low temperature magnetic material

[fred01]

I need a magnetic material that is pressure vessel grade suitable down to -40C and complies with the PED requirements particularly for ductility "its bending rupture energy measured on an ISO V test-piece is no less than 27 J" at -40C.
There are some boiler plate grades that are OK but this is for a valve so I need a bar grade rather than plate.

 

[EdStainless]

Do you mean ferromagnetic material? as in a steel.
If you know of an alloy then simply search for that alloy number in other product forms.

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Plymouth Tube

 

[fred01]

Thanks Ed. I do mean steel or steel alloy but I need a suitable pressure vessel material such as ASTM A479 but it needs to be magnetic and ductile at -40C.

 

[btrueblood]

see

http://www.nickelinstitute.org/~/Me...Ni_ResistandDuctileNi_ResistAlloys_11018_.pdf

 

[jwhit]

Since it is for a valve, what about cast grade ASTM/ASME A352/SA352 Gr. LCC? If casting composition and heat treatment is properly controlled it can easily meet the PED criteria and is commonly used for these applications.

 

[jwhit]

To add a thought to using LCC, assuming that you are specifying the material for sub-contract manufacture, I would recommend discussing using of the material or any ASTM/ASME material with your NOBO or RTPO. Since our specifications aren't harmonized standards in many cases, a Particular Material Appraisal is needed to approve it. This may have been done already, but needs to be verified.

 

[weldstan]

A/SA-537
A/SA-516
A/SA-333 Gr 6
A/SA-350-LF2
All of the above can be purchased with impact toughness at -40 C and lower.

 

[fred01]

Thanks weldstan but none of those are for bar.
Thanks jwhit. It looks like I will have to use cast grade. Does the LCC grade have the best magnetic properties (i.e. highest permeability)?

 

[MagBen]

Assuming you are talking about DC permeability (so the resistivity doesnot matter much),the lower the contents of the alloying elements, the higher the DC permeability. so low temeprature austenitic and alloy steels are not good at magnetics. LCC is mechanically a bit stronger than LCB (due to higher Mn?), LCB maybe a better choice in terms of permeability.

 

[jwhit]

If there is any difference in permeability it will be minimal. A lot of foundries, including where I work use the same composition for LCB & LCC, with residual elements and carbon equivalent held to 0.43max which is where you need to be for many of the petro applications. Having said all of that, modifications to the aim chemistry are also readily achieved if you need them for some reason, provided the modifications still fall within the scope of the specificaton.

 

[MagBen]

I am not familar with these grades. if very similar, then why bother assigning two names, LCC vs LCB?

Based on jwhit's statement I agreed with the comments on permeability

 

[weldstan]

You can purchase reforging billet/bar stock as A-350-LF2. One assumes that the bar stock will be used for the stem, which is not considered a pressure part. AISI 8620, purchased with impact testing at -40 C would readily meet your toughness requirements.

 

[jwhit]

Magben,
That is a good question and one I have pondered at times. The same holds true for A216 Gr.WCB and WCC, which are for use at warmer temperatures,that is, above -20F and have the same composition requirements. I had occasion to look at some LCC impact test results today and they ranged between 24 and 40 ft lbs at -50F/-46C.
I believe the forging grade that weldstan referred to is very similar to LCC.