Tube Skin Thermocouple Assembly
The REFRACTO-PAD™ accurately measures tube skin temperature in fired process furnaces and boilers. The patented REFRACTO-PAD™ thermocouple is designed to minimize temperature measurement problems caused by flame impingement and radiant heat. The accurate monitoring of tube skin temperature increases furnace efficiency, provides accurate tube life data, and assists in decoking operations
Design and Installation
Proper installation of the Refracto-Pad™ is the single most critical factor in assuring long thermocouple life. Successful Refracto-Pad™ installations are achieved through prior planning and adherence to these guidelines, and result in optimum sheath protection. An important fact to remember is that there is no one answer applicable to all furnaces. Each installation must be given individual consideration to ensure optimum thermocouple performance. Two primary factors contribute to the successful Refracto-Pad™ installation. First, keep the thermocouple sheath in intimate contact with the process tube and on its coolest side if possible. In many furnaces there is no cool side of the tube. When this is the case it is even more important to keep the sheath in contact with the tube. Second, allow for expansion and movement associated with furnace tubes. Keeping these two consideration in the forefront of your planning will result in a successful installation and a long Refracto-Pad™ life.
Contact and Routing
Keeping the thermocouple sheath in intimate contact with the tube and routing it on it's coolest side are of paramount importance because it allows the thermocouple to utilize the process tube as a heat sink. The thermocouple sheath remains close to the same temperature as the tube, thereby ensuring it's normal life expectancy. This is best accomplished by the liberal use of weld on "tube-clips". A sufficient number of tube clips most be used to ensure that all portions of the thermocouple sheath exposed to radiant heat and/or direct flame impingement remain in contact with the tube. Only where tube clips are impossible to use, or where time constraints are a consideration, should banding be considered. Please note that keeping the thermocouple sheath in contact with the tube occasionally requires drilling through the tube support structure.
Expansion and Growth
Furnace tubes reaching process temperature will move a substantial distance (two to twelve inches is typical). Such movement will destroy the thermocouple if no compensation is provided. Tube growth compensation can be achieved with expansion coils or on the outside of the furnace fire box. However, compensation outside the furnace is, in many cases, the best approach. The optimum location for the expansion loops is just before the furnace firebox exit. It is recommended that this be done at floor level to minimize exposure to flame and/or radiant heat.
Theses are only guidelines. Due to limitations of time, material and labor, compromises are often necessary. Such compromises however, may shorten the life of the Refracto-Pad™ thermocouple assembly. Nonetheless, the Refracto-Pad™ is relatively inexpensive in material and installation costs. This is especially true when comparing it toother tube skin designs.