well it depends on the pressure in your pipeline and maybe fluid density, for natural gas:
V_((mcf))=(D_((in))^2 * P_((psig))* L_((feet))*0.372) / 10^6
Brad,
In my experience the best way is setting a semi-ancor at tie-in point with a reasonable gap, such as 3mm. Then loads in Tie-in point should be summed (your loads + the other side loads).
And in the case that the other side is not done yet, we estimate the unknown load of the other side...
