2020 - 49

COLUMN ENGINEER'S NOTEBOOK

Flexible mechanical couplings (Photo 7) offer another
option. The advantages of this approach are that little or
no extra shaft space is required (depending on insulation thickness), often there is no added cost, and little or
no increased risk of a failure. The concerns about pipe
breakage or becoming too eccentric to conform with
ﬁrestopping UL listings are easily dealt with by locating
anchors near each branch that leaves the shaft and having the expansion occur between branches. A few years
ago, mechanical coupling systems also became available
for low pressure steam.

FIGURE 3 (TOP) L-bend. FIGURE 4 (BOTTOM) Z-bend. (Source: 2016 ASHRAE
HandbookÑHVAC Systems and Equipment, Chapter 46.)

Δ

A
B
Anchor
L

C
t

L
Guide

Example 1
6 in. (152 mm) Diameter Schedule 40 Steel Steam
(12 psig ≈ 245°F [83 kPa ≈ 118°C]) Pipe Going from
Basement to Penthouse, 10 Stories, 14 ft/story (4.3 m/
story)
0.76 in.
= 1.86 in.
100°F × 100 ft

(2)

The total expansion for 140 ft (43 m) of steel pipe in the
shaft is 1.86 in. (47.2 mm). If we choose to rigidly support the pipe at the penthouse (i.e., hang the pipe) and
allow the pipe to expand into the basement, we effectively turn the expansion into a simple L-bend calculation (refer to 2016 ASHRAE Handbook-HVAC Systems and
Equipment, Chapter 46, p. 46.11). If the pipe expands into
the basement, the ﬁrst few hangers need to be able to
permit this expansion. Otherwise, the expansion forces
are great enough that it could break the hanger.
Using Equation 5 of the 2016 ASHRAE Handbook-HVAC
Systems and Equipment, Chapter 46, p. 46.11, we can calculate the location of the ﬁrst rigid hanger. Using this
equation, the ﬁrst rigid hanger should be at least 17 ft,
8 in. (5.4 m) in from the shaft piping. If 6 in. (150 mm)
diameter piping is spaced at 12 ft (3.7 m) o.c., the ﬁrst
PHOTO 4 Packed slip expansion joint.

Guide
L
Anchor-to-Anchor Expansion
Distance from guides, if used, to offset should be equal to or exceed the length of offset.
Offset piping must be supported with hangers, side plates and spring hangers similar to
those for L-bends.

two hangers should be spring hangers with 2 in. (51 mm)
deﬂection to allow the pipe to expand. The third hanger
can be rigid. The force due to the deﬂection on the third
hanger at 17 ft, 8 in. (5.4 m) is approximately 2,655 lbf (11
810 N) using Equation 7 of the 2016 ASHRAE Handbook-
HVAC Systems and Equipment, Chapter 46, p. 46.11. The
forces at the third hanger will reduce as the hanger is
moved away from the shaft.
Another option is to use intermediate ﬂexible couplings with a rigid hanger at the bottom. This avoids the
need for spring hangers.

Example 2
180°F (82.2°C) Maximum Steel Heating Water Pipe
From Basement to Penthouse, Taps on Each Floor, 10
Stories at 14 ft/story (4.3 m/story)
PHOTO 6 Flexible U-bend.

PHOTO 5 Bellows joint with braided stainless steel outer

IMAGE BY BRIJESH PANCHAL (IMEG) AND METRAFLEX

IMAGE BY BRIJESH PANCHAL (IMEG)

wrap.

IMAGE BY BRIJESH PANCHAL (IMEG)

(245°F − 70°F) × 140 ft ×

L

J U LY 2 0 2 0

ashrae.org

ASHRAE JOURNAL

49
http://ashrae.org
ASHRAE Journal - July 2020

Table of Contents for the Digital Edition of ASHRAE Journal - July 2020
