B7 stud bolts for low temperatures (-45¦C)

[vcmkumar]

I am trying to specify ASTM A193 B7 stud bolts for A105 or A350 LF2 flanges for low temp down to -45ºC.

AS4041 Table G1 allows for the bolts, a min temp of -30ºC with Carbon steel flanges (min yield 240 MPa), but -48ºC with low alloy steel flanges (min yield 724 MPa).

Why is the min. temp of the bolts tied to yield strength of flange material? If B7 can be used to low temp. as -48ºC, why cant they be used with low temp CS flanges like A350 LF2.

Also if my alternative is to go for A320 B4 bolts instead, what is the justification?

 

[metengr]

From the perspective of ASME B31.3, ASTM A 193 Grade B7 bolting material is suitable down to -40 deg C (-40 deg F) with no impact testing. Now, if you went with ASTM A 193 Grade B7M, this would provide a minimum metal temperature of -48 deg C (-55 deg F) with no impact testing.

If you are looking to use Grade B7 material below -40 deg C, this would require impact testing for use. However, it might be more conducive to go with A 320 B4 bolts only because they are suitable for low temperature service conditions.

 

[vcmkumar]

Thanks metengr,

Concern is some standards specific to flange bolting like AS2528 or DS-EN-1515-1 give the lower limit as -30ºC or even higher.

Why the discrepency between standards?

Also, if you note the following from ASME B16.5:

"2.5.3 Low Temperature. Some of the materials listed
in Tables 1A and 1B, notably some carbon steels, may
undergo a decrease in ductility when used at low temperatures to such an extent as to be unable to safely
resist shock loading, sudden changes of stress, or high
stress concentration. Some codes or regulations may
require impact testing for applications even where temperatures are higher than ?29°C (?20°F)."

The application I'm looking at is for a gas pipeline station piping where cold temp excursions may occur during depressurisation / re-pressurisation. Transient modelling shows that Gas temperatures could go down suddenly to -45ºC or so. We would therefore expect the bolts to be exposed to such temperatures (theoritically).

Your comments please.

Cheers
Manoj

 

[SJones]

If you are that worried, what's wrong with A320 L7?

Steve Jones
Materials & Corrosion Engineer

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

 

[gr2vessels]

Manoj,
Various national standards include specific local issues in the context of limitations imposed for the use of materials in the pressurized systems. For instant, if the temperature of those bolts will drop from + 40 C (piping in Australia) to - 45 C, the same bolts will behave differently in North Alaska (drop from -5 C to -45 C). I would not waste any more time dwelling on 'why', when the applicable codes are clear on what is the minimum operating temperature the bolts can be used without additional impact test. You still can use this type of bolting at lower temperature, but those bolts have to be impact tested by the manufacturer to prove you the suitability at lower temperature.
However, if you want to be very detailed in analysis, you might be better off in calculating precisely the pipe actual temperature at depressurization and calculate the actual temperature the bolts could really see. The bolts and the flange OD would never see any near the mentioned -45 C, because the heat transfer to the environment during the sudden, but short lived depressurization.
Cheers,
gr2vessels

 

[TVP]

As SJones mentioned, ASTM A 320 Grade L7 bolts are intended for low temperature service: these fasteners are rated to - 101 C. The composition and properties are essentially identical to ASTM A 193 Grade B7.

 

[NDGuy]

If one had to perform impact testing, what is the impact test reference (I know it is colloquially called Charpy v-notch) and what is the mimimum impact energy? Thanks in advance.

 

[gr2vessels]

NDGuy,
SA 320, Clause 6.2 gives extensive details...
For SA 193, the supplementary S2 says:
.."S2. Charpy Impact Tests
S2.1 Charpy impact tests based on the requirements of
Specification A 320/A 320M, Section 6 and 7 shall be
made as agreed between the manufacturer and the purchaser.
When testing temperatures are as low as those
specified in Specification A 320/A 320M, bolting should
be ordered to that specification in preference to this specification."
Howzat?
Cheers,
gr2vessels

 

[TVP]

NDGuy,

As gr2vessels pointed out, ASTM A 320 defines the requirements for energy (depends on alloy) and testing (ASTM A 370). If your company specifies fasteners according to ASTM standards then you really should have both of these standards.

 

[metengr]

NDGuy;

.....and what is the mimimum impact energy? Thanks in advance.

The minimum impact energy should be specified by either the code of construction, process requirements or by the design engineer.

 

[NDGuy]

Thanks for the very helpful feedback!

 

[unclesyd]

Make sure that if you require impact testing on any fastener remember that when it is shipped to a distributor the fastener is usually commingled with others of the same size whether impact tested or not.
It takes a little effort to get any quanity of the same lot of fasteners unless you are dealing with the factory or ordering with a longer delivery period.