Requirement of Charpy Test for A106 Gr. B as per B31.8

[anapaz79]

ASME B31.3 claims that no Charpy Test is required for A106 Gr. B if the design temperature is equal or above -29ºC, and I have doubts if this can also apply to ASME B31.8, since it does not specify.

For your information these pipes shall be used for compression gas station in Mexico (design factor 0.5), the DN un 3" or below.

I would really appreciate if someone could give me any info or opinion.

 

[XL83NL]

Im unfamiliar with B31.8, but have been using B31.3 for a short while now; I would look up the same approach for B31.8 as for B31.3, as the code have the same organization.
From a quick scan, I believe para 812 of B31.8 addresses your answer;

Some of the materials conforming to specifications
referenced for use under this Code may not have properties
suitable for operation at low temperatures. Users of
this Code are cautioned to consider the effects of low
temperature and the potential impact on fracture performance
at low temperatures.
Whenever the minimum design temperature is below
−20°F (−29°C), a fracture control program shall be established.
The program shall address parent materials, the
parent material seam weld (if present), circumferential
buttwelds, attachmentwelds and anyweld heat affected
zone (HAZ).

 

[anapaz79]

Thanks XL83NL,
I had already read this point, the problem is that this is adressed to welds but it does not mention the Charpy on the material itself. This is my main concern.

Regards

 

[metengr]

I checked B31.8, here is some background information


Review 841

841.1 Steel Piping Systems Design Requirements

(1) Brittle Fracture Control
To ensure that the pipe
has adequate ductility, fracture toughness testing shall
be performed in accordance with the testing procedures
of supplementary requirements SR5 or SR6 of API 5L,
or other equivalent alternatives. If the operating temperature
is below 50°F, an appropriate lower test temperature
shall be used. The appropriate lower test temperature
shall be taken to be at or below the lowest expected
metal temperature during pressure testing (if with air or
gas) and during service, having regard to past recorded
temperature data and possible effects of lower air and
ground temperatures. The average shear value of the
fracture appearance of three Charpy specimens from
each heat shall not be less than 60%, and the all-heat
average for each order per diameter, size, and grade
shall not be less than 80%. Alternatively, when dropweight
tear testing is specified, at least 80% of the heats
shall exhibit a fracture appearance shear area of 40% or
more at the specified test temperature.

The above applies to base material. I am not going to extract any more excerpts - you can review the material yourself. It is self explanatory.

 

[weldstan]

Assuming that the pipe in question is 3" diameter and below as indicated in your query, and the gas will heat up during compression, why are you concerned with brittle fracture? While B31.8 mandates 50% of SMYS maximum design, you cannot buy pipe thin enough to approach the design requirement for 1500 psi and under systems.