Abstract: The influence rule of air environment pressure on all position primary welding parameters and welding quality under hyperbaric environment is investigated. The investigation shows that the environment pressure has some effect on weld penetration. Primary welding current of downhand welding decreases linearly with the ambient pressure increasing from 0.1 MPa to 0.7 MPa; Primary welding current of overhead position welding and upward welding in the inclined position decreases greatly with the ambient pressure increasing from 0.1 MPa to 0.3 MPa and then changes little afterwards. Primary welding current of downward welding in the incline presents lenitive descent trend with the ambient pressure increasing from 0.1 MPa to 0.7 MPa. Ambient pressure has great affection on mechanical property of welding joint, tensile strength and impact toughness of joint decrease with the ambient pressure increasing, while the hardness of HAZ and welding seam increase.

Key words: All-position, High-pressure, Mechanical property, One side welding with back formation, TIG, Amplitude frequency curve, Instantaneous amplitude, Instantaneous frequency, Signal decomposition, Hilbert transform