Oil & Gas Innovation Summer 2020 Digital | Page 15

As a spacer coupling allows for two points of flexure, tolerances (measurements) are expressed as two angles. Picture 3 (right) shows the horizontal alignment, and picture 4 (right middle) shows the vertical. The current setup runs at 3575 rpm. This is important why? The speed of the rotation sets the tolerances for the alignment. At 3575 rpm and spacer coupling the tolerances for shaft alignment are: Picture 3 ANSI/ASA S2.75-2017 (spacer coupling type) Offset Angle N/A 1 mil/ft (0.06 mm/m) Table 1. Shaft alignment tolerance as per ANSI/ ASA S2.75-2017 Both horizontal and vertical angles are well within tolerance (thus the green colour in the result pictures). However, remember that we left coupling and pipe flanges unbolted? The true test of an installation (besides starting it up off course) will be in bolting up the pipe flanges. This should be done under strict supervision (measurement) and should be documented and handed over to the asset owner as proof of a job well done afterwards. In this case (picture below) the crew left the laser shaft alignment system mounted on the coupling as they proceeded to torque the bolts. The alignment system has a feature to monitor movement and graph it, in horizontal and vertical direction, as the flange bolts are being tightened. This allows the crew to determine if there is any pipe strain affecting the pump, ultimately adding stress to the machines. As you can see in the picture with the graph there is quite a lot of movement both vertically and horizontally with 7.1 mils (1.8 mm) in vertical offset and 19.5 mils (4.9mm) in horizontal offset. Going back to the ANSI/ASA S2.75-2017 standard: “External forces from piping strain, flange strain, conduit strain, attached ductwork, etc., applied to machine cases shall not be sufficient to cause changes in the shaft alignment of magnitude greater than 50 micrometers (2 mils) vertical or horizontal measured at the coupling.” If the crew would have proceeded with final alignment under these circumstances, they would have seen all kinds of issues, likely manifesting themselves as soft foot. However, this is not a condition you could have fixed using the soft foot playbook (step shims etc). The pipe stress would have been there, adding distortion to your pump case, possibly shaft deflection, causing vibration and ultimately you would see bearing damage because of this. If you want to make sure your assets run for their entire designed life span, you make sure to take out pipe strain before proceeding to final precision alignment during the installation process. • If you would like to know more about the solutions discussed in this article please contact: Easy-Laser AB T: [phone] W: www.easylaser.com E: [email protected] Picture 4 Tightening flange bolts as the laser shaft alignment system measures any shaft deflection. Graph illustrating movement both vertically and horizontally as the pipe flange bolts are tightened.