Steam Piping

1) There is paste, and there is paste -- and there is dope and there is putty.

Proper paste for the application does not leak - improper paste always leaks. (It's in the definition of "proper")

Get the right paste and put it on properly.

fwiw, I had an installation where the cast iron bosses were so bad from every clown in the food chain having to do an inspection, pulling the brass plugs from the iron bosses and the ports being resealed each time with sealants/tape without regard to corrosion or inspections, that eventually tape wouldn't hold the seal. I had to use "the yellow stuff", and it worked just fine at stopping corrosion and sealing the ports.

2) And not to be too obvious - this is an engineering group, and there are a couple of cardinal rules of engineering, like

"if it worked before and it doesn't work now - go back to what worked"

proviso - "unless you are damn sure what you WERE doing will eventually cause a lot more damage than the new method"

fwiw

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For specifications on the tape:

For a discussion on "make up" instructions: The tape should be applied 1.5 to 3 wraps, put on as if you were threading on the female part (so when you install it, the tape gets wrapped tighter, or at least not "balled up"). The tape acts primarily as a thread lubricant, so that you actually get the threads fully mated prior to metal-to-metal engagement. If the threads are high quality and clean, I've only ever had to use teflon tape. In general, "pipe dope" is only required if the threads are:

- going to be made / unmade a lot, or

- in bad enough shape that tape alone won't allow sealing, or

- there are dissimilar materials involved, with temperature swings that can loosen a joint.

I have used teflon tape and silicone sealant together with good effect. I was doing ozone added to cool water though. Silicone sealant is only good to ~180oF max. I think the combination of tape and dope is the right choice for marginal (aka. non-virgin or commerically formed) pipe mating surfaces.

I don't find any ANSI / ASME standards that will help you on the web, the "eng-tips" link referred to "B.120.1", but I don't find that text on the web... you might poke around "B.12" and see what it says about sealants. Most online references say "A or B", without offering "A and B" as a valid choice.

I hope that helps.

David A. Smith