Tensile test failure 1

[weldgal]

Looking at a test report on a SA387 gr. 22 cl 2 weld coupon that passed the side bend tests, but failed both tensile tests in the base metal by 10% (ASME QW-153.1(d) only allows 5% below min tensile). Before testing, coupon was normalized @ 1650 deg F for 2 hours, tempered @ 1250 deg F for 2 hours. Have never seen this kind of failure before, and would like any thoughts on what could have caused this.

 

[metengr]

weldgal;
What is the plate thickness? Also, do you have a MTR on the plate material (chemistry)?

 

[weldgal]

Coupon thickness is 1 1/2". We have MTRs from the supplier.

 

[metengr]

weldgal;
On occasion, having qualified various welding procedures on Cr-Mo plates I have seen where the normalization heat treatment did not result in a ferrite/pearlite/bainite microstructure to meet A 387 Grade 22 mechanical property requirements. The cooling rate for plates greater than 1.25" thickness, during normalizing, is absolutely critical to achieve the desired microstructure (minimum level of retained bainite) that will provide sufficient margin to meet minimum strength requirements after tempering.

In your situation without knowing the specific chemical composition and subsequent carbon equivalent of the plate material, I would suspect the cooling rate after the 1650 deg F austenitization was too low.

 

[weldgal]

According to the lab's report, they used a rise and fall rate of 300 deg F per hour above 600 deg F.

 

[metengr]

weldgal;
This appears to be the problem. The rapid cooling rate necessary for a normalization heat treatment does not follow typical ramp up or cool down rates specified by the Code (like ASME B&PV Code) for PWHT. The cooling rate for a proper normalization heat treatment is optimized based on plate thickness and size to assure uniform thru thickness rapid cooling. The plate should have been cooled at a high rate after removing it from the furnace at 1650 deg F.