WIKA is able to ensure the suitability of the respective products for the application with a series of performance tests in the company's own testing facilities.
Dye penetrant test
Helium leak test
Pressure / stability tests
Dye penetrant test
A dye penetrant test in accordance with DIN EN ISO 3452-1 or SNT-TC1A makes fine surface cracks and porosities visible on weld seams. The affected surface is first cleaned and then sprayed with a contrast agent (red or fluorescent). Due to the capillary effect, this agent penetrates into any imperfections. After cleaning again, a developer (white) is applied, which extracts the contrast agent from hairline cracks and similar openings and enables easy error assessment through the colour contrast.
With an X-ray test in accordance with ISO 17635 or ASME Section V/Article 2, for example, the full penetration weld seams of a thermowell are examined for irregularities such as cracks, cavities and insufficient bonding. Since dimensions < 0.5 mm are involved here, up to five X-rays are required depending on the thermowell. In the case of a thermowell, an X-ray test can also be used to document the centring of the hole. For this purpose, two shots of the thermowell tip, rotated through 90°, are required.
Helium leak test
Helium 4.6 is used in leak tests with tracer fluid in accordance with DIN EN 1779 (1999)/EN 13185. This method is considered the most sensitive of its kind, it detects even the smallest leaks. Two test methods can be followed: An integral test determines leak rates, for example 1x10-7 mbar * L/s. A test with a spray probe, on the other hand, enables a leak to be localised.
Ultrasonic testing in accordance with DIN EN ISO 17640 is also suitable for examining full-penetration weld seams and similar situations. For this, the reflections of a radiated ultrasound signal are measured at the interfaces of irregularities. Beforehand, the ultrasonic device is adjusted with a reference body in order to determine the position of the irregularities. Like X-ray testing, this method can be used to verify the centring of the hole in thermowells. To do this, the wall thickness of the thermowell is measured.
PMI test / Positive material identification
The Positive Material Identification or PMI test proves which alloying constituents are present in the material. The following methods are common: With Optical Emission Spectrometry (OES), an arc is ignited between the surface and the test device, the spectrum of which provides qualitative and quantitative information about the material elements. This test does leave a characteristic burn mark on the workpiece. On the other hand, X-ray fluorescence analysis (XRF) doesn't leave any damage on the surface. In this process, the X-rays excite the atoms of the material to emit radiation. Their wavelength and intensity in turn reflect the proportion of the components in an alloy and their concentration.
Pressure and stability tests
The hydrostatic pressure test is a pressure and stability test of the components of a thermowell following AD 2000 code of practice HP30. For the test, the thermowell is clamped into a test device and subjected to a defined test pressure at room temperature for a certain period of time, for example, three minutes. In general, a distinction is made between the outside and inside pressure test. Typical pressures for this are 1.5 times the nominal pressure of the flange (external pressure) and also 500 bar (internal pressure).