To determine the net hydrogen contents produced by the electrode’s flux, this test first requires the electrodes to be used to produce welds of pre-determined length under laboratory controlled temperature and humidity. The welds are carefully kept at sub-zero temperatures during post-welding processing to prevent loss of hydrogen via diffusion, up until they are loaded into a gas chromatography chamber. The coupons are heated up to a pre-determined temperature and held for a fixed duration to release the diffusible hydrogen gas within the weld. By virtue of the difference in gas molecular weight, the hydrogen gas collected can be separated from the equipment’s inert carrier gas and quantified.
The determination of diffusible hydrogen content via Gas Chromatography is primarily used as a characterization test for electrode manufacturers to certify a batch of electrodes as being low hydrogen contents according to AWS electrode specifications but can be specified as a more realistic batch verification test for end users to determine whether a stored batch of electrode is still fit for purpose as part of a quality control or troubleshooting process.
Emission spectrometry is a comparative analytical method in which a small amount of surface material is removed from the specimen. Recent developments in sensors and microelectronics have produced transportable systems that can be used on or adjacent to production lines. In some systems, light from the spark discharge is carried by fiber optics to the sensors, where the wavelengths and intensities of the several spectrum constituents are detected and measured. Photomultipliers are used with diffraction gratings to measure the intensities of preselected analytical lines in the spectrum. The numerical results are displayed in digital form on readouts or printed out in hard copy, or both.
At PTS, our OES method of chemical analysis for steel and stainless steel products are accredited to SINGLAS, with the ASTM test method of E415-2008 and E1086-2008 respectively.
Sulphur dioxide(SO2) absorbs infrared (IR) energy at a precise wavelength within the IR spectrum. Energy of this wavelength is absorbed as the gas passes through a cell body in which the IR energy is transmitted. All other IR energy is eliminated from reaching the detector by a precise wavelength filter. Therefore, the absorption of IR energy can be attributed to only SO2 and its concentration is measured as changes in energy at the detector. One cell is used as both a reference and a measure chamber. Total sulphur, as SO2, is monitored and measured over a period of time.
Carbon dioxide(CO2) absorbs infrared (IR) energy at a precise wavelength within the IR spectrum. Energy of this wavelength is absorbed as the gas passes through a cell body in which the IR energy is transmitted. All other IR energy is eliminated from reaching the detector by a precise wavelength filter. Therefore, the absorption of IR energy can be attributed to only CO2 and its concentration is measured as changes in energy at the detector. One cell is used as both a reference and a measure chamber. Total sulphur, as CO2, is monitored and measured over a period of time.
At PTS, our test method includes ASTM E1019-2008.
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In general, the LECO ONH Determinator, uses the inert gas fusion technique. The technique is to fuse the sample in a high purity graphite crucible inside a furnace by taking it to very high temperatures (~3000°C) in an inert gas environment to efficiently release the target gases from within the sample. The graphite crucibles are effectively resistors that supply the heat necessary to fuse the sample, as well as Carbon for the reduction of Oxygen in the sample. An inert carrier gas, purified Helium gas, sweeps the liberated analyte gases out of the furnace, through a Mass Flow Controller, and to a series of detectors. Oxygen present in the sample reacts with the graphite crucible to form CO and CO2, which are detected using non-dispersive infrared (NDIR) cells. The gas then flows through a reagent heater where the CO is oxidized to form CO2 and H2 is oxidized to form H2O. The gas then continues through another set of NDIR cells where H2O and CO2 are detected. These analytes are then scrubbed out of the carrier gas stream. The final component in the flow stream is a Thermal Conductivity (TC) detector which is used to detect nitrogen.
Inductively Coupled Plasma – Optical Emission Spectrometry (ICP-OES) is a sensitive analytical technique, which is widely used for the determination of trace elements. In optical emission spectrometry (OES), the sample is subjected to temperatures high enough to cause not only dissociation into atoms but to cause significant amounts of collisional excitation (and ionization) of the sample atoms to take place. Once the atoms or ions are in their excited states, they can decay to lower states through thermal or radiative (emission) energy transitions. The intensity of the light emitted at specific wavelengths is measured and used to determine the concentrations of the elements of interest.
The sample is usually transported into the instrument as a stream of liquid sample. Inside the instrument, the liquid is converted into an aerosol through a process known as nebulization. The sample aerosol is then transported to the plasma where it is desolvated, vaporized, atomized, and excited and/or ionized by the plasma. The excited atoms and ions emit their characteristic radiation which is collected by a device that sorts the radiation by wavelength. The radiation is detected and turned into electronic signals that are converted into concentration information for the analyst. A representation of the layout of a typical ICP-OES instrument is shown in the figure below.
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