There has been a substantial amount of improvements over the years in flange leakage prevention. But is it enough? The improvements have been mostly mechanical, bolting two flanges together by forcing them in place. This methodology has its drawbacks: It can introduce unwanted stresses, poor gasket compression, deformed sealing surfaces and much more.
What if we could look at flanges from a 3-D perspective and apply proper geometric controls such as parallelism, true position and relationships to mating flanges? What is the long-term benefit of getting two mating flanges in the optimum condition before bolting?
When field machining companies are contracted during turnarounds, they bring a range of flange facing machines on-site. They sit in the yard until they are ready to be used. When needed, the flange facers are typically ID mounted to sweep a dial indicator to determine if the flange needs to be machined. Sometimes it can take an entire shift just to get the machine in place. Once in place, the machine runs in one path around the flange with a dial indicator on the end of it. The machinist visually monitors the deviation and writes down the observed highs and lows of the surface in question. When the deviation exceeds the engineering tolerances, the flange is then machined. This has been the process for many years.
There are major problems with this process. It never takes into consideration the angularity changes of the flange post-machining. The effect of a flange that changes angle by just a half degree over 20 feet on a pipe run is several inches. Now the bolts’ holes do not line up, the sealing surfaces are not parallel to one another, and a mechanical device needs to pull each flange into position for the bolting procedure. This introduces many unnecessary stresses on the piping and the flanged connection.
The indicating process is not repeatable. If two different technicians set up a machine on the same flange, their results will likely be different. Also, the technician needs to record everything by hand on a piece of paper, which adds to the possibility of misinterpreted results. This form of documentation is not traceable and is not easily archived.
Now we step into the 21st century. A trained metrologist certified in geometric dimensioning and tolerancing (GD&T) sets up a portable coordinate measuring machine (CMM) such as a laser tracker or articulating arm. When the flange(s) to be inspected have landed in the yard, the metrology specialist can inspect several large flanges in minutes as opposed to hours. When the flange cannot be relocated outside the unit, the laser crew can easily mount the equipment on the flange and inspect it in place just as quickly. No crane, chain falls or hoists are needed.
Once the portable CMM is in position, the technician scans the flange face, collecting thousands of data points. Once the data is collected, it is run through a custom macro, which displays the results in an easy-to-understand heat map that details the high spots, low spots and everything in between. There is no guessing, and the process is completely repeatable whether one or five different technicians collect the data. The process is completely electronic, traceable, repeatable and highly precise, and the results are easily archived for future reference.
Here are the benefits:
1. The reports are digital documents that can be archived for historical tracking.
2. Repeatability makes it a process based on the most precise equipment possible in the field.
3. Set-up and data collection are fast, and speed matters during a turnaround.
4. The process is safer during the data collection.
5. The flanges are less likely to leak because proper GD&T is used during the machining process to ensure parallelism, position and minimum/maximum distance were applied.
6. Flanges are in the most optimal position possible.
For more information, visit www.dimensional3d.com or call (832) 819-5661.
