PIPING AND ASSOCIATED EQUIPMENT
THERMAL INSULATION AND FREEZE PROTECTION
1 INSULATION. A thermal insulating material resists the flow of heat through
it and is used in heat distribution systems for the following purposes:
q To prevent heat loss
q To prevent condensation of steam in steam lines
q T o m a i n t a i n d e s i r e d f l u i d temperatures
q To protect personnel from h i g h temperatures, as in manholes and pits
1 . 1 Economic Studies. With fuel a n d material costs soaring over the past
s e v e r a l years. previous standards o f insulation thickness have been discarded
i n favor-of much higher values. As an example, in 1962 a 24-inch steam line
a t 1,050F required 5.5 inches of insulation. On the basis of 1973 costs, the
r e q u i r e m e n t was 6.0 inches of insulation; h o w e v e r , when costs at the midlife
o f the insulation were taken as a basis, the thickness requirement had
i n c r e a s e d to 9.5 inches. Most commercial plants have adopted the midlife cost
m e t h o d on the assumption that fuel and other costs will continue to increase.
The number of factors involved in energy management complicates the selection
o f optimum insulation thickness and usually requires a comprehensive study of
i n s u l a t i o n thickness economics. The Thermal Insulation Manufacturers
A s s o c i a t i o n provides guidance for such studies.
1 . 2 S e l e c t i o n o f I n s u l a t i o n M a t e r i a l . In discussing insulating materials,
t h e "k' factor or thermal conductivity of the material must be understood.
T h e k factor is the amount of heat, in Btu/hour that flows through a slab of
i n s u l a t i o n l - f o o t s q u a r e , a n d l-inch thick when one face is 1F hotter than
t h e other. K factors for insulation typically vary from about 0.25 to over
1 . 0 0 depending upon the material and the temperature. The heat flow in Btu's
p e r hour per square foot is equal to k times the temperature difference ("F)
d i v i d e d by the thickness (inches). In commercial applications, a low k factor
i s of fundamental importance in selecting an insulation material. However, in
m o s t applications, t h e final material selection may entail some compromise of
t h e k factor in favor of other properties. Insulation strength is of obvious
i m p o r t a n c e if the insulation must withstand dropping, stacking, impacts, or
v i b r a t i o n . However, when strengthening agents are added, this normally
r e s u l t s in additional heat conduction paths and the k factor is increased.
T h e same would be true should insulation stiffness be a required property.
T h e binders or spacers that must be added to the insulation result in a higher
k f a c t o r . The same considerations generally hold true when resistance to
m o i s t u r e , dimensional stability, or fire resistance are required properties.
1 . 3 I n s u l a t i o n P r o p e r t i e s . Table 7-1 lists common types of insulations with
t h e i r maximum temperatures, k factors, and density. Other properties are
l i s t e d below.
( a ) C a l c i u m S i l i c a t e . This is a molded insulation with a usable
temperature range of 100F to 1,200F. Flexural strength is approximately