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# Flare pipe material selection

## Flare pipe material selection

(OP)
thread338-270504: HIC and SCC tests could they be done on stainless steel?
Hello ,
for horizontal flare (flare piping - buried to burn pit):
during flare scenario, MDMT is -95 deg C and service is sour with 5110 ppm of chlorides and 3.5 % H2S. pressure is 35psia. Client prefers to select alloy 625 pipe material. Now question is about last spool (around 12 m) including so-called flare tip (which in fact is pipe open end itself), process team calculated 1650 deg C and material has to be selected for this high temperature spool. i believe this last spool will have very less pressure like atm to 5 psia. i need your advice regarding possible materials which could withstand this temp. service is occasional only during startup. i think SSC and SCC is not a concern at such a lower pressure. i have seen SS310 flare tips and pipes up to some lengths in vertical flares but i dont have experience with such a situation and high temperature pipe. kindly share your experiences with similar situations. thanks in advance. are below options practical? design life is 20 yrs.
1. SS310
2. Inconel 625
3. Inconel 600

### RE: Flare pipe material selection

Flare tips tend not to be designed for continuous full flame exposure, thus 1650 deg C is a fair way beyond the normal operating range of typical flare tip materials. Throw in the H2S as well and it becomes a tough ask to select a suitable material. Perhaps, re-examine the design and process calculations to see whether the temperature can be brought down in some way.

Steve Jones
Corrosion Management Consultant

All answers are personal opinions only and are in no way connected with any employer.

### RE: Flare pipe material selection

There is usually excess air or steam injected into the flare, part of the reason is to lower the tip temp.
310 is the least expensive
625 will have the highest strength
600 will resist sulfidation and carbonization the best

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P.E. Metallurgy, Plymouth Tube

### RE: Flare pipe material selection

(OP)
Thanks Steve Jones and EdStainless.
I discussed with process and they confirmed the temperature of the flare last spool is maximum 1100 deg C. initially they provided the flame temperature which was also surprising for me.

Here the question is now " what is your opinion to use SS310 (NACE). I am concerned about Cl-SCC externally because of high temperature. my opinion about internal Cl-SCC is that since oxygen is not present so Cl-SCC is not a concern internally. Externally pipe is buried and some portion is above ground in burn pit area. process confirmed that around 12 m spool will undergo 1000 to 1100 deg C). This flare will be used only during only initial start-up and in case of any downstream process interruption. there is no flare KOD and this is wet sour gas directly coming from well head. can we take credit of short well life say around max 10 years we will have approx. 5 times flaring as worst case.
just to summarize ( H2S: 3.2%, CO2: 6% , chlorides 2000 ppm and 5200 ppm) two chlorides because two different cases.
Client insists on 625 or reasoning for SS310. (do you think external coating for SS310?? and which one?

### RE: Flare pipe material selection

Cor-Mat
For burn pit flare piping in gas plants, Incoloy 800 is generally used. Then, of course, economics plays a big part, specially if you take credit for short well life.

### RE: Flare pipe material selection

The issues that I have seen with these are related to the fact that you run them, get them scaled and dirty, and then they sit for months/years. When they get used again all of the corrosion products get blown off. After just a few of these cycles you can loose a lot of metal. I have a hard time seeing 310 or even 800 having enough corrosion resistance to withstand the long periods of idle.

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P.E. Metallurgy, Plymouth Tube

### RE: Flare pipe material selection

(OP)

EdStainless,
thanks. so probably applying expensive zirconium oxide coating is not worth for shorter design life. it will be better to keep SS310 with a repair/replace strategy in place?


### RE: Flare pipe material selection

I would recommend the RA 253 alloy and repair/replace as needed. We used this material for our coal burner tips.

### RE: Flare pipe material selection

External SCC, or other damage mechanisms, could also occur in the buried portion, so attention will have to be paid to corrosion control selection for that region. With H2S, oxygen is not the issue for internal SCC, thus it would remain a corrosion threat in the zone where liquid water can still be present. However, what is the risk associated with a failure in the high temperature portion - is it imperative that this portion does not fail under any circumstance whatsoever? If a failure, and the associated failure mode(s), is tolerable, then pick the alloy that will provide the basic function of conveying the fluid with the lowest lifecycle cost allowing for replacement(s). If failures are not tolerable, then a robust, and usually more expensive, alloy needs to be selected which is where your client is heading with their N06625 option.

Steve Jones
Corrosion Management Consultant

All answers are personal opinions only and are in no way connected with any employer.

### RE: Flare pipe material selection

A general question, do people not use centrifugally cast material for these applications?
The alloy selection is much greater, alloys based on the HU (20%Cr 40%Ni) composition have been used in heat treat applications for decades where high temp and exposure to S and C are issues.

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P.E. Metallurgy, Plymouth Tube

### RE: Flare pipe material selection

(OP)
Thanks Steve Jones. i presented the case to Client exactly on LCC basis.
i just want to have clear understanding of your sentence below:
"With H2S, oxygen is not the issue for internal SCC"

KR

### RE: Flare pipe material selection

The absence of oxygen will not rule out SCC in an H2S containing environment. On the other hand, if O2 does enter then the issue will become that of elemental sulphur.

Steve Jones
Corrosion Management Consultant

All answers are personal opinions only and are in no way connected with any employer.

### RE: Flare pipe material selection

In my experience both AISI 309 and AISI 310 series are more than enough considering that are specifically applied for high temperature service and very resistant to creep and corrosion at high temperature service. Moreover are the more used for flare application cause of the high temperature service.
The inconel 625 is more specific for high cloride and h2s partial pressure, but is not the case, in fact both Chloride and H2S is relative low compared to the services typically used for Inconel 625 material.
The partial pressure of CO2 and H2S is not so high so the inconel 625 is in my opinion to much for such application.

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