Stainless to copper transition for fire stopping 7

[Boiler1]

Hi All,
I’ve noticed a copper spool fitted to otherwise stainless-steel pipework. The length of the spool was approx. 10 pipe diameters and the installer’s explanation was that the spool is installed to stop the fire spreading inside the pipe.
Is this a good practice or a legislative requirement? Could a flame arrester be used instead of a copper spool?
The materials are connected via a brass flange on the copper side which probably acts as a dielectric union. The fluid in question is the Oxygen.

Regards

 

[MJCronin]

Boiler ...

You must understand that oxygen systems are quite unique and the gas makes those systems subject to possible internal fires . No other commonly used industrial gas poses this hazard !!!

The United States of America has done much research in past decades regarding safe handling of both gaseous and liquid oxygen. This takes the form of NASA SAFETY STANDARDS .... used for decades throughout the world. Potential internal ignition mechanisms and ignition sources have been researched.

http://brcompliance.com/wp-content/uploads/NASA-Oxygen-Standard-I.pdf

Copper and some copper alloys are suitable for use in oxygen systems at all pressures. Copper can be particularly useful for resisting ignition by particle impact ... but only when the whole system is made of copper

What I believe that you question regards is something called a "Fire stop" ... It is an old practice ...

It is discussed in this document:

http://asiaiga.org/uploaded_docs/AIGA 021_12 Oxygen pipeline and piping systems.pdf

Fire stops are short spool pieces of copper or nickel-based alloy. Their use is no longer considered common practice in steel pipeline transmission or distribution systems.

Smaller devices (called "flashback arrestors") exist for industrial gas systems. They are mandatory for oxygen and acetelene service. These are designed and certified specifically for smaller HP oxygen systems.

https://www.linkedin.com/pulse/flashback-oxygen-acetylene-systems-danger-crew-vessel-kjell-hagen/

I do not understand the mechanism by which a short section of copper pipe can protect against internal fires in an entire oxygen system

Best Regards




MJCronin
Sr. Process Engineer

 

[chicopee]

Oxygen is not a flammable gas. Oxygen only supports combustion, so the purpose of the copper spool inside the pipe mystifies me.

 

[bcd]

Three things needed for a fire. Oxygen, a fuel, and ignition. In your pipe, iron in the stainless is the fuel. So there will not be "a fire in the pipe", the fire will be the pipe. It will simply melt away if there is an ignition source. Usually a small particle that moves in the flow stream down the pipe and impacts a iron containing part. The particle needs to be moving pretty fast to cause the ignition. When the pipe is burning, it simply melts away until the fire reaches copper or nickel-copper (Monel) material. Then it stops.

 

[EdStainless]

I recall these discussions when we were installing a system.
The arrestors that we installed were basically spool pieces (SS just like all of the piping) filled with a coarse Cu wool.
People used to install Cu or Monel spool pieces plain steel piping in order to stop burning of the steel itself.
Given enough oxygen and ignition source everything will burn.
That is what makes oxygen so scarry to work with.

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P.E. Metallurgy, consulting work welcomed

 

[FacEngrPE]

The spool is a fire break. The pipe is the fuel. Copper pipe can still burn, but the ignition temperature is higher than it's melting point.

The ignition source can be as simple as shavings in the pipe, and the velocity being high enough that the grit hitting the inside of an elbow creates a momentary hot spot,

If you are building or maintaining oxygen piping systems these documents explain the hazards well.
ASTM G128 Standard Guide for Control of Hazards and Risks in Oxygen Enriched Systems
ASTM G88 Standard Guide for Designing Systems for Oxygen Service

Oxygen Safety: Swagelok provides some of the scary information discussed in the astm documents. Document is attached.

 

[EdStainless]

I forgot the link to the CGA site.
G-4 (and all of the sub-documents) are oxygen related.
G-4.4 id specifically piping systems.

https://portal.cganet.com/Publication/index.aspx

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P.E. Metallurgy, consulting work welcomed

 

[Boiler1]

Wow! Thank You all for great comments! I would have replied individually if there was an option.
As to the purpose of the copper spool and the mechanism how it works, I believe the idea for the spool is to melt down and stop the fire that way. I have only seen the flame arresters doing the same.

Regards