Temp and H2 Embrittlement

[EngineerPhil]

I am wondering if there is a temperature at which H2 embrittlement starts?

I have a vessel or test flat ened cylinder which I use to pressure test parts at ambient and at elevated temps. The material is phosphated AISI 4145 with a yield greater than 110k psi. There are no welds as the end caps are like flanges and screwed on with stub acme threads. i have some small port holes about 1/4" that are used to fill the vessel. The vol is 10 litres max and the design pressure is 14.5k psi.

I want to know if it would be safe to test at 320°C. I had designed the vessel for testing at a max of 200°C and 11.6k psi, and hadn't really considered H2 embrittlement. Do I need to worry about this now at 320°C.

I think know what H2 is but can't find anything that says if AISI 4145 is susceptible to it or not and if so what temps to whatch out for.

Anyone have any ideas?

Phil.

 

[ijzer]

According API 941 carbon steel at a temperature of 320 Deg. C can be used up to a Hydrogen Partial pressure of about 120 psi.

 

[kenvlach]

Hi Phil,

Briefly, if there isn’t any damage to date, and if you don’t introduce hydrogen, heating is not a problem.

First, ijzer’s info may not apply as 4145 is an alloy steel. Except for lacking Ni, 4145 is similar in composition to 4340 which is so vulnerable to H-embrittlement that when heat-treated to 51HRC-54HRC it is used for testing per ASTM F519.

http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/REDLINE_PAGES/F519.htm?L+mystore+tsah7642

Second, what does “yield greater than 110k psi” mean? How much greater??? Hardness?
An ultimate tensile strength of 110 ksi corresponds to ~ RC 20 (per ASTM A370), which is low enough that H-embrittlement relief is not required after electroplating.

Third, there doesn’t seem to be a hydrogen source. Earlier,
pressure and temperature
thread794-55968
you mentioned that “The medium is hydraulic oil with a max temp of 300°C.”
If the hydraulic oil is stable at temperature, and there is no other source such as acid or cathodic reaction, there doesn’t seem to be a hydrogen source. H-relief bake-out per plating specifications is conducted at about 190^oC, so your PV should be quite free of hydrogen by now. Ergo, you should not have a H-embrittlement problem.

Still, a blast shield would be a good idea whenever pressurizing.
Cheers,
Ken

 

[EngineerPhil]

Many thanks Kenvlach and ijzer,

Perhaps I don't inderstand H-embrittlement completely.

Kenvlach, the oil is quite safe up to 350°C and the hardness of the steel is typically 321-302 Brinell Hardness (HB) with a UTS of typically 145k psi but the spec says 4145 is really 135k psi.

There is no other medium in contact with the test vessel.

The vessel is contained within in a test chanber and the walls are clad with 6mm steel sheet and 6" concrete blocks. I feel quite safe.

Many thanks for your inputs and valuable suggestions,

Thanbks again,

Phil.