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COPPER EXPANSION AND
CONTRACTION
Copper Expansion and Contraction
Under normal operating conditions, the vapor pipe temperature of a
in pipe temperature, the designer must consider pipe expansion and
contraction to avoid pipe and fitting fatigue failures.
Refrigerant pipe along with the insulation jacket form a cohesive
unit that expands and contracts together. During system operation,
thermal heat transfer occurs between the pipe and the surrounding
insulation.
If the pipe is mounted in free air space, no natural restriction to
movement is present if mounting clamps are properly spaced and
installed. When the refrigerant pipe is mounted underground in a
utility duct stacked among other pipes, natural restriction to linear
movement is present. In extreme cases, the restrictive force of
surface friction between insulating jackets could become so great
that natural expansion ceases and the pipe is "fixed" in place. In this
situation, opposing force caused by change in refrigerant fluid/vapor
temperature can lead to pipe/fitting stress failure.
The refrigerant pipe support system must be engineered to allow
free expansion to occur. When a segment of pipe is mounted
between two fixed points, provisions must be provided to allow pipe
expansion to naturally occur. The most common method is the
inclusion of expansion Loop or U-bends mounted in the horizontal
plane. When expansion loops are placed in a vertical riser, the loop
is to be formed in a horizontal fashion resulting in a torsional move-
ment during expansion and contraction. Each segment of pipe has
a natural fixed point where no movement occurs. This fixed point is
located at the center point of the segment assuming the entire pipe
is insulated in a similar fashion. The natural fixed point of the pipe
segment is typically where the expansion Loop or U-bend must be.
Linear pipe expansion can be calculated using the following formula:
LE = C x L x (T
– T
) x 12
r
a
LE
=
Anticipated linear tubing expansion (in.)
L
=
Length of pipe (ft.)
T
r
T
a
12
=
Inches to feet conversion (12 in./ft.)
38
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1. From the table "Linear Thermal Expansion of Copper Tubing in
Inches," find the row corresponding with the actual length of the
straight pipe segment.
2. Estimate the minimum and maximum temperature of the pipe.
Typical pipe temperature change ranges: High Pressure Vapor:
extreme. In the column showing the minimum pipe temperature,
look up the anticipated expansion distance. Do the same for the
maximum pipe temperature.
3. Calculate the difference in the two expansion distance values.
The result will be the anticipated change in pipe length.
General Example:
A system is installed and the design shows that there is a 100 foot
straight segment of tubing between a Y-branch and a branch distribu-
tion unit. The system operates 24 hours per day. In heating, this pipe
same tube is a suction line returning refrigerant vapor to the outdoor
ture and calculate the difference.
Vapor Line
Anticipated Change in Length: 1.40 in. – 0.40 in. = 1.00 in.
Liquid Line
The liquid temperature remains relatively the same temperature; only
the direction of flow will reverse. Therefore, no significant change in
length of the liquid line is anticipated.
When creating an expansion joint, the joint depth must be a
minimum of two times the joint width. Although different types of
expansion arrangements are available, the data for correctly sizing
an expansion loop is provided in the table "Coiled Expansion Loops
and Offsets (Plan View)." Use soft copper with long radius bends
on longer runs or long radius elbows for shorter pipe segments.
Using the anticipated linear expansion (LE) distance calculated, look
up the Expansion Loop or U-bend minimum design dimensions. If
other types of expansion joints are chosen, design per ASTM B-88
Standards.
F
MULTI
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MULTI
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