Please don't do this for vulcanite/ebonite stems. Water this hot will make these materials really pliable and may result in you turning your straight stem bent, or otherwise altering the cant/rake/angle of your stem.
I have no experience with acrylic stems at this temperature, but have to think that there may be similar (if not as considerable) effects.
@abdulaziz - I'd like to address one of your earlier questions, about shank brushes. I think that a shank brush is a pretty important tool to have, especially in the absence of using an alcohol based solvent to dissolve tars, dottle and resins left in your pipe from smoking. For your stems, I would soak them in a VERY dilute solution of detergent and warm water for 20 minutes, and then run a shank brush through them thoroughly until no more visible tars are evident draining out of the stem. Be careful with your choice of detergent though, because anything with bleach or any of the oxyclean type products will lift oxidation in your vulcanite stems. This isn't a big deal if you want to sand/buff and polish your stems; but will leave them discoloured and rough to touch if you don't polish the stems afterwards.
Then, in the absence of alcohol to clean the bowl and shank of your stummel, I would use the spoon from a pipe tool to scrape the bowl and remove dottle and any residual tobacco; then sand the cake layer down with 600 grit sand paper wrapped around a dowel. You can go back to briar if you want, but I'd leave an even cake layer of 1-2mm thickness. Then I'd use a brass bristled bore brush (often sold to gun owners for cleaning the bore of their weapons) to clean the inside of the shank.
That should get you a much cleaner pipe.
I hope that helps,
-- Pat
