Ouch!!! Double ouch!!!
The code referenced is AWS D1.1. If one is using the 2010 edition, look at figure 4.12. The dimension for "W" is 1 1/2 inches for plate and pipe larger than 4 inches per the table just below the sketch. W is 1 inch if the pipe coupon is equal to or less than 4 inches in diameter.
Best regards - Al