ASHRAE Journal - July 2020 - 47

COLUMN ENGINEER'S NOTEBOOK

and popped the covers off (Photo 2).
4. Sufﬁcient guidance of the
pipe by alignment guides and rigid
anchoring at both ends prevents
snaking or bowing, i.e., the pipe
compresses. This can be an effective strategy for materials with low
strength (mostly plastics), but with
steel pipes the forces are usually
much too high, and the anchors
break. One of the authors vividly
remembers a steam tunnel in which
12, ¾ in. (19 mm) bolts were sheared
off, and the anchor had moved 6 in.
(152 mm) down the tunnel.
We do not recommend designs
that rely only on scenarios three and
four.
A good example of Scenario 1
is a steam pipe that goes from a
basement to a penthouse (Figure 2)
and is left free to "ﬂoat" at the bottom of the shaft. In this case we
normally hang the pipes from the
top and use spring hangers (the
same type used for vibration control) near the riser at the bottom.
Capacities of threaded rods are in
the 2016 ASHRAE Handbook-HVAC
Systems and Equipment, Chapter 46,
Table 9; however, the capacity of the
anchor or upper support is often the
limiting factor.
This method avoids the need for
alignment guides (Photo 3) or any
intermediate supports. It does
require a strong hanger at the
top, so you may want to calculate
the maximum load on the upper
hanger and note that on the plans.
For plastic pipes ﬁlled with water,
always check with the supplier
about whether the joints are rated
not to separate under this much
weight.
This strategy can also work in
reverse. We designed a chilled water

FIGURE 1 Pipes exiting a shaft.

PHOTO 1 Riser expansion affecting ﬁre rating. Note
that pipe is off-center and appears deﬂected.

Pipe Expansion

TABLE 1 Coefficients of thermal expansion, allowable stress and stiffness.
MATERIAL

EXPANSION 1

S A2

Steel A53B ERW or
Seamless

0.76

22,500

27.50

Stainless Steel

1.12

19,300

28.55

Copper

1.14

13,500

PVC/CPVC

4.20

1 to 2,0005

0.42

Polypropylene

7.20

Note 5

0.13

FRP4

1.08 to 1.57

2,500

RTRP aka GRP or

1. Per the 2016 ASHRAE Handbook-HVAC Systems and Equipment, p. 46.9, Table 7, expansion values are in in. per 100 ft
(30 m) per 100°F (56°C). The Handbook shows these values in in. per (106 in. × °F). In this table they are converted to in. per
100 ft (30 m) per 100°F (56°C).
2. SA = Allowable stress (psi). Values are from 2016 ASHRAE Handbook-HVAC Systems and Equipment, p. 46.1. Furnace
welded A53 steel is rated at 16,900 psi (117 MPa), and the Handbook suggests using 15,000 psi (103 MPa) for steel pipe.
3. E = modulus of elasticity (× 106 psi) or Young's modulus (106 psi), aka stiffness. Values are from 2016 ASHRAE
Handbook - HVAC Systems and Equipment, 46.9, Table 7.
4. RTRP is the most generic and stands for reinforced thermosetting resin pipe. Glass reinforced plastic (GRP) and ﬁber
reinforced plastic (FRP) are limited to pipes with glass ﬁber ﬁlaments, which are by far the most common. But, RTRP also
includes other ﬁlaments such as carbon ﬁber or carbon and other ﬁber types. The values in this table are based on glass
ﬁber reinforcement. As a rule, vinyl ester binding is best for corrosion resistance (e.g., fume exhaust ducts), and epoxy resins
may be best for applications that require high strength.
5. SA varies greatly with temperature.

plant with large steel condenser
pipes going up ~12 stories to existing
cooling towers. We anchored it with
a welded angle ring at the base and
installed alignment guides up the
side of the building.
If the pipe is constrained as in
Scenario 2 above, we now look at

ways to accommodate this. There are
several options.
The ﬁrst option is offsets to reduce
stresses in the pipe to acceptable
levels. These are often L-bends
(Figure 3 ), Z-bends (Figure 4) or
U-bends. Their design is described
in the 2016 ASHRAE Handbook-HVAC

J U LY 2 0 2 0

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ASHRAE Journal - July 2020

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