The behaviour of the natural oxide of MANET as permeation barrier under cyclic loads: Self-healing

A gas permeation technique has been employed to determine hydrogen permeati on rates for oxidised tubular MANET (MArtensitic for NET) specimens under c yclic tensile loads. The results obtained over the temperature range 400-87 3 K and for driving pressures of 100 kPa indicate a permeation reduction fa ctor (PRF) of up to 100. Similar measurements performed under cyclic tensil e loads (220 MPa 35% UTS, cyclic rate 10 min/cycle) resulted in a PRF of on ly 50. However, continuous measurements under tensile cyclic load, i.e. the sample was kept in contact with the hydrogen (with similar to 1000 ppm H2O ) for an extended period, has shown a recovery of the initial PFR implying the possibility of barrier self-healing. (C) 1998 Elsevier Science B.V. All rights reserved.