Charpy Impact Values

Why are the Charpy impact values from my test welds lower than that printed on your Certificate of Conformance?

The test results on our Certificate of Conformance were obtained from welding an AWS filler metal test plate. Any change in welding procedure will affect Charpy impact values. Below are common practices for welding test plates when Charpy impact specimens are required:

Controlled heat input
Controlled preheat and interpass temperature
Even number of passes per layer
Build-up cap pass to maximum allowed in specification