Personally, I would use a 0.120" wall thickness for 4130 CrMoly, which is a standard size.... Using Lloyd's tube strength spreadsheet for the 1.375" OD x 0.120" wall at 4500 psi I get safety margins of 2.7:1 to Yield and 4.1:1 to Burst.... ASME require 3.5:1 to failure, but only 1.5:1 to yield (worst case, after maximum possible cycles), but Lloyd and I always use at least 2.5:1 to Yield.... If you want a 3:1 safety margin to Yield, you would need to increase the wall thickness to ~ 0.150", which is not a common size, the next size may be 0.188" wall.... adding weight and losing internal volume, of course....

Please note, I am NOT an Engineer, you are responsible for your own build....

Bob