Yield Strength Not Coherent

[Engdoitbetter]

Hi engineers,

I was looking for yield strength of SA 537 Cl.1 and I found out that in table 5A of ASME VIII Div.2 (2010) it states 315 MPa while in table Y1 (same standard) it states 345 MPa. Ultimate tensile strength is the same in the two tables.

Do you know the reason for this difference?

Regards,

Stefano

 

[1gibson]

Plate ASTM's can have different strengths for different ranges of thickness. Don't have access to SA 537, but check into that.

 

[TGS4]

1gibson hits the nail on the head. Which thickness are you looking at?

 

[Engdoitbetter]

Dear colleagues,

That's true but the discrepancy is found, in this case, for SA 537 Cl.1 plate thickness less than 64 mm. I was looking for it since I had to design shell plates for the first time and I was a little puzzled by the value of Sy (yield strength) to be used for the hydrostatic load case. Because of preceding calculations I was pretty sure that final thickness would not have been more than 30 mm.
The standard states that in case of pure membrane stress and hydrostatic loading, the allowable stress to be employed in the thickness calculation is 0.95*Sy, i.e. you can stress the material till it reaches 95% of yield stress, whose value, according to the standard, is to be found in table Y1 where it is plotted against temperature.

Table 5A is very clear to me since it reports UTS, Min. Yield and allowable@Temp (which includes safety factor).
Table Y1 is not: it reports UTS, Min Yield (which may be different from table 5A's) and Yield@temp. AFAIK Yield@Temp. is not the same as min. yield, so it is not surprising to find out that Yield@roomtemp is not equal to min. yield, though very close to it.
The strange thing is that min. yield is different, which I cannot understand since usually tensile test are performed at the same temperatures.

Any clues/suggestions?

Regards,

Stefano

 

[marty007]

Stefano,

Heh, something does seem off there.

If you look in the ASME IID-C tables, they match at 50ksi. This would match the 345MPa value.

Anyone else see things differently?

Cheers,
Marty

 

[Engdoitbetter]

dear marty007,

I can't find C tables

 

[PeterSl]

Stefano
Section II Part D 2011 tables 5a and Y-1 agree with a minimum yield strength of 310MPa.

Regards
Pete

 

[marty007]

Engdoitbetter - I was referring to ASME IID - Customary (in-lb units)

PeterSI - I think you're referring to the thickness greater than 64mm


Tables 5a and Y-1 in the customary tables match with a value of 50ksi with matches the higher value of 345MPa.

I'm not saying that's correct either, but it's one more comparison point.

Cheers,
Marty

 

[Engdoitbetter]

Hi,

So marty I think we're dealing with a typo here?

Anyway, my engineering common sense told me I had to use the lowest value (315 MPa) in my calculations.
Do you suggest any alternative approach?

Regards,

Stefano

 

[PeterSl]

Marty, you're right I mis-read the table, had a closer look now and I see the issue.

Stefano, Having had a quick look at a few suppliers and they're all quoting a minimum yield of 345 MPa (or 50ksi). Common practice here is to write your own material specifications that generally copy the standard ones but may have tighter controls on hardness, through section properties or other values, you could the specify 345 MPa and safely use it for your design.

Pete

 

[Engdoitbetter]

Ok, thanks to all for your precious help.

Regards,

Stefano