Metallurgy in Oil & Gas Service: Brass and Ductile Iron 3

[ChEMatt]

(I apologize for the cross post, I posted in Gas Distribution but I thought after the fact this might be a better forum?)

Forgive my ignorance here. I got asked a question that I had not considered before so I don't have a good answer at the moment. Hope y'all can help.

Why is it we generally don't see brass or ductile iron in oil and gas (upstream or midstream) service? My first answer was that ductile iron probably has a tendency to rust and corrode a lot easier than carbon steel, but I am admittedly talking out of my behind, so to speak.

For sour, and non-sour services, why don't we see more of this metal in oil, water, and gas gathering, wellhead, well pad facility, separators, treaters, tankage, and midstream processing? Or do we and I never noticed?

Thanks folks,

-Matt

 

[racookpe1978]

Pressure, temperature, ductility (movement of the fitting or flange due to long periods of stress at high temperatures).

The metals are soft. To maintain the high loads under duress (fires as well) without failing, the higher alloy steels are preferred. Failure may be (not just bursting or tearing) but enough deflection so the bolts jam on disassembly of a flange, the gasket between two flanges doesn't seat, the valve body leaks by.

 

[MJCronin]

IMHO, brass is just too weak.... prone to external corrosion and expensive. The brass or copper bearing valves in the system can become very expensive and prone to additional maintenance.

Ductile (and Cast)Iron piping is sensitive to shock. There are many cases of piping failure (and death) where CI systems are used in steam/condensate service. Many piping codes warn against this. Many piping designers only use this material in underground systems. Corrosion resistance is developed in DI through increased wall thickness

Because of the pressure end thrust developed, underground Ductile Iron systems also require some type of axial restraint which can be expensive.

If the piping system can use carbon steel, it is usually the cheapest !!!

MJCronin
Sr. Process Engineer

 

[mk3223]

In addition, the allowed service temperature of the brass and iron material is lower than that of steel, and strength is also less. The other factors may be related to the fabrication, such as casting, welding, etc.

 

[ChEMatt]

Thanks folks. I appreciate your time and knowledge.

-m