Exempt Material Failing Impact Tests 3

[ConstantEffort]

Is the justification for exempting carbon steel materials per Figure UCS-66 because the exempt materials are expected to achieve the results that would be required by Figure UG-84.1?

I accidentally purchased some 3/8" thick SA-516-70 as rolled plate with impact tests to -20°F. This plate is exempt from impact tests under the rules of Section VIII Div 1. The test results failed the UG-84 requirements though!

The supplier's response is that they expect all thicknesses of as rolled SA-516-70 to fail impact tests regardless of thickness. They recommend normalizing everything. My assumption is that ASME expects the material to pass these tests easily and it is not worth testing.

So I ordered up 3 more tests of 3/8" as rolled 516-70. The three tests are from three different heats sourced from two different US mills owned by different, well-known companies.

Mill A failed its only test, at 13, 14, and 15 ft-lbs with an average of 15 ft-lbs required.

Mill B passed both tests, with 15, 18, and 19 ft-lbs on one and 33, 35, 38 ft-lbs on the other.​

All CMTRs claim as rolled condition and everything was within SA-516-70 chemistry limits.

Referencing some concerns on piping and brittle fracture at -20F even though exempted by B31.3 (link), the Mn:C ratio was a concern. One possible solution was to require a Mn:C ratio of 5 or greater. The plate that failed had a Mn:C of 5.4. The two that passed had ratios of 6.1 and 6.2.

So, the original question again...
Is the justification for exempting carbon steel materials per Figure UCS-66 because the exempt materials are expected to achieve the results that would be required by Figure UG-84.1?

 

[JStephen]

There's a little "NOTE" partway down through UCS 66, which says, "Note: The use of provisions in UCS 66 which waive the requirements for impact testing does not provide assurance that all test results for these materials would satisfy the impact energy requirements of UG-84 if tested."

 

[Mech2325]

Jstephen: So, what should we do if we are being exempted from impact test by the rules of UCS 66 or 67. Should we still order an impact test just to check if it passes the requirements of UG 84?? I did not get what this note is actually trying to say

 

[metengr]

What it means is this.. if a material has been exempted from impact testing by virtue of UCS-66 it does not imply the material possesses impact energy values that will meet the energy values in UG-84. In other words, designer beware.

 

[JStephen]

I think the issue is that brittle fracture and notch impact testing are not exactly the same thing, but similar. So passing impact tests gives you some reasonable assurance that you won't have brittle fracture. But failure to pass the impact test doesn't guarantee that you WILL have brittle fracture. So there's material/temperature combinations that are known not to have brittle fracture issues even though they don't always meet the impact tests.

IE, the "exemption" means you don't need to test it, but it doesn't mean that it will automatically pass the test.

 

[weldstan]

The Codes have never been the be all and end all for design. As metengr stated, let the designer beware. When we look at actual brittle fractures in low carbon, low strength steels, the absorbed energy at the failure temp was generally 5 ft-lbs or less.

 

[r6155]

I accidentally purchased some 3/8" thick SA-516-70 as rolled plate with impact tests to -20°F. This plate is exempt from impact tests under the rules of Section VIII Div 1. The test results failed the UG-84 requirements though!


This is a commercial topic
The order is over rules of ASME VIII Div.1, hence the order was not complied
The supplier’s response is out of time. The supplier must to advise, prior to accept the order, that normalizing is required to achieve the required values of charpy test

See SA-20
12.1.1.1 Plates Ordered Without the Heat Treatment Specified
by the Applicable Product Specification—If the applicable
product specification requires heat treatment but the plates are
ordered without such heat treatment and Charpy V-notch tests
are specified, one coupon shall be taken from each plate-asrolled.
The coupon shall be heat treated in accordance with the
applicable product specification and the purchase order and the
plate shall be qualified by test specimens taken from the
heat-treated coupon.

SA-20 requires, for SA 516-70 0,375” , 15 ft-lb min average and 12 ft-lb min one specimen with test temperature at
-50ºF (not -20ºF). Never I purchase different values than those in the rules to prevent discrepancies, and the most important: remaining plates can be used for next works with full conditions with SA-20 (Charpy in this case).

Regards.
r6155