Impact test criteria 3

[svi]

Interpretation 21-28 included with the ASME B31.3 2008 edition says,

"materials, for which a temperature of ?20°F (?29°C) is listed in the Minimum Temperature column of Table A-1, are exempt from impact testing for any combination of thickness and temperature above ?20°F (?29°C)"

Whereas Fig 323.2.2A note 1 says,

"Any carbon steel material may be used to a minimum temperature of ?29°C (?20°F) for Category D Fluid Service."

The interpretation does not say that it is limited to Category D service. Cat D service is limited to 150 psi (g) design pressure and applies to relatively lower thicknesses.

Can someone please clarify the above?

 

[trottiey]

I'm new to piping codes, but stepping through these puzzles to try to learn.

Take a look at Table A-1 minimum temperatures. Some materials have a temperature there, while others have a letter designation. Table A-1 note 6 says that if there's a letter designation, that's when you go to Fig 323.2.2A.

I would conclude that interpretation 21-28 applies to the materials with a single number for minimum temperature, while the figure 323.2.2A note 1 applies to materials with a letter designation.

 

[Duwe6]

svi, you may be overthinking the problem. An 'Interpretation' goes beyond the current Code, or covers something not addressed in that Code. In this case, it looks like the B31.3 Intrepretation has expanded the exemption from -20°F for Cat. 'D' only, to -20°F for *all* categories.

BTW, this now matches Sect VIII Div-1. no Charpys needed for 'normal' materials at -20°F or above.

 

[jamesl]

trottiey is correct. The interpretation applies only to materials that has -20F listed in Minimum Temperature column in Table A-1. There are other carbon steels that require impact testing at -20F.
The note in 323.2.2A states that these these carbon steels will also be exempted from impact test if the pipe is in Category D service.

I don't understand what "normal" material Duwe6 referred to. UG-20(f)of Div1 exempt regular carbon steel from impact testing only up to 1" for -20F and above MDMT.

 

[svi]

jamesl,

The para 300.2 of ASME B31.3 definitions gives,

'Normal fluid service' as a fluid service pertaining to
most piping covered by this Code, i.e., not subject to
the rules for Category D, Category M, or High Pressure
Fluid Service.

The 'normal material' may be one that is suitable for such service.

Duwe6,

Should not the code be clear in the first instance. Normally one only reads the requirement what is contained in the code text. It is only perchance that I came across this.

 

[trottiey]

Guys, please don't make stuff up. The code is already complicated enough without that.

When trying to understand the code, it's generally a good idea to start by reading the core text, not the pictures or the appendices. Read paragraphs 323.2.2 (a) and (b) carefully. They say that if your minimum temperature is a number, then you go to the table, but if it's a letter, then you go to the figure. And if you go to the table, you'll find it's full of exemptions for temperatures above 29C.

Interpretation 21-28 just summarizes a shortcut through that. It is not talking about the category D exemption and does not expand it. Code interpretations never overule the code; it takes a code case, errata or code revision to do that.

 

[svi]

trottiey,

Do you mean 'below'?
in,
"And if you go to the table, you'll find it's full of exemptions for temperatures above 29C"

Agree that Interpretation is a code case. How would you understand the impact test criteria for CS material with the min temp of -20 deg F in Appendix A1? Is it needed to be done for temperatures above that for any thickness?

 

[trottiey]

No I meant above, but I missed a negative sign. It should have read:
"if you go to the table, you'll find it's full of exemptions for temperatures above -29C."

The interpretation is not a code case.

Impact testing is not needed for any CS material with a min temp of -20F (-29C) in Appendix A, so long as the design minimum temperature is equal or higher. This is true regardless of thickness. We can arrive at that conclusion from looking at the table, or by taking the shortcut through the interpretation.

 

[svi]

I am not sure how this conclusion can be drawn from the tabulation. Say A106 Gr B is a material that is to use curve B values. At 20 deg F, it corresponds to 0.5 inches. How is it possible to conclude that impact testing is not needed above the 20 deg F temperature?

 

[trottiey]

Interpretation 21-28 does not apply to A106 Grade B because there is no temperature listed for it in Appendix A Table A-1. Impact testing may be required on A106 Gr. B thicker than 0.5" with a design minimum temperature between -20F and +75F, depending on the exact combination of temperature and thickness.

The key is to read carefully. Take the phone off the hook, take a minute to clear your mind, and concentrate.

SA-106 Grade B has a letter designation in Table A-1. (i.e. curve B.) That means that paragraph 323.2.2(b) applies, and it sends you to Fig. 323.2.2A. That's where you get your minimum temperature from. If this is category D service, then your mimimum temperature is -29C(-20F), thanks to Note 1 of the figure. Otherwise, you look up your thickness, and read off the minimum temperature from the curve.

Once you have your minimum temperature, you take that to Table 323.2.2, line 3. You go to column A or B depending on whether your minimum design temperature is above or below the temperature you just got from the Figure. Cell A-3 boils down to no impact testing required, and Cell B-3 boils down to requiring impact test of everything.

 

[svi]

Is it not that the curves and the tabulated values are the same?

Let me try an ASTM A106 Gr B of 15 mm thickness and a design minimum of -20 deg C. From curve B for the A106 material of 15 mm will correspond to -15 deg C. This being above the -20 deg C, I should see the column A tabulations.

Why is it needed to refer to tabulations A or B depending on the temperature read off from the curves. Don't the curves correspond to different materials listed in Appendix A1. How is it possible to say that impact test is not if curve A is selected from the above.

The note 1 is applicable to the curve A and the tabulations in column A, and applies to Category D service.

 

[stanweld]

svi,
Category D Service is considered so mild and non-safety related that dispensation from the normal impact testing rules of B31.3 has been granted.

 

[svi]

stanweki,

The interpretation is the general understanding and is identical to what is there in Section VIII Div 1. Note 1 referenced above limits it's applicability to category D fluid service. The interpretation does not limit it to category D service.

 

[stanweld]

svi,
Please note that the Interpretation does not apply to A-106, which does not have a minimum Temp of -20F defined in Table A-1. Curve A in Fig. 323.2.2A applies.

 

[svi]

Thank you stanweld. That's it.