Because PVC tank liners are custom fabricated for an exact fit we require precise measurements of the area to be lined. Of those dimensions the most critical would be the inside dimensions of an outlet. Whether too big or too small, an ill-fitting outlet can lead to a premature failure of a flexible liner.
If the inside diameter of the pipe is measured over-size the liner outlet will be made too small to fit inside the outlet. As solution passes through the outlet the liner will expand. Without the support of the rigid pipe the liner will expand to a point where incredible stress will be placed on the weld where the tube of the outlet is attached to the flange face. This can cause the liner outlet to shear off from the liner.
If the inside diameter of the pipe is measured too small the excess material of the liner will not allow the flange face to lay flat on the inside of the tank. This will cause the area where the outlet tube and flange face meet to bunch up and crease. This will cause stress on that weld and could lead to that weld failing.
Like my earlier post on how we size liners, provide us with the accurate and true inside dimensions of the outlet. Leave any size adjustments to us to make and the result will be a perfect fitting outlet.
Outlet that failed due to given pipe dimensions were under-sized