Thermocouple in the thermal power plant set box, pipe widely used, it set box and pipe welding temperature casing, placement thermocouple, the temperature set box and real-time data acquisition. Set box and usually at a high temperature, high pressure, temperature thermocouple sleeve fillet weld under tremendous loads, and thermowell Most of the fillet weld dissimilar steel welds prone welding defects. Has been found that a number of thermal power plants thermocouple casing fillet weld leaks, cracking phenomenon, so the temperature thermowells fillet Welding Material quality detection is very important.
1 thermocouple sleeve fillet weld several types of quality control
The thermocouple connector type for corner joints, weld type in accordance with the type of groove into the saddle type and two plug-in, plug-weld can be divided into semi-insert and full insertion of two. Fully inserted weld in accordance with the design requirements which full penetration weld, semi-insert allows incomplete penetration. Casing fillet weld ultrasonic testing method based on a different type of groove and insert type thermocouple of the same.
The 2 thermocouple sleeve fillet weld quality ultrasonic detection
2.1 saddle fillet weld quality ultrasonic detection
Saddle fillet weld thermocouple casing pipe seat height is generally 20 ~ 30mm, diameter of about 100mm, can be inclined probe thermocouple tube seat Welding Wires scanning, according to the temperature measuring thermoelectric Even casing pipe seat height, usually with a wave or secondary wave Weld scanning.
2.1.1 Probe selection: In order to better scan found the root of the weld should be small wafer probe testing. Select probe k value of the primary wave scan found at least the end of the weld point O, can be calculated based on the geometric conditions of temperature thermocouple thickness of the tube socket weld width.
2.1.2 Engineering detect instances
A 600MW unit reheat steam pipe temperature measurement thermowell fillet weld, the weld groove type saddle, tube socket thickness b = 25mm, the weld height of h = 20mm, H = 65mm detection STAV-ELEY digital ultrasonic flaw detector, the probe is 2.5P66K2.5 (by measuring probe forefront 6mm). GB11345-89 testing standards.
The testing method using the direct method and the reflection method, Class B test to determine the detection sensitivity, and that as a flaw detection sensitivity 30mm at Φ3 × 40-16dB. If you consider the coupling compensation 3dB, the detection sensitivity for Φ3 × 40-19dB. After testing, h = 12.5mm at found a defect wave equivalent Φ3 × 40 +2.5 dB, 6dB length measurement method measured the size 12mm, failed. Anatomy, the discovery of the defect as a slag.
2.2 plug-in, with full plug-in thermocouple casing half the quality of the fillet weld ultrasonic testing
Semi-2.2.1 plug-in thermocouple casing fillet weld detection method
General semi-insert thermocouple casing diameter 38mm, internal thread, not from the casing side testing. Therefore, the half-insertion seam and fully inserted into the seam should be in the side of the collection box detection. The probe K value according to the height of the weld was seized to reference DL/T820-2002 standard selection.
2.2.2 full plug-in thermocouple casing fillet weld detection method
Full plug-in thermocouple sleeve fillet weld probe surface and probe K value selection with the same plug-temperature thermowell fillet weld detection.
Plug-in 2.2.3 half full plug-in fillet weld detection difficult thermocouple casing
Semi-plug-and full-insert the thermometer thermowell fillet weld testing difficulty lies in the difference between testing process structure the echo and defects wave.
Half insert fully inserted thermocouple casing within the hole diameter of about Ф6mm, when the probe around the weld inspection, the reflected echo may occur within the hole. Shown in Figure 6, when the probe around the Weld found p position, ultrasonic and the reflection angle of the inner hole of the exactly rectangular. Casing inner bore of vertical reflection can occur at this time, the vertical reflection wave signal to the inner hole in the detector can be observed on the display. Generally, when the probe is located in the radial direction, the maximum reflection amplitude. In this case, by calculation, shows that the probe being used inner bore reflector occurs collection box outer wall along its leading edge to the casing the distance of the outer wall P = R × (90-arctanK)-l0-δ (wherein, R is the outer diameter of the collection box , K probe the value of K, l0 for probe frontier value, δ casing radius), field weighed reflection occurs probe forefront distance away from the casing outer wall, contrast can determine whether the inner hole reflection. Can also be used a probe (such as K1 and K2 or K2, K2.5) of the two K values with the sweep, Generally, because of its particularity of the angle of reflection, the reflected wave of the inner bore does not sweep in two different K values probe The CHA simultaneously exist.