Get away! That is superficial surface rust on the flanges.
More of a concern is that you will have a lot of trouble getting the bolts off and the dangerous bit is the bit you can't see - i.e. the condition of the bolts inside the flange.
What you should do is remove the flange, replace the bolts and grease them well and blast clean the flanges. Then paint them or coat them in something suitable before re-assembly. Power wire brushing might get rid of the rust, but tends to smooth the surface leaving nothing for the paint or coating to grip onto.
You Might get away with changing one bolt at a time but "high critical service" is a vague term without meaning in piping design terminology.
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