Method of hydrogen loss reduction for TDS apparatus

Abstract

Hydrogen embrittlement is a major concern for many engineering applications, especially the steel industry. Steels during production and in service are susceptible to cracks and fissure as a result of the effect of hydrogen diffusion and trapping in them. The use of high strength steels by the automobile industry, the search for suitable materials for nuclear applications and the selection of materials for hydrogen storage tanks form strong basis for research on the effect of hydrogen on metallic materials.

There are many technics for the investigation of hydrogen concentration, trapping behavior and embrittlement mechanisms. Thermal desorption spectroscopy (TDS) is a technique reliably used to investigate hydrogen interaction with metallic materials. With this technique the samples are measured in an ultra-high vacuum chamber (UVH). The specimen are first loaded in an air-lock, pumped to an intermediate vacuum pressure, to prevent the contamination of the UHV chamber.

Hydrogen escape from specimens during air-lock dwelling time in the interim of the TDS procedure was investigated. The hydrogen loss during TDS procedure for Ferritic steel ASTM UNS S43940, as-supplied ferritic- martensitic steel, H-charged ferritic-Martensitic steel and AISI 304 austenitic steel was measured. The specimens of each material were measured consequently with an air-lock dwelling time of 10, 20, 40 and 60 minutes.

The results revealed that for 60 minutes air-lock dwelling time before measurement, The H escaped as a percentage of total hydrogen concentration is 15.9%, 64%, 136%, 13% for measured ferritic steel, as-supplied ferritic-martensitic steel, H-charged ferritic-martensitic steel, and austenitic steel respectively. The biggest hydrogen escape for all specimen occurred during the first 10 minutes of air-lock dwelling time. To reduce the extensive loss of hydrogen, the temperature of the specimen must be reduced.

A vacuum compatible cooling system was built for a new TDS apparatus. The cooling system comprises of A heat sink, cooling loop coupled with a refrigerator and four modules of TE-65-0.6-0.8 micro-thermoelectric coolers (TEC). The cooling system cools to -13.4ºC in 10 minutes at a vacuum pressure of 10-2 mbar.