T/P 23 & ASME Code Case 2199 1

[Guest102023]

I have managed to virtually purloin a copy of the original code case, but I know there have been a series of successive versions, up to 2199-5 if I am correct.

My question is whether these revisions are merely renewals or revisions; and if the latter, what was the nature of the changes? I saw a murmuring in CCJ that chemistry was revised.

 

[metengr]

The most recent code case revision (5) relates to a modification in chemistry for Grade 23. The change in composition relates to the deliberate addition of Ti, and several other minor adjustments. The original problem with this material is that tube suppliers that used the previous code case could not achieve the desired hardness, after cooling but before tempering. This material after austenitization should achieve a bainitic-martensitic microstructure with little to no ferrite. Ferrite was confirmed to be present in several heats which resulted in the lower as-quenched hardness before final tempering. Several batches of this Grade 23 went on to customers as final tubing.

 

[Guest102023]

Searching through previous threads there was a long discussion a couple of years back about Ti and properties of T23. I want to add a few comments:

(1) Boron activity is predicted from the Ellingham diagram for nitrides (if anyone has a good sample I would love to get it).

(2) Boron is known to have a powerful effect in lowering free energy at grain boundaries. In the case of CSEF steels, it controls M23C6 carbide growth and coarsening, which is detrimental to creep properties.

(3) Ti would be added to T23 because of its greater affinity for N. Some N is unavoidable in any steel, sometimes it is added intentionally. Only free B is 'effective', so it needs to be protected from N.

(4) I suspect B also acts in T23 to suppress ferrite formation (as in HSLA steels), thereby promoting bainite. This would be consistent with your comments re: low hardness in T23.

 

[kalmari]

Note that this latest revision CC2199-5 has a lot of requirements for heat treatment after forming depending on the strain. These haven't been in earlier revisions.

 

[metengr]

That is correct because we had no creep data to compare below 10% cold strain , and creep data from 10% and above cold strain from V&M showed a significant reduction in creep strength.