Bolt-on jacketing features a 2-in by 1-in rectangular heating element which is secured to the pipe or vessel to be heated. A heating medium such as steam or hot oil flows inside the heating element and transfers heat to the pipe/vessel. One of the 2-in sides of the element is contoured to closely fit the outside diameter of the pipe/vessel to ensure good contact for heat transfer. A thin layer of heat transfer compound is used between the element and the pipe/vessel to eliminate any air gaps between the jacketing and the pipe/vessel wall.
Bolt-on jacketing is not capable of the maximum heat transfer rates attainable with jacketed piping. However, the amount of heat transfer can be tuned to the process needs by adjusting the number of elements used. Furthermore, using heat transfer computer modeling, the wall temperature distribution can be evaluated for determining the required element spacing for maintaining a minimum wall temperature. Bolt-on systems can offer enough heat for many heat exchange problems, but because jacketed piping offers higher heat transfer rates, some heat exchanger problems may be better suited for jacketed piping if cross contamination is not a concern. Each case should be analyzed individually.
Safety and Reliability
There is no cross contamination potential with bolt-on jacketing. System reliability is contingent upon the installation quality. Reliability is strengthened by the fact that bolt-on systems are generally engineered systems and pre-fabricated per the piping isometrics. Multiple heating elements around the pipe/vessel circumference can be connected into a single panel with one steam inlet and one condensate outlet. This reduces the total number of circuits over other single-element heating systems, which improves system robustness.
Bolt-on jacketing systems are generally less expensive than jacketed piping, and the cost savings increase significantly with increasing pipe size. When comparing the cost of bolt-on jacketing to tube tracing, the total system cost must be considered. This includes the capital costs of the jacketing, the capital costs of the required utilities infrastructure, and the ongoing operational costs of the jacketing/utilities. Utilities infrastructure is a much bigger component of a tube tracing system compared to a bolt-on jacketing system (60% of total system cost versus 20%), so an economic analysis may be required to fully evaluate the two technologies for a given project.