TUBULAR ELEMENT INSTRUMENTED WITH TEMPERATURE SENSORS, IN PARTICULAR FOR MEASURING OVERTEMPERATURES IN THE TUBES OF THERMOELECTRIC POWER PLANT SUPERHEATERS

Abstract: This invention relates to a tubular element provided with a temperature sensor, in particular for measuring overtem­ peratures in the tube bundle of superheaters in thermoelec­ tric power plant steam generators, comprising a pair of concentric tubes (11,12) forcibly locked one into the other by a mechanical plastic deformation process, at least one of the two tubes comprising in the mutually contacting surfaces a series of longitudinal grooves (13) into which said tempera­ ture sensors (15) are inserted.

Description: This invention relates to a tubular element in which temperature sensors are inserted into suitable essentially longitudinal seats provided in the wall of said tubular element. when suitably disposed, said tubular element specifically enables the temperatures of superheater tube walls to be measured, in order to enable any exceeding of the allowable temperature limits to be immediately checked. Measuring the wall temperatures of the constituent tubes of a superheater is known to be of particular importance, as said tubes are subjected to large temperature gradients, to aggressive products of combustion, and to high temperatures. This measurement is currently made using commercial thermocouples mounted on the tube surfaces and/or suitably supported on the outside of the tubes. The aforesaid chemical and physical conditions enable thermocouples mounted in this manner to operate correctly only for periods of a few weeks, such periods being unacceptable and of little significance in the effective control of the plant. There are currently no superheaters which are instrumented or provided with protective systems and alarms which make it possible to act in order to save the tube bundle, in pnttIeular during the temperature transients at plant start-up. The object of the present invention ii to provlde r device able to make local zesurements of the tube wall temperatures to enable any exceeding of the temperature limits tolerable by the stperheater to be immediatel r checked. This object Is attained by a tubular element provided with a temperature sensor, in particular for measuring overtemperatures in the tube bundle of superheaters in thermoelectric power plant steam generators, characterised by comprising a pair of concentric tubes forcibly locked one into the other by a mechanical plastic deformation process, at least one of the two tubes comprising in the mutually contacting surfaces a series of longitudinal grooves into which said temperature sensors are inserted. The characteristics and advantages of an instrumented tubular element constructed in accordance with the present invention will be snore apparent from the description given hereinafter with reference to the accompanying diagrammatic drawings in which: Figure 1 is a partly broken longitudinal section through an instrumented element according to the invention; Figure 2 is a cross-section through an element such as that of Figure 1; and Figure 3 is a cross-section equivalent to that of Figure 2, before undergoing a drawing process. With reference to the drawings, a tubular element according to the invention indicated by 10 comprises a first tube 11 into which a second tube 12 is concentrically inserted with a gap of a few tenths of a millimetre. A series of longitudinal grooves 13 are ponced in the e't±r surface of the second tube 12, and have a cro@@-section of essentially circular profile, obtained for example by Thtlling followed by smoothing or polishing. The two tubes 11 and 12, inserted one into the other, are subjected to mechanical cold-drawinr, effected wtth an internal mandrel, which forces the two said tubes together to create positioning seats 14 for thermocouples 15. In the vicinity of an end portion 17 of said tubular element 10 constituted in this manner there are provided arcuate bores or seats 16 which connect the seats 14 to the outside of the tubular element to enable the thermocouples 15 to be connected to measuring systems (not shown). An end portion 17 of the tubular element 10 which is free from thermocouples 15 enables it to be assembled by welding, with the thermocouples 15 already inserted, these latter undergoing no danger of damage and emerging into a zone which is not exposed to the aggressive fluids, and lies beyond a wall 18. The drawing process carried out with an internal mandrel provides for a tube diameter reduction of 5-lOX and a simultaneous analogous thickness reduction so that the two tubes remain strongly forced together to provide good thermal contact. Before being drawn, the contacting surfaces undergo chemical pickling treatment and the surfaces which slide in the drawbench undergo bonderizing. The state of tension induced by the drawing operation, together with the pressure of the process fluid inside the tubular element, oppose any separation of the two tubes caused by differential expansion in the presence of temperature gradients. In particular, for equal total thicknesses (ie the sum of the two), it is convenient to thin-down the tube exposed to the fluid of higher pressure. Furthermore, in order to improve thermal contact between the two tubes inserted one into the other, a series of longitudinal welds can be provided in suitable number, made for example by means of an electron beam or a similar method.

Claims: CLAIMS: 1. A tubular element provided with a temperature sensor, in particular for measuring overtemperatures in the tube bundle of superheaters in thermoelectric power plant steam generators, characterised by comprising a pair of concentric tubes forcibly locked one into the other by a mechanical plastic deformation process, at least one of the two tubes comprising in the mutually contacting surfaces a series of longitudinal grooves into which said temperature sensors are inserted. 2. A tubular element as claimed in claim 1, characterised in that said locking is effected by drawing. 3. A tubular element as claimed in claim 1, characterised in that said grooves are provided in the outer surface of the inner tube. 4. A tubular element as claimed in claim 1, characterised in that said grooves are provided in the inner surface of the outer tube. 5. A tubular element as claimed in claim 1, characterised in that said grooves are connected, in proximity to at least one end of said tubular element, to the outside of said tubular element by means of smoothly joined arcuate bores. 6. A tubular element as claimed in claim 1, characterised in that a series of longitudinal welds are provided by the electron beam or similar technique on the surface of said concentric tubes in order to improve thermal contact between said tubes.

Inventors: ARISI, SERGIO, PARMEGGIANI, ALDO
Applicants: CISE- CENTRO INFORMAZIONI STUDI ESPERIENZE S.P.A.
Application year: 1984
Main classification: G01K1
IPC codes: G01K1