After re-reading the original thread, distinuishing HE can be determined, but typically this involves extensive metallurgical/mechanical testing.
Stanweld noted hot-cracking. Typically this would be due to poor workmanship, technique or both by the welder or operator. Wide "weave beads", weld layer and bead thickness are typical examples. Contaminated electrodes, fluxes and coatings (SAW, SMAW or FCAW), welding environment or dampness in the weld area or welding in inclement weather (regardless of the process) and the type (classification) of electrode used (FCAW, SMAW and SAW) are other sources for HE.
I monitored many samples taken after the Northridge earthquake. The testing determined delayed hydrogen cracking (DHC) on a large number of samples. These failures occured usually over long periods of time and loading during other seismic activity, but as Stan noted may be hours. Many specifications now require a delay period before the nondestructive testing of welds, typically 48 hours.
Joint design, QC and welding parameters were also an issue in Northridge.
Also noted by Stanweld was heat affected zone (HAZ) cracking. Underbead cracking (just beyond the HAZ but in the vicinity) was present in a number of samples. These are common in pressure piping and vessels when welding is performed incorrectly wether due to technique, workmanship, incorrect electrode selection or PWHT (or lack thereof).
As noted previously, there is extensive info on this subject if you use your search engines.
