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Malleable Iron Fitting Rating

Malleable Iron Fitting Rating

Malleable Iron Fitting Rating

I am looking for more detailed information on the pressure-temperature rating of ANSI B16.3 class 150 malleable iron (A197) fittings.  I have information stating that they are rated for 300 PSI from -20°F to 150 °F, and 150 PSI @ 366 °F (saturated steam).  What is the maximum service temperature that these are permitted to be used at per B16.3?

RE: Malleable Iron Fitting Rating

We only specify this material for natural gas (70 psi) systems & we use screwed fittings. Our 150 psi @ 367F steam systems use A105 GrII. We use B31.1 code we use and I couldn't find it there.

However, I have an old pressure vessel design manual which has the material listed as part of B31.3-1976.

ASTM 197, Cupola Malleable
Minimum Tensile Strength = 40,000 psi
Minimum Yield Strength = 30,000 psi
Minimum Temperature = -20
Allowable stesses (SE) in table @ different temps.
From 0 to 650F = 8,000 psi
Above that nothing. There are several notes accociated this material. I don't have the actual code, just a few pages.

RE: Malleable Iron Fitting Rating

Thanks for the reply.  Our specs specify A105 fittings for all steam services as well, and only allow A197 on air lines.  

I was asked to evaluate a used drum warmer that had these fittings as part of the steam coil.  Obviously it is only good for < 150 PSI saturated steam.  The pressure-temperature rating comes into play for determining the setpoint of a pressure reducing station.  However, since our 200 PSI steam is superheated, even with the reduced pressure, I will still have superheat to deal with.  The rating will have to be <150 PSI because of the superheat, but I don't know by how much.

RE: Malleable Iron Fitting Rating

Butelja & Matador......

Boys, boys, boys....... when in doubt, consult the piping code. There are limits on the use of Malleable Iron fittings !

In paragraph 124.5, ASME B31.1 states "Certain types of malleable iron have low ductility characteristics and may be subject to brittle fracture". The limits for malleable iron are 350 psig and 450 F.

B31.1 also wisely limits the usage of this material on Boiler Blowoff and Blowdown systems ( systems that are subject to sudden thermal shock)

B31.1 also doesn't want you to use these fittings in toxic or flammable gas service....

For a couple of dollars more, I would ALWAYS go with the forged carbon steel SA105 fittings instead of malleable or ductile iron.

Hope this helps !!!!

See ASME B31.1 paragraphs 124.5 and references

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