Screwed fittings for steam pipe

[jakhsl]

I am replacing some short sections of 1" steam pipe (6 barg saturated steam). The service seems to be well within the pressure-temperature ratings of malleable iron fittings - 20 barg @ 300 oC - but I notice the unions I am replacing are 3000 lb, and possibly the other screwed fittings. Also I perceive a bit of negativity towards malleable iron fittings for steam...

Can anyone tell me why malleable iron fittings should not be used and if it is necessary to use all 3000 lb for this service? (all fittings are screwed)

 

[kacarrol]

There is a pretty good discussion in the following thread regarding iron vs steel in steam systems:

http://www.eng-tips.com/viewthread.cfm?qid=165632

For the fittings suitability have a look at the manufacturer (or code) pressure and temperature tables, also the bore of the fitting and how it fits up with the bore (schedule) of your piping.

K

 

[MJCronin]

jakh.....

ASME B31.1 Section 124.5 contains limitations on the use of malleable iron in power piping systems. It is subject to brittle fracture at high temperatures and is restricted by B31.1 to systems operating below 350 psig and 450 F.

Malleable Iion has further restrictions to usage in certain non-boiler systems by other paragraphs contained in B31.1.

What is your code of construction for this project ?

Do you have a piping "material spec" for this system and does it permit malleable iron components at 300 C ?

 

[jakhsl]

Many thanks for your replies ... we'll be using forged steel fittings + sched 80 pipe for this, it's just that there seemed to be a bit of a assortment of fittings in the sections being repaired - no doubt down to replacements over the years! I guess whatever the codes say, the malleable iron fittings are pretty cheap and nasty ...

J