A193 B7 studs with A194 L7 nuts 2

[Hani_]

Hello,

Typically in piping specification we see A193 B7 / B7M studs matched with A194 2H / 2HM nuts. However in one particular project client has used A193 B7/B7M along with A194 L7 / L7M nuts.

I have dug into project specifications and documents but could not find a reasoning for this combination of bolts and nuts. I did check the ASTM standard to see the difference in material compositions and noticed that B7 is a closer match to L7 than 2H.

So my question, Is there a particular reason we see B7 studs matched with 2H nuts when L7 composition seems to be more compatible with B7? and if B7 is better matched with 2H would there be an application where we would prefer using B7 with L7 (Like temp conditions maybe?)

Appreciate any insight I can get on this, thanks.

 

[SnTMan]

Hani_, I see no obvious reason to use impact tested nuts with non-impact tested studs. As you say, composition is identical between A-193 B7/7M and A-194 L7/L7M, but proof load, proof stress and hardness are the same for comparable nuts, impact tested or not.

If the Code of construction and project docs give no clue, and the specifying engineer is not available, the reason likely will never be known. Maybe nothing more than availibility.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Rogue909]

There are a couple of reasons. A lot will depend on your project. Few obvious reasons are listed below.

The L in L7/L7M represents that impact testing has been performed. If you don't need the testing (per code, design, etc.) than it is not a requirement.
Supply chain reason---
Often a vendor will supply L7/L7M over 7/7M simply for stock availability. Why maintain an inventory of 7/7M product that is only applicable to a subset of grade 7 users when L7/L7M can be used for all grade 7 users?

As for why grade 7/7M in lieu of 2H/2HM?
Supply Chain Reason---
7/7M is more expensive but tends to cover a broader range of requirements. Usually 7/7M substitution is acceptable; so a vendor may default to providing 7/7M in lieu of 2H/2HM for inventory purposes.

Material characteristics reason---
2H material (1045) does not always effectively through harden during quenching. This results in uneven or un-attainable material characteristics. As your diameters get large (What diameter are you using?) grade 7 (4140, typically) becomes the go to. You can look in to the CCT (continuous cooling transformation) curves in 1045 vs 4140 for a bit more detail.

 

[Hani_]

Thanks guys for your responses.

Actually there is a mistake on my post, the nuts being specified is A194 7 / 7M so no impact testing is required.

The biggest bolt dia we are using is 1". The spec doesn't seem to differentiate change in nut based on size, they are using the 7M nut across all sizes and ratings. However thanks for the insight, I will review the CCT curves for my information.

Most likely as you have noted is that it is based on supply chain reason.For our scope we are going with Standard A193 B7M with A194 2HM for our project purposes.

Thanks

 

[XL83NL]

Great repsponse Rogue

 

[XL83NL]

I can concur with rogue his observations. For a question I had regarding availability and standardisation of studs and nuts, our supplier confirmed they stock more on A194-7 nuts than A194-2H because they have more demand for that grade, since some of their ‘bigger’ customers standardise on grade 7 nuts.