Handrail manufacturers often weld straight pipes to elbow connectors, then must grind the welds smooth. To speed this task, some use contraptions like this MB 650 RV product by German power tool manufacturer GeBrax, which attaches to an angle grinder to turn it into a flexible strip sander:
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Other German companies, like Flex Tools and Fein, make dedicated pipe sanders:
There are also a host of sketchy-looking “As Seen on TV”-type companies flogging their own angle grinder attachments…
…but I think I’d stick with the reputable German brands.