ASME Section VIII Division 1 is updated by ASME with Addendum 2009b. This version is valid on 1st of June 2009. I updated my codes also and I noticed the big change on Item UG-115(b) of ASME Section VIII Division 1.

It is stated in Item UG-115(b) of ASME Section VIII Division 1 that "The units of measurement used in Manufacturer`s Data Reports, Manufacturer`s Certificates of Compliance (UG-120), and capacity certification of pressure relief devices, and in marking or stamping pressure vessels, pressure vessels parts, and pressure relief devices, required by this Division, shall be either U.S. Customary units or SI units." Until this senteces, everthing is clear. But...

"However, one system shall be used consistently throughout for construction of pressure vessels. This includes all phases of construction (e.g., materials, design calculations, reports, fabrication, marking and stamping. See U-4."

If an AI read this sentence, he asks you that "although you use SI units, you must indicate all ASME flanges, ASME pipes and fittings etc. in SI units too". It is ridiculous, but the UG-115(b) says that.

In Addendum 2009b of ASME Section VIII Division 1, this last sentence which begins "however", was removed. Therefore, you can use dual unit system. Nobody care it anymore.