Subject: Install Expansion / Contraction Joints to Eliminate Gapping Between Insulation Sections

Thermal expansion/contraction is a concern both for insulation systems that operate continuously at below ambient conditions or systems that cycle between below-ambient conditions and elevated temperatures.

The coefficient of expansion or contraction is the material property which measures its dimensional change relative to a change in its temperature. When heated or cooled, materials, such as steel, will expand or contract at a constant rate. These changes are reversible, since the materials will return to their original dimension when their temperature returns to where it was before being heated or cooled. This reversibility distinguishes the coefficient of expansion/contraction from two other properties relating to dimensional changes; dimensional stability and linear shrinkage: neither of which is reversible.

Not all insulation materials exhibit the ability to return to their original size. It is limited to cellular glass and rigid organic foams such as: phenolic, extruded polystyrene and polyisocyanurate.

A large difference in the amount of contraction between the insulation and the piping may result in open joints of the insulation system when the pipe is cooled down to operating temperature. These open joints not only create a thermal short circuit at that point in the system, but may also affect the integrity of the entire system. Sweating, icing or mildew may occur depending on the amount of moisture present and the ambient temperature versus operating temperature. Insulation materials that have large contraction coefficients, and do not have a high enough tensile strength or compressive strength to compensate, may experience shrinkage and subsequent cracking within the material.

At the elevated temperature end of the cyclic process, the reverse is considered. High thermal expansion coefficients may result in warping or buckling of a material that for some insulation materials is permanent and irreversible. In this instance, the possibility of resulting stress on an external vapor retarder or weather barrier should be considered.

The installation of expansion/contraction joints will build compatitibility into your system between the pipe and the pipeline insulation. The spacing of these joints will depend on the line operating temperature, free span or length of pipe and the individual material coefficient of expansion or contraction at the operating temperature.

Joints on horizontal lines shall be located at midpoint between two pipe supports and other protrusions through the insulation system. On vertical lines and equipment, the joint shall be located directly below the insulation support ring which is a clamped-on support. This clamp-on support shall be located directly above any elbows and then at every 24 foot interval.

Construction of the expansion/contraction joint shall include three inch (75mm) thick uncompacted fiberglass which shall be compacted to 1" thick between pipe insulation sections. Single layer and multi layer applications shall have an additional layer of equivalent thickness insulation of the pipeline insulation installed as an outer cover over the expansion/contraction joint. The length of the additional layer shall be 12 inches minimum. Vapor and/or weather barriers must be maintained continuous over the joint by stepping up and then down back to the pipe insulation

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