When using Superlok Tube Fittings always select Stainless Steel tubing which is high quality (such as 304, 316, 316L and so on), fully annealed and seamless or welded, ASTM A269, A213 or equivalent. 
Allowable stress value between -20 and 100 (-28.9 ~ 37.8 ) is 19,500 psi
Safety factor is 4 (Ultimate tensile strength is 75,000 psi)
The above data is based on the minimum wall thickness and the maximum O. D. allowed by and under the standard of ASTM A269.