concluded that the X70 base metal exhibited a lower FCGR than the HAZ from a submerged arc weld of two plates for the same conditions, where the specimens were subjected to saturated H2S in solution.
There should be no measurable difference in FCGR, either in air or in hydrogen gas, because both of these waveforms provide short time durations at the peaks .
Data on cycle count, crack mouth opening displacement (CMOD), external force, and internal force were collected for 5 cycles out of every 200 cycles, and these values were used to calculate [DELTA]K and a to generate graphs of FCGR (da/dN versus [DELTA]K, where N is the number of cycles).
For a detailed account of the uncertainty of the FCGR measurements presented here, see Ref.
The results for FCGR in hydrogen gas at a pressure of 34 MPa for the weld fusion zone, associated HAZ, and base metal from the four pipeline materials studied are shown in Fig.
8, followed by a rapid increase in the FCGR over a short span of [DELTA]K.
The FCGR in Region 2 is governed mainly by crack tip stress intensity levels, but can be affected by testing variables such as stress ratio (R = [K.sub.min]/[K.sub.max]) (14).
For Type A, the FCGR in Region 2 may be higher in hydrogen environments, compared to the rate in inert or air environments.
The FCGR were determined over stress intensity ranges between 20 MPa [m.sup.1/2] and 70 MPa [m.sup.1/2].
The FCGR at low [DELTA]K ([approximately equal to] 22 MPa [m.sup.1/2]) deviated only slightly between specimens tested in air and hydrogen, but at higher [DELTA]K ([approximately equal to] 40 MPa [m.sup.1/2]) the rate in hydrogen increased by almost twenty times the rate in air.
Figure 6 shows the effect of R on FCGR for X42 steel at a [DELTA]K of 10 MPa [m.sup.1/2].
It was found that the ratio of FCGR in hydrogen to that in nitrogen increased as a power function (power of 0.36) of the hydrogen partial pressure, as shown in Fig.