CRACKING only in ER-80S B2 exposed to H2 2

[mcisajp]

I am looking for reference microstructure that relates hydrogen attack or embrittlment in ER-80S B2 filler metal that was TIG weld to a fillet weld between AISI 4140 bar and 1.25Cr-.5 Mo plate . This material was HT and the final Hardness was less than 200 BH.... Now a fail sample is showing 45 HRC and martensitic-bainitic structure.... Other sample no failed is showing perlite + ferrite and around 88 HRB. There is cracking branched and in different directions only in the weld filler metal, which is exposed as well as the base and the HAZ to a H2 and high temp condition ( up to 860 C in gas side if refractory fails and 319 C on a water side).
Please let me know of any web site were I can find information or if you have information, please send it to me

Regards

 

[metengr]

Several questions related to your post;

1. In the weld deposit that contained cracks, what was the preheat temperature?

2. What was the preheat temperature used for the second sample that did not fail?


Based on the hardness you reported of 45 HRc, it would appear that you did not perform a post weld heat treatment -correct? Was the second sample that did not fail subjected to a post weld heat treatment?

Even with the GTAW process, hydrogen embrittlement can occur in the weld metal and/or in the weld HAZ in base metals that are carbon steel (with a carbon content above 0.35%) or low alloy steel from hydrogen dissolved in the weld wire or from shielding gases. Hydrogen embrittlement cracks can be transgranular in the weld metal or intergranular in the base metal HAZ (containing a coarse grained martensitic structure), and can be subsurface or can propagate to the surface as a means of relieving dissolved hydrogen.

The American Welding Society has a web site (aws.org) that contains various technical papers (for free) on hydrogen embrittlement of welds.

Also, you can perform an internet search with "hydrogen embrittlement of welds", which will turn up many web sites with information.

 

[metengr]

Here is an interesting technical paper on hydrogen-assisted cracking related to Cr-Mo weldments;

http://www.iisc.ernet.in/~academy/sadhana/Pdf2003JunAug/Pe1120.pdf

 

[mcisajp]

I will be extensive:
Cracks are seen only in the weld remained in the plug . The dia 1.5-inch cylindrical plug does not shown any damage. Also, some defects were detected with PT in adjacent area of the tube sheet. In addition, the cracks w/o etching are starting and parallel to the fracture plane.
The plug that failed was made of AISI 4140, but microstructure after being in service is basically martensite with 53 HRC.
The second sample is a plug also made of AISI 4140 . This was in service and was removed for accessing for inspection. It did not fail and the microstructure found was a typical perlite in ferrite with an 88 HRB.
A resume of welding parameters used was as follow for Base metals 13CrMo44. ( P12, 1 Cr- .5 Mo ) and AISI 4140:
1. Surface and PT to defect free.
2. Bake to 350-400 ° C for 3 hr.
3. Weld :
a. Process TIG,
b. Filler dia 3/32 “ , ER-80S-B2
c. Filet weld with 8-9 mm. throat
d. Preheat to 150-250°C
e. Max. Interpass 250°C.
4. Heat treat at 725-750 °C for 2 Hr.
5. Hardness after cool down . This was found in less than 200 BHN in all places measured. TT curve complied with requirement.

One mayor service difference among the 2 plugs was that in one case, the one that did not fail and hardness was 88 HRB is that the refractory for protecting was a dense casting with a Incoloy 800 plate to further protect from gas erosion. For the second, the failed on the weld one that finish with up to 53 HRC, the refractory use was an insulating type with the protective INCOLOY 800H plate, but on places where the plug were the hole of the tube plugged was not covered and the insulating one got exposed . This it what it is believed caused the metal to probably change the structure since de hot face can go up to 873 C and there is H2 present at 131 psi partial pressure. One of the question is why only on the weld ???.
I hope this can give METENGR AND ALL OF YOU an information for further comments.

Regards,

 

[metengr]

Ok. After reading your second post, I believe what you have indicated is that the first plug weld that contained cracks was properly preheated and PWHT and placed into service.

Considering your operating temperature in service and your statement regarding loss of refractory, it appears that you had exceeded the lower critical transformation temperature of the weld metal and plug material in service resulting in the formation of martensite. This would explain the 53 HRc hardness, observation of martensite and the 45 HRc hardness in the plug HAZ in your earlier post. The other welded plug was adequately protected from service temperatures.

Untempered martensite (which is what you had formed in service) is very susceptible to hydrogen assisted cracking (HAC) or hydrogen embrittlement. The reason that the weld contained cracks versus the plug material could be based on the number of hydrogen traps in the weld deposit versus the plug base metal. Hydrogen assisted cracking develops at locations of high tensile stress. Welds contain coarse grains and inclusions which can act as natural hydrogen traps in service. Depending on the cleanliness of the weld metal and level of residual stress or service stress, this could explain why hydrogen assisted cracking developed preferentially in the weld metal versus the HAZ.

 

[SMF1964]

Try the following:

http://www.twi.co.uk/j32k/protected/band_3/jk45.html