ASME BPVC.II values for ASTM A350 LF3 at low temperature -78 deg F/-61 deg C

[Sol71]

We have a product (hydraulic access fitting and cover) that we as a standard deliver in ASTM A350 LF2, all caluculations are based on ASME BPVC, sec II.
Now we have a case where the customer have specified the the lowest design temperature to be -78[sup]o[/sup]F/-61[sup]o[/sup]C, as the material engineer I have suggested that we might offer LF3 (rated to -101oC)instead to meet the low temperature requirements. The structural department want to do some calculations to show the customer that this is acceptable strenght wise, but they are struggeling to find the corrrect values in ASME II, and now they want me to come up with correct values for their calculations.
I'm not too familiar with ASME, but as I understand the minimum temperature for the material curve is -30[sup]o[/sup]C (-22[sup]o[/sup]F)and hence ASME II do not cover for lower temperatures. Any good explanantions s to why? And also where should I look or point the structural engineers toward for correct values.

Hope anyone can give me some good input here.
Thank you.

 

[SnTMan]

Sol71,I think you have your terminology crossed a bit. ASME Sec II is a collection of material specifications (Part A, Part B) and material allowable stresses and other properties (Part D).

Section II is not a design Code, such that your comment "the minimum temperature for the material curve is -30oC (-22oF)" is just not true.

For the subject material, SA-350 LF3, there are two classes 1 & 2, both impact tested at -101C as you noted, and therefore suitable for use at that temperature. Now, Sec II, Part D lists allowable stress for the design Codes Sec III, Sec VIII, Div 1 & Sec XII as 20 ksi up to 500 F, and a maximum permitted design temp of 650 F. The 20 ksi allowable is also valid for below ambient, i.e. your -78F design temp.

As a note, SA-350 LF2 has the same 20 ksi allowable up to 400 F only and max permitted temps vary between the Sections. Sorry about the unit switch

Not sure why there are two classes of LF3, as they seem to be identical.

These allowables are found in Sec II, Part D, Table 1A, hope this is useful to you.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Geoff13]

Class 1 has required impacts of 15/12 ft·lb @ -150°F.
Class 2 has required impacts of 20/15 ft·lb @ -150°F.

Hardly seems worth defining two classes for such a small difference.

 

[SnTMan]

Geoff13, correct, thanks, I didn't read carefully

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[georgeverghese]

In the European based OpCo I used to work in, LF3, which is 3.5%Ni steel, is not used (this seems to be popular with US oil/gas OpCos though). At LDT <-40degC, the Company choice is lean duplex SS, which is good down to -80degC. Believe the problem with these impact tested low alloy carbon steels is the reliability of the impact test results.

 

[Sol71]

Thank you for the input SnTMan, I will relay the information to the structural engineers.
Just want to clarify that I know that ASME II is not a design Code (and english not my native language so I probably didn't express myself correctly), but the structural engineers are using the values and criteria in there for designs and are now hasseling me to find correct values.

 

[XL83NL]

Why would a structural engineer use stress allowables from a standard that defines a multitude of variables/variable values per material, plus has a different basis for determining these allowables than what would be normal for structural design?

 

[Sol71]

Well I don't know XL83NL, I'm not a structural engineer, I'm a metallurgist not working with these things at all. These structural engineers are located in a different office in a different country and I suspect that their training is not very good, and they are not my responisbility. I only have the information that they send me per email. So instead of just putting out an unecessary question like that, how about giving some constructive input to what they should do?

They want me to give them input on what values to use when doing analysis and calculations for the new material I suggested for the design, and they have gotten completely hung up in the minimum temperature for the material cuve in ASME II. As I said before I'm not at all familiar with ASME as this is not in daily use her at my office and what they are asking for is actually beside my daily work and postion, but at least I'm trying to help them out, since at the moment they do not seem to be able to overcome the problem on their own.

 

[XL83NL]

how about giving some constructive input to what they should do?

I'd go to my boss and tell him he's hiring incapable personnel which sooner or later will end for the worse of the company.

Something tells me below may apply here

 

[david339933]

SOL71, you keep referring to a material curve in Sec. II.....what curve is this?

 

[Geoff13]

Just a guess, but if you look at the heading for the first column of allowable stresses in Sect II Part D it says "-20°F to 100°F" for USC and "-30°C to 40°C" for metric. The lower temps match the min temps listed by the OP.

I've often wondered why ASME continues to list these lower bounds. They seem like limits leftover from times before UCS-66.

 

[SnTMan]

Huh, possible. Part UCS-23, Maximum Allowable Stress Values, under which the subject material falls, states the allowables for temperature below -20F shall not exceed those for 100F, to paraphrase. So, under Sec VIII, Div 1, there's your coverage.

I don't thing there is anything wrong, per se, with using Code allowables for classes of work that do not fall under a particular Code. If that is what the OPs' organization is doing.

Regards,

Mike



The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

ASME BPVC.II.D.C-2017
NOTES TO TABLE 1A
GENERAL NOTES

(e) Stress values for 100°F are applicable for colder temperatures when the toughness requirements of Section III, VIII, or XII are met.

Regards
r6155

 

[david339933]

Makes sense.....As Mike stated in his first response...20ksi.