Grain Size Requirement for Tube Material

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Austenitic stainless steels have high ductility, low yield stress and relatively high ultimate tensile strength, when compare to a typical carbon steel.

A carbon steel on cooling transforms from Austenite to a mixture of ferrite and cementite. With austenitic stainless steel, the high chrome and nickel content suppress this transformation keeping the material fully austenite on cooling (The Nickel maintains the austenite phase on cooling and the Chrome slows the transformation down so that a fully austenitic structure can be achieved with only 8% Nickel).

Heat treatment and the thermal cycle caused by welding, have little influence on mechanical properties. However strength and hardness can be increased by cold working, which will also reduce ductility. A full solution anneal (heating to around 1045°C followed by quenching or rapid cooling) will restore the material to its original condition, removing alloy segregation, sensitisation, sigma phase and restoring ductility after cold working. Unfortunately the rapid cooling will re-introduce residual stresses, which could be as high as the yield point. Distortion can also occur if the object is not properly supported during the annealing process.

Source: http://www.gowelding.com/met/austenitic.html

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I don't know if it answers your question, or not. You may have to do your own work.

Good luck.

The fact that grain size has an effect on the material properties of crystalline materials (as most alloys are) has been known for a long time - since about 1900.

Grain size is hard to measure for the obvious reason that a section through any given piece of material will cut across the grains in that material at random points - but it can be measured and is often expressed via a series of equations that have a Hall-Petch form.

The document "The Influence of Grain Size on the Mechanical Properties of Steel" at

http://www.osti.gov/bridge/servlets/purl/861397-Tb7pb9/861397.pdf explains that many of the important mechanical properties of steel, including yield strength and hardness, the

ductile-brittle transition temperature and susceptibility to environmental embrittlement can be

improved by refining the grain size. It goes on to say that for the common range of grain sizes that the values of typical mechanical properties increase with the reciprocal root of the grain size.

While it is easier to measure/monitor (say) tensile strength and get an accurate value by a simple tensile test, this is not the case for other important material properties like susceptibility to stress corrosion or fatigue resistance. For these things alloy and grain size, in combination with tensile strength is a "better" control measure for this reason is often required in a specification. preferred.

Here is some more general information regarding how Grain size can influence material and its properties, though not in an ASME code perspective.

http://pmpaspeakingofprecision.com/2010/06/15/5-engineering-aspects-of-austenitic-grain-size/

Milo