I have to purchase a line pipe with a material grade L450 ME. I suppose that "M" stay for thermomeccanically rolled condition. But the ulterior suffix "E" for what is?
It stands for pipe ordered to Appendix M for European onshore natural gas transmission. I don't know what the difference is, but I assume this was to incorporate the requirements of the EN line pipe code (EN 10208-1) so that it could be withdrawn, as indeed it now has been.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.