Brittle Failure of Vessels 1

[djack77494]

The most excellent (but now closed) thread, number thread135-145412 , contained a discussion about the depressurizing of a tank containing a liquified gas (CO2). In the thread, Mr. Montemayor presented a scenario in which a full depressurizing of a vessel caused the steel temperature to drop to the contained fluid's boiling point (-78oF in that case). He then implied that the tank was essentially useless, having been rendered so by exposure to low temperatures.

Some unanswered questions followed about whether the steel's properties weren't restored when it returned to ambient temperature. A second question arose concerning the possibility of restoring the vessel through some means such as stress relieving. Can anyone address these issues?

 

[SJones]

Mr Montemayor quotes himself as having a 'Chemical' background which would account for his not understanding the brittle fracture degradation mechanism too well. Your best start would be to study Appendix L of API Publication 581

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[MJCronin]

djack...

Suggest that you repost in the Boiler & PV forum.

There are many engineering texts available that describe the dangers of brittle failure (fracture) in boiler and pressure vessel operations.

Most of the design codes (incuding ASME VIII)force both the designer and operator to ensure that the materials selected do not operate in the brittle range. Some materials, of course (austenitic stainless steels) do not have a brittle range.

-MJC

 

[MJCronin]

I know it doesn't answer the question, but here are some websites with information devoted to brittle fracture:

http://en.wikipedia.org/wiki/Fracture

The field of knowledge that is devoted to these effects is called "Fracture Mechanics"

You could post your question on another website that may be much better equipped to answer it:

http://www.hghouston.com

(The Hendrix group)

Please complete the thread and let us know what the final answer is..

Regards:

-MJC

 

[JOM]

Hi MJC.

I'm sure the tecnical understanding of brittle fracture resides in the forums you've suggested, but I think it is important that knowledge of the phenomenon of brittle fracure be widely known.

Operational people need to know of it. It shouldn't be secreted away in a specialist arena.

I too would like to know the answer to the original query -does a steel vessel satisfactorily recover from a cold embrittlement excursion, when it returns to warm temperatures? Or has it been permanently damaged?

John.

J.

 

[JoeTank]

JOM,
Steel does not "embrittle" at low temperatures. True it may have lower toughness, but that is a temperature dependednt problem. The steel's metallurgy is not permanently altered. When the steel warms back up, its just the same as it was previously to the cold temperature excursion.

Joe Tank

 

[SJones]

Brittle fracture is based on a triangle: imperfection size, stress, and material resistance (fracture toughness). For carbon and low alloy steels, fracture toughness is related to temperature, generally reducing with reducing temperature. Whether any damage is incurred therefore depends on whether there are any imperfections of a critical size, whether there is sufficient stress, and whether the fracture toughness of the material, including any welds, is below a critical level. This is the realms of 'fitness for service' as addressed by API 579-1 and BS 7910. This forum is not the place to try and summarise these documents. Interested parties should research them off forum for a better understanding.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04