Hot Extraction of Diffusible Hydrogen and Its Measurement Using a Hydrogen Sensor

Abstract

Diffusible hydrogen measurement in welding consumables using a Nafion®117-based Proton Exchange Membrane Hydrogen Sensor (PEMHS) has been carried out successfully at room temperature. The same sensor has now been used for measuring diffusible hydrogen by the hot extraction method. With this objective, a chamber for hot extraction of diffusible hydrogen was designed and fabricated which could be heated to a maximum temperature of 500 °C, while the chamber itself is maintained at ambient temperature by water cooling. The chamber has an inlet and an outlet for argon purging and pressurization. For this measurement, weld specimens were prepared based on ISO 3690, the standard method for diffusible hydrogen measurement, by depositing cellulose, rutile and basic coated welding electrodes (having diffusible hydrogen content ranging between 3 and 31 ml/100 g of deposited metal) on standard mild steel specimen by manual metal arc welding. After preparing the weld specimen, it was transferred to the hot extraction chamber. The chamber was subsequently flushed and filled with argon to a known pressure level and then heated at 400 °C for 30 min for the collection of hydrogen. The concentration of hydrogen in the chamber was measured using the sensor. From the volume of the chamber, the pressure of the gas inside and the mass of the weld metal, the diffusible hydrogen content in the deposits was estimated. Measurements were also repeated using the standard Mercury Method. One-to-one correlation between these two different methods of measurement was obtained. The statistical accuracy of the results obtained with the new Hot Extraction-PEMHS Method was re-confirmed by the t-Test. Further, the hydrogen content obtained with this new method was also compared with the hydrogen content obtained by Thermal Conductivity Detector (TCD)-based Hot Extraction Method (HMAT 2500 Analyzer). This paper presents the development of the system for hot extraction of diffusible hydrogen and its subsequent measurement using the sensor, the results obtained and the possible application of the systems for studying hydrogen evolution from the weld samples.