Hydrogen embrittlement characteristics in a weld

[EngineerDave]

Is there any good way to distinguish cracking that is due to hydrogen embrittlement in a weld, relative to cracking from other sources?

I am looking for some characteristics that may help me determine this.

 

[mcguire]

One distiguishing characteristic of hydrogen embrittlement is delayed cracking while hot short cracks would happen at high temperature during cooling. I presume based on that that one would have oxide and one wouldn't ( one the fracture surface).

 

[CWIC]

There are many methods of determining H.E. cracking. Use your search engine and you'll be surprised how much information is available on the web regarding this subject, more than one post or reply could provide.

H.E. conditions can definitely be distinguished from other modes, sources and causes of cracking or failure. You may want to try the Welding, Bonding and Fastener forum with your query, there are some very sharp people who reside there.

 

[stanweld]

Hydrogen cracking can occur in the weld metal or HAZ and can be transverse to the welding direction or in the welding direction or variations thereof. Hydrogen cracks in steels generally occur below 250 F and may take many hours to develop at ambient temperature.

Generally but not nearly always, hot cracking occurs in the center of the weld (last material to solidify)in the welding direction and is immediately visible upon solidification.

 

[Rich2001]

See faq330-85 for general information on WELD CRACKS

 

[CWIC]

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.