Malleable Iron Fitting Rating 1

[butelja]

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?

 

[Matador]

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.

 

[butelja]

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.

 

[MJCronin]

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 &quot;Certain types of malleable iron have low ductility characteristics and may be subject to brittle fracture&quot;. 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 !!!!

Regards............................................MJC
See ASME B31.1 paragraphs 124.5 and references