A105 Valves in Low Temp Service - CSA Z662 1

[jskernahan]

All,

I need some help with a CSA Z662 interpretation. Here's the situation:
- I have a CSA piping spec that calls for the use of A105 valves in a LVP (oil), low temp (-45 deg C), PN100 (9930 kPag) service.
- CSA Z662 table 5.1 states that LVP service is categorized at Cat. 1 with no min temp limitation, meaning materials do not need impact testing. Table 5.3 further states that B16.34 valves, any grade, can be used in Cat. 1 without limitation. This is the spec owner's justification behind using A105 material.

I've always said that A105 material is only acceptable at low temps if it has been impact testing (at the low temp), due to the materials tendency to become brittle. Has anyone justified using A105 at -45 deg C without impact testing? And if so what was the reasoning? Thanks,

 

[TGS4]

Considering the current issues with toughness of A105, I would consider its use at temperatures below +10°C ought to assume that the material is brittle/has nil-ductility. I would never take it down to -45°C at any reasonable stress level.

 

[David2007]

Hi,
It depends on the thickness and the fluid category as it shows on the Fig.323.2.2A page 48 ASME B31.3 , if it its Category D Min.-48 is allowed without impact test for wall thickness less than 10mm.

 

[weldstan]

You hould assume that the A-105 will have yield stess = to tensile stress at -45 C. In short it will be brittle with less than 5 ft-lbs absorbed energy in a Charpy V-notch test. It may still be usd if the applied stress is much lower than the MSYS in service and also if you intend to pressure test (similarly low applied stree) at a low temp.

 

[GD2]

jskernahan,

I have come across few pipeline spec where they prescribe A105 material for the service condition you stated. I am assuming you are talking about station piping spec for pipeline to CSA Z662 code.

CSA Z662 is one code that allows B16.34 to be used to all min temp which to the code is -70C.
I had looked into this in the past myself to find the logic. I have derived couple of logics to support this.

Codes considers modern mills produces better product with better grain refinement. Example, are the higher stress values that can be seen in ASME BPVC Sec II and B31.3 etc. in different editions.

Another aspect of CSA Z662 is that CSA design is based on fracture mechanics.

If I was to write the piping spec, I would have specified A350LF2 valves for low temp service upto -50C. Now, if you look at A105 and A350LF2, they are like half-brothers. their Strengths are the same, chemistry almost similar and placed under the same material group 1.1 for temp-press ratings. The major difference is the manufaturing process. A350LF2 goes through a heat-treatment process for grain refining whereas A105 do not.

A105 is usually used for flanges,fittings and valves limited to smaller sizes. For larger valves, it will be A350 LF2, A352 LCC or A216.

Smaller sizes of pipes and fittings including valves poses a lesser risk of failure as the nominal/hoop stress is also proportional to the diameter. The larger the dia, the more the hoop stress. for example, for a design pressure of 9930 kpag, a 2" x 5.54 mm WT (XS) pipe will be only opearting at only 22.4% of SMYS whereas a NPS 24 x 12.7 mm WT (XS), will be operating at 61.8% of SMYS.

My guess is that put all these factors together, CSA Z662 allows A105 material to be used to its minimum design temp without impact testing.

By the way, what is the size or size range A105 valves are specified in the piping spec.? Most likely, it will have limitaion to the size.




Ganga D. Deka, P. Eng
Canada

 

[GD2]

jskernanhan,
To add, ASME Sec Div 1 UCS-66(b) allows a further reduction of MDMT of carbon steel materials based on the stress ratio (Fig. UCS-66.1). B31.3 has taken the same curve from ASME BPVC (the mother of all ASME piping codes) and added to it's code. For example, if the stress ratio is 0.7, it gives a further reduction of 22C to -29C. The reduction is limited to -46C only. This explains why a standard material like A105 can be used up to -45 MDMT without impact testing. At the end of the day, it is all about the stress in the pipe.

A quick calculation will show that A105 material up to NPS 24 can be used up -45C MDMT for 9930 kPa MOP.

Ganga D. Deka, P. Eng
Canada

 

[weldstan]

GD2,
ASME B31.3 produced these curves well before ASME VIII, Div.1.

 

[jskernahan]

Thanks GD2, they are small bore valves so I suspect you're right about the hoop stress justification.