Pipe & Fittings - CS vs LTCS 2

[QW Tian]

Dear Community

I noticed that ASTM material for piping carbon steel (CS) and low temp carbon steel (LTCS)are similar in chemical composition and manufacturing process including heat-treatment. However, LTCS has a higher toughness for impact-test at -45 deg C (or -46 deg C).

I am referring to the following piping ASTM material :
Pipes : A106 Gr B vs A333
Forgings : A105N vs A350 LF2
Fittings : A234 vs A420

My query is which elements/factors cause the LTCS to have a higher toughness ?

I would pose a similar query on Metal & Metallurgy Engineering Group.

regards

QWT

 

[1503-44]

See my attached notes on basic steel metallurgy


Please do not make multiple posts; one post per question.

 

[SJones]

https://onepetro.org/NACECORR/proceedings-abstract/CORR19/All-CORR19/NACE-2019-13361/127396

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[weldstan]

It's not just the fine grain melting elements but also forming and heat treatmnt parmeters.

 

[austsa]

In the case of A105N vs A350-LF2, the difference may be material certification only??? However, certification is very important, from compliance and legal perspectives.

 

[georgeverghese]

In modern practice, silicon killed CS and LTCS are the same from a materials perspective. LTCS is tested and certified by the manufacturer/mill and killed CS is not. Some 30-40years(?) ago and before, normal CS was not silicon killed, which was then the reason for many cases of brittle fracture.

You would be taking a risk if you are planning to use plain killed CS as a substitute for certified LTCS these days for lower design temperatures -45degC < T < -20degC, though the risk is much less than a long time ago.

 

[weldstan]

Thank you Steve for the abstract. The very low Mn contents that I beagan to see on A106B mill certs about 2 years prior to my retirement in 2015 were expected to produce very low absorbed energy values at temperatures of 32F and would also be expected to have much lower creep strength at temps above 650F - only time will tell how true this is for power plant piping constructed frrom these steels.

This dicussion, where it appears that some engineers believe that the killed carbon steels are somewhat equivalent to LTCS except for imact testing, is quite erroneous. While the A105N, A106B, A234 and others can be made and often are made to a fine grain melting practice togay, they most often do not have equivalent Mn:C ratio controls, minimimmu S and shape controls and other elementzl controls common to the LTCS materials, in addition to hot forming and heat treatment controls.