Technical Bolting | What are the Easiest Ways to Improve Flange Management?

So the first thing is to really work with a bolting flange management contractor to really define a really solid integrated bolting specification. So once you have that in place, now you’ve got to look at what you’re going to do for inspection. So what are the kinds of things that you need for flange inspection? Well you need to look at how you’re going to inspect flanges for scratches and imperfections. Now there is ASME code that helps guide you on this and there’s also the post construction code that gives you some guidance. But you should have criteria in your specification of exactly what are permissible imperfections for scratches and deviations. Whether they’re radial across the gasket face or not and the length and the depth of those scratches. So you need to train your people or you need to have a contractor who’s managing your bolting who understands how to inspect flanges for imperfections.

If you’ve got heat exchangers, then you need to set the specifications for the flatness requirements for heat exchangers. And this is critical, heat exchangers are prone to thermal cycling, they are prone to having different temperature gradients at different parts in the phases of that heat exchanger. So certain parts of the bolted flange are going to be warmer and cooler than others and that can cause for load loss in your bolting. You’ve got to come up with a plan for how you’re going to deal with those. From a flange flatness standpoint, you need to decide how flat your flanges need to be on heat exchangers and what the tolerance is going to be. Because if you simply say within 20 thou flatness, is that plus 20, is that minus 20, is it plus or minus 10? Having that spelled out is really, really key.

And then the question is, how am I going to inspect those flanges on heat exchangers to really eliminate flange flatness issues? And this is where there’s a real big problem because the traditional method of using dial gauges limits how much of that work you can do. So if you take apart 50 heat exchangers on your turnaround between channel and shell and tube sheet, that could be 200 or 250 gasketed surfaces that you need to check for flatness and that is probably just impractical using the schedule that you have in your turnaround and the time it takes to dial in heat exchangers.

So what I advise is you come up with a laser flatness method so you can inspect all that for less money than if you were using dial gauges and having machinist dial flanges in. It’s a way more cost effective way to actually execute the work and instead of doing sampling on just the most critical ones that you think are a problem, you inspect them all. It’s really been found to be tremendously valuable for our clients who’ve done that. And the interesting thing that is sort of an indirect cost benefit for laser flange flatness is it eliminates a lot of logistical issues because you don’t need to move those bundles and components away from the work face. You can shoot them right there and there and only move and transport and pay for transportation of the components that need to be well built up, that need to be machined and really eliminate. We had one client who outside of eliminating leaks and being able to inspect all of these components, they told us they saved $250,000 on one turnaround when we inspected 300 components for them just in logistical savings.