Hi,

If you add the field in the sale order form, do the same for product form also, add a field in product master,

And when you select the product in ordelines, you can display the value corresponding to the product from the master. 

Add a field name 'x_u12' in sale order line, make it as related field with the product field.

Thanks

Amin Abi,

Define the new field in product's view and make  the field related field with your sale order form's field x_un12.

Thank you