UG-84(h)(2)(c)

[Fizza453]

We welded PQR test coupon using 35 mm thick plate, impact testing is a requirement per Section VIII-1 and qualification standard is Section IX. Now, the qualified range of base metal is 16 to 70 mm.
Now per UG-84(h)(2)(c) required minimum impact energy values shall be taken against 70 mm instead of 35 mm from Fig-UG-84.1, is it correct?



Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[weldtek]

You did not specify the type and grade of material tested however, assuming P1 Gr 1 or Gr 2 the difference in required energy for 70 mm vs 35 mm is minimal. Although no one likes to see CVN test results that show minimum passing results, it happens. In my opinion, to properly qualify the procedure it must meet the CVN values required for the actual thickness tested, not the values applicable to the extended thickness that is qualified.

 

[metengr]

There is more to this than simply looking at thickness for CVN test results. Figure UG-84.1 in Section VIII, Div 1 is provided to demonstrate the effects of plane strain behavior (constraint) on material notch toughness behavior. As the strength of the material increases, conditions for which notch toughness change are significant and this is the reason why there are thickness limitations associated with certain material strength values as a group. In some cases, depending on strength of the material, it may show little constraint effect (plane strain) in the presence of notch because the yield strength of the material allows local yielding. The problem is when high strength material is used and is of sufficient thickness where the material will not yield at the notch. Here the fracture strength may exceed the yield strength and result in brittle fracture.

 

[Fizza453]

weldtek,

I do not agree with you regarding impact energy value of weld metal and HAZ specimens.
UG-84(h)(2)(c) reads out the test plate material "shall meet the minimum notch toughness requirements of UG-84(c)(4) for the thickest material of the range of the base metal qualified by the procedure"
Now, UG-84(g)(5) reads out weld metal and HAZ "impact values shall be at least as high as those required for the base materials"

Again my question is, if PQR test coupon thickness is 35 mm and qualified range is 16-70 mm. Now, weld metal and HAZ impact values shall be at least as high as required for 70 mm thick plate (from Fig 84.1) although coupon was made on 35 mm.

Please comment.



Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[metengr]

Fizza453;
Yes, because the thicker material will require higher CVN values to qualify per the Figure, per my previous explanation.

 

[weldtek]

Agreed. Thanks to both of you for pointing that out.