CS vs LTCS Piping on piping class 2500#

[Weko]

Hi all,

I am looking at a Petronas/Shell std for piping class 1500# and 2500#.

On small bore pipe, they specify ASTM A106 gradeB. (normal CS pipe, pipe thickness bellow 20 mm)

While for large bore pipe, they specify ASTM A333 grade 6 (Low Temp CS pipe, pipe thickness over 20 mm).

I am wondering why they specify that? Is it because of the PWHT requirements?

 

[SJones]

It is probably driven by wall thickness and fracture considerations. Shell take a more conservative view than B31.3 with respect to the temperatures and thicknesses that require Charpy testing.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[blacksmith37]

A footnote to SJones good reply; It likely saves paperwork/money to order A333/334 instead of ordering Charpy tests for A106, esp for smaller orders (to get enhanced toughness).
And Shell does better engineering than the great majority of corps.

 

[Weko]

Hi all, thanks for the reply.

I took a look at ASME B31.3, Chapter Material, "Fig. 323.2.2A Minimum Temperatures Without Impact Testing for Carbon Steel Materials".

When a material is thicker, it goes more britle?

Since my current understanding for impact test, is to know the "Ductile-Britle Transtition Temperature".

 

[metengr]

Weko;
When a material becomes thicker you have what is called plane strain condition or a tri-axial state of stress at a notch, defect or crack tip. This condition results in brittle fracture behavior. So, the thicker the material in the presence of a notch, or crack or defect the impact energy is lowered.