No. The intention is to relax the rule on material selection and the tightness test due to a lower risk associated with fluids that are nontoxic, nonflammable and nondamaging to human tissue in case of leaks. one thing that the code always emphasize is safety (cant put premium on life andlimbs). In our piping spec, we have specifically deleted reference to Cat. D for process piping.

Note that alterntive test is also allowed under the rules of b31 in lieu of hydro. Faced with the same situation, ill go for a hydro.

Go with a hydrotest every time steam is involved.  I don't believe the spirit of the code was ever intended to include steam in cat. D service.  Strictly speaking it is the Plant Owner's responsibility to determine what fluids will be considered as cat.D or M, although the owner can pass on this responsibilty to his agent (i.e. his design contractor).

In what I have seen, category D ends up being plant air, instrument air, cooling water (although the chemicals in it might make it not Cat. D) and potable water.  Not much.  Pretty much ends up stuff you could swim in and be o.k.

Certainly, I have NEVER seen steam listed as Cat. D.

Would you want to have your face anywhere near a leaking flange in steam service ?  I really doubt it.

Richard Thompson, P.E.
Pipe Stress Engineer
Houston TX
S&B Engineers and Constructors, Ltd.

Wow.  There sure seems to be a big fear of steam out there.  Remember, we are not talking about 900# steam here.  I personally would not want to get hit in the face with steam or high temperature liquids.  I agree that in general, a steam system should be hydrotested.  However, in the case of revamp work to existing piping, there might be a few welds that are not practical to hydrotest.  If these welds were located such that a leak would not be blowing directly in somebodies face, and they were not in a confined area, I think it would be legitimate to call the steam Category D at that particular location just for purposes of performing a service test.

I know these welds could be covered by performing them as closure welds, but we all know how busy those welding inspectors get during a shutdown.  I'd rather have them standing next to the dissimilar metal weld that's going to see hydrogen at 1000°F than a weld in a rack that will see steam operating at 82psi and 250°F.

Anybody ever use the concept of a "localized" Category D service before?

Hello,

There seems to be a general misunderstanding of the B31.3 concept of "Fluid Service".  There IS NO SUCH THING IN B31.3 AS A CATEGORY D (or any other caregory) FLUID, per se.

From paragraph 300.2:
"Fluid Service:  a general term concerning the application of A PIPING SYSTEM, considering the combination of fluid properties, operating conditions, and other factors which establish the basis for design of the piping system.  See appendix M".  The fluid service concept was introduced in recognition of the broad coverage of the B31.3 Code.  The fluid service concept allows the code to assign various appropriate levels of rigor to the design, fabrication (and erection) and testing of piping systems.

So it is ALL these things (the combination of fluid properties, operating conditions, and other factors which establish the basis for design of the piping system) that must be considered in determining the fluid service category.

Clearly, the fluid service concept applies to the system in its entirety.  It is either category "n" or it isn't.  

B31.3, paragraph 300(b)(1) assigns the responsibility to the owner of designating the fliud service for the piping system .

Just my opinion.

Regards, John.

Good reply John.  After going through and reviewing the definitions of ALL the words in the definitions (not just "damaging to human tissue"), I am in agreement on the comment about fluids vs. fluid services, and that i can't treat a specific location in the system differently just because it is isolated.

Thanks for setting me straight.  This discussion has given me some ammunition for when the inevitable "But we've done it this way for years," comes at me.