ASME II D: different lines for the same material 4

[FPPE]

Hi,

I would manually find the allowable stresses for tubes SB 111-C70600-O61 material because our calculation software (I'm designing an heat exchanger with ASME VIII-1) says that at 316°C the material has not allowable value os stress available.
But, searching for the value in II-D, in Table 1B (pag. 204) there are 4 different lines (from 13 to 16) for the same material (all product form as Smls. cond. tube). Now, in the next page only materials at lines 15-16 are applicable for VIII-1, with max temp equal to 316°C.

Could you explain to me these facts?

Thank you

 

[SnTMan]

The different Codes (and the committees) have different criteria for acceptance of a given material based on the nature of the work and as you can see, often different allowables.

Regards

Mike


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

 

[Krausen]

At higher temperatures for a low-melting point materials you’re dealing with (brass), you will find the never-ending debates on creep properties from various committees/code groups. This is a never-ending issue with continuous ongoing study for some materials. I think the modern version of VIII-1 caps your design temp out at 350F for most SB111 brass tubes, due to their understanding of its creep properties. Note that most brass tubes in cooling service will operate at much lower temps than the shellside design temperature, which can be proven through an HTRI analysis, or similar. So you can look into lowering your tube design temp this way if the code is capping you out

Tolerance is the virtue of the man without convictions -GK Chesterton

 

[FPPE]

I noticed that for brass tubes, Young's modulus are tabulated only up to 200°C in Table TM-3; does this mean that even if the allowable stress values are tabulated up to higher values they still cannot be used in the calculation above 200°C? A warning message appears in the software regarding precisely the absence of Young's module at a higher temperature and the calculation stops.

 

[SnTMan]

Interesting. My 2017 Table TM-3 lists every entry including C70600 up to 700 F / 371 C. Has it been de-rated?

Regards,

Mike



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

 

[Krausen]

I’ll check the current tables here soon, but yes your Youngs Modulus is gone at the higher temp since it no longer applies, as you’ve lost the elastic relationship between stress vs strain due to being in the creep regime for the material. ASME II & VIII-1 will refer to material properties in the creep regime as “time-dependent properties”. VIII-1 does not permit designing in the creep regime in general. ASME II will list some of the creep properties though, showing you where the break point is between elastic vs creep design

Tolerance is the virtue of the man without convictions -GK Chesterton

 

[GD2]

FPPE,
You have to also go through the 'Notes' for the line item, if there is any. In many cases, the Code allows to use higher temperature based on engineering evaluation.

GDD
Canada

 

[SnTMan]

Again, 2017 Ed, SB-111 C70600, Table 1B, time dependent properties at 500 F up to 600 F (max) for VIII - 1.

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

 

[FPPE]

Thank you for the answers!

GD2, I read all the notes and they refer, as Krausen said, to the fact that from a given temperature the values are obtained from time-dependent properties.
SnTMan, in ed. 2021 this table has been updated, certainly considering the fact that these materials have very low yield values, as the recalled notes point out.

Either way, creep for these materials is tabulated from 250/260°C, so there is a 50°C "hole" between the end of the tabulated Young's modulus and the beginning of creep.

 

[SnTMan]

It doesn't make sense to me that modulus at those higher temperatures be withdrawn. Sorry I don't have access to the current Truth

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

 

[FPPE]

SnTMan; I agree with you.

 

[SnTMan]

Maybe a Commitee member will happen by and shed some light

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