WHAT IS THE DIFFERENCE BETWEEN A350 LF2 AND A350 LF6 CL.2 1

[ARASH54]

Dear Engineers

Our company is EPC contractor of for Gas Compressor Stations that Des. Press.=1436 Psi and Des. Temp.=-15/83 C .
Oue design for material of Ball Valve Bodies were A350 LF2 but MC company chenged the material to A350 LF6 CL.2 .At first What I'm looking for is the difference between these two grades of A350 and then ,is it possible to use A350 LF2 or not ? because as you know the price for A350 LF6 CL.2 is more expensive than LF2 (about 20%).

Thanks

 

[Ashereng]

Metal isn't my strong suit, but I just noticed you are using low temp steel, and your temperature range is -15 to 83 degress C. Do you need low temp steel?

Isn't the primary difference between LF2 and LF6 the temperature? LF6 is good to a lower temperature?



"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[metengr]

SA-350 Grade LF2 Class 1 is required to have 15 ft-lbs impact energy at -50 deg F, (LF2 Class 2 is required to have 20 ft-lbs at only 0 deg F)

Grade LF6 Classes 1 and 2 are required to have 20 ft-lbs at -60 deg F.

You also need to evaluate the strength requirements (there are differences). I suggest you review this specification carefully.

 

[Ashereng]

metengr,

At -15 - 83 °C, is low temp steel required?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[metengr]

Ashereng;
No. If you go to ASME B16.34 (Standard Specification for Valves...), most of the service temperature ranges are -20 deg F to higher temperatures. Both A-350 grades (LF2 and LF6 Class 1) belong to the same material group 1.1. However, the LF6 Class 2 belongs to Material group 1.2.

The pressure/temperature ratings are slightly different between material groups in B16.34, so this needs to be reconciled.

 

[Cockroach]

MetEngr is correct with the Notch Toughness requirements for ASTM A350 LF2 and ASTM A350 LF6 Class 2 materials.

Some of the mechanical properties are as follows:

ASTM A350 Properties
Tensile (ksi) Yield (ksi) %EI %RA Hardness
LF2 Class 1/2 70-95 36 22 30 197 max
LF6 Class 1 75-100 60 20 40 197 max

Your temperature ratings are also correctly stated by MetEngr. Clearly there are differences in strength(s).

Hope this helps.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[Ashereng]

So, if low temp is not required, he can use A105? Which is even cheaper than A350 is it not?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[ARASH54]

Dear Engineers
Thanks for your replies ,
But I don't have enough reason to not applying LF6 cl.2 for Ball Valve bodies !I am looking for a technical reason to apply LF2 that is cheaper in price .I don't know why MC company advises to use LF6 cl.2 !

 

[metengr]

Oue design for material of Ball Valve Bodies were A350 LF2 but MC company chenged the material to A350 LF6 CL.2

If you are a typical EPC organization, go back to company MC and have them decide on their preference. As you can see, there are differences. If this is a ball valve body, you need to refer to ASME B16.34 for reference. As I stated before, if you compare the pressure/temperature ratings for these two valve material classes, there are differences.

If you are attempting to obtain the lower price material (Grade LF2) to increase profit, run this by your client (MC company). We have provided you with all of the necessary technical information.

 

[Ashereng]

ARASH54,

As metengr mentioned, you may not even need low temp steel.

If you can go with carbon steel, you will get greater savings.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[stanweld]

You have not stated whether MC company is the valve manufacturer or owner/operator.
If MC is the valve manufacturer: it may be "upgrading" its materials to satisfy other customers needs. Due to joules-thompson cooling effects during decompression, some owner operators and engineers have specified the -60F design criteria. Also his cost may be cheaper due to reductions in weight permitted by the use of the stronger material. If the manufacturer changed his materials after award of the purchase order, additional charges need not be paid by your company or the P.O. contract may be null and void and you would be free to search elswhere for another valve manufacturer.

If MC is the Owner, he may designing for joules/thompson cooling and you would be able to charge extra for its Change to the contract.