We routinely faces Class 2500 CS flanges and back side nut landing areas all time and normally no inspection is carried out other than possible thickness measurements.
On SS flanges of all classes and sizes we PT before and after machining. This required because we have problems with Chloride SSC. We normally don't reface Class 150 flanges. On large SS flanges where we suspect SCC and if there is radial flange crack we will check while machining.
Hi unclesyd
thanks for your reply but I want to clear my question, for flange rating 1500 what is suitable flange facing, raised face (RF)or ring type joint (RTJ),and does selection based on service also ex.hydrogen service,H2S content.
Both type of flanges the Raised Face and the Ring Joint flanges can be refaced. The only thing is that you have to watch out for overlay on some flanges in H2S service. The was a lot discussion about weld buildup and machining of flanges in H2 service, The information I have is if the proper electrode is used there is not problem.
The problem with RTJ Flanges is that they aren't many machines out there and usually the refacing is done by speciality contractors. I've seen several jobs where the people claimed the ability to reface RTJ's Flanges but in the end they failed miserably. We took the approach that it was the last resort to face a RTJ Flange. We have literally thousands of 3/4"-2" RTJ Flanges that get made up at least one and possibly 10 times a year, so we watch these closely as we don't machine on these we replace the flange, it's cheaper. There is a set of gauges for RTJ Flanges that will help you decide the condition of the seating surfaces.
One thing you can do is rent the tools to machine the Raised Face Flanges. This works out depending on the number of flanges and whether you want a contractor to come in.
On the Raised Face Flange, especially in our jacketed polymer piping system we routinely machine them. We have the in house capability of field machining up to 96" OD flanges. As I mentioned above we will back spot face the bolt hole, which is done more often than refacing.
We use spiral wound gaskets on our Class 2500 polymer piping flanges. On any hot vapor we will use an RTJ flange face. We do not reuse the rings.
I mention in my post about using PT while machining shown in this example. A little trick in doing this is to check and clear the and then apply a new coat watch whole machining. When you finish machining PT to clear the flange.
I'm a big fan of the Climaxx Machines and even though I don't have any experience with the new swing arm with a milling head. All of ours were the single bit swinging systems. Interrupted cut were tough whereas now the milling head want even know they are there.
