CSA Z662 Category I pipe be substituted for Cat. II pipe?

[CALGARY007]

Hi,
I am writing our company CSA coded piping spec., and I have a question for the material substitution.
As per CSA Z662-11 Table 5.1,Cat. I pipe may be substituted for Cat. II pipe in pipe runs shorter than 50m. So if for a low temp(-45 C)piping spec, A106B & A333Gr.6 are Cat. I pipe, and it can be substituted for CSA Cat.II pipe in pipe runs shorter than 50m? But as per ASME B31.3 Fig.323.2.2A, minimum temperature without impact testing for A106B is -29C.
So can I put A106B & A333 as the substitutive pipe for CSA Cat.II pipe or just A333 at the CSA coded low temp piping specs.
Btw, A106B is for normal temp and A333 is for low temp at my company ASME coded piping specs.
Thanks,
Carl

 

[SNORGY]

The ASME Codes and the CSA Z662 Code differ in the kind of fracture that is of the most concern. Z662 is written around the general idea that longitudinal fracture along the axis of the pipe is the primary concern, whereas ASME B31.3 is less specific about the orientation of the fracture to be concerned about.

Just to clarify what might be a bit of a misunderstanding that you have...

(1) CSA Z245.1 Cat. I = no notch toughness properties need to be proven.
(2) CSA Z245.1 Cat. II = notch toughness properties to be proven by satisfying both absorbed energy on impact (e.g., Charpy) and fracture surface shear area criteria (3 specimen average 60% with no single specimen below 50%).
(3) CSA Z245.1 Cat. III = notch toughness properties to be proven by satisfying absorbed energy on impact (e.g. Charpy) criteria only, with no subsequent analysis of fracture surface for shear area.

A106-B pipe meets Cat. I, whereas A333-6 pipe is generally accepted as meeting Cat. III.

Oddly enough, both Codes have a similar philosophy in terms of determining when impact tested material is required, and when required, how tough it needs to be. Examine ASME B31.3 Figure 323.2.2 (b). The lower is your combined longitudinal (tensile) stress level, the lower an MDMT you can accept without requiring impact test qualification. In CSA Z662 Tables 5.1 and 5.2, the criteria is PTSV (Pipe Threshold Stress Level), and the lower is your hoop stress relative to PTSV, the less stringent your proven notch toughness requirements become. So, in very general terms, the lower the hoop stress, the less fracture toughness is required. (Deferring the discussion about Ductile To Brittle Transition Temperatures for now...).

Some of the pipeline majors, to simplify things, only use Cat. I (A106-B) up to a hoop stress level of 50 MPA, and then apply CSA Z662 Table 5.3 and its footnotes for any further limitations on MDMT. In the specifications that I have been in charge of, I tend to not use A106-B in any CSA Z662 installation where MDMT < -29 C, to avoid the situation you find yourself facing now.

Read the footnotes in Table 5.3 carefully, and also the literal definition of "piping run length" in CSA Z662. You can usually make a Cat. III for Cat. II substitution for 100 m, and a Cat. I for Cat. II substitution for 50 m, unless one or both of the following are true:

(1) CO2 service with a hoop stress above 50 MPa.
(2) Hoop stress in pipe greater than the corresponding upper PTSV limit in Tables 5.1 & 5.2.

In all instances, evaluate the actual piping hoop stress and compare that against the PTSV to determine what notch toughness properties, if any, need to be proven.

 

[CALGARY007]

Very clear answer.
Thanks Snorgy.