Hydrogen Bakeout Monitoring

Welding of steel is often preceded by a hydrogen bakeout, also known as a pre-weld hydrogen bakeout. The procedure is deemed necessary when steel has been in ‘hydrogen charging service’, basically circumscribed by the applications for hydrogen flux monitoring.Such steel may contain significant concenrtations of trapped hydrogen. During welding, the hydrogen is concentrated near the weld pool.On cooling, the hydrogen can then cause stress oriented hydrogen induced cracking. Therefore the object of a hydrogen bakeout is to remove hydrogen which might cause SOHIC.

The objects of monitoring the bakeout are:

  • to confirm whether a bakeout is necessary, for future reference
  • to prevent weld failure by ensuring sufficient hydrogen bakeout
  • to save several hours of turnaround time if and when hydrogen flux monitoring indicates a hydrogen bakeout to be complete

A Hydrosteel bakeout flux kit is offered by Ion Science for bakeout monitoring.The technique engages HT-S probes attached to the bakeout perimeter at approximately 1 m intervals.A bakeout is deemed complete when the bakeout temperature has been reached, and when the flux readings at all positions have not exceed, or decreased below, 1000 pL/cm2/s.