Flare tip material selection 5

[nickt1960]

Our contractor, has passed on the following response from the flare manufacturers/designers.
There is some H2S in the LP & tank farm flare streams (0.01 and 0.04 mol% respectively) which the vendor indicates will be a problem for the nickel alloys (800, 625) and as such they propose 310/316 for better corrosion resistance. The proposed emergency flare tips will be 310 but the vendor is proposing 316 for the operational flare due to its expected lower temperature.
Experience suggests that Alloy 625 and 800H are the peferred tip materials.

In particular, we have the following questions.
1. Is Alloy 800H to be susceptible to these levels of H2S?
2. Would 310 provide adequate service in place of the Nickel alloys?
3. What is the maximum temperature for 316? The actual grade of 316 has not been stated, but we would think that 316H would be proposed which may create welding issues with the higher carbon content.
For the application of 316 piping, we would expect that a TSA coating would be applied to protect against CSCC.
Any other thoughts or suggestions would be appreciated.

 

[EdStainless]

I presume that they are not wanting to use 625 due to cost, and at todays Ni and Mo prices I agree with them. However, they are talking about a huge step down in performance. Why not 800 or even 825. 310 has a lot of Ni and it won't be a lot less expensive than 800. If you want a little better corrosion resistance 825 might be a good compromise.

The problem htat I have seen with flare tips isn't in operation, but when they are shut off and subject to the normal environment. The corrode a little and then that layer blows off during operation. Over a while you can loose a lot of metal that way.
310 ins't bad at high temp, but it doesn't like cyclic oxidation.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[peteship]

Flare tips require a material resistant to high temperatures, at least for the top part of the tip.

310 and 800H both meet this requirement, 316 does not, and 625 is marginal. 800H has the highest temperature resistance, but in my experience 310 will give the longest tip life in arduous conditions. In refinery and petrochemical service, flare tips are expected to last 5 years without shutdown. 316 should not be used for flare tips - the marginal saving in cost will be more than cancelled out by short tip life.

310 and 800H are adequate for H2S service, 316 is not so good. 625 has good corrosion resistance, but is very expensive.

All materials for H2S service should be certified to NACE standards MRO175 or MRO103.

 

[SMF1964]

It may be that they are concerned about the high nickel content reacting with the sulfur in the environment at high temperature. Nickel and sulfur form a low melting point phase at (I think) 900° or so. Above that, the stuff is liquid and you end up with serious wastage - as fast as the reaction can occur, it turns to liquid.

 

[rolledalloy]

At elevated temperatures high nickel alloys will form a nickel-nickel sulfide eutectic this is molten at temperatures around 1150F. This eutectic causes the normally protective chromium oxide layer on the surface to become porous, non-protective, and leads to rapid metal wastage.

Alloy 625 at over 60% nickel could have problems. 310 at 20% nickel in general is much better in high temperature sulfur bearing environments. 800H at 32% nickel would fall in between. 825 at 40%+ nickel would be a concern. Higher chromium levels tend to be beneficial in resisting sulfur attack.

That being said there are other issues that we hear about. One is polythionic acid stress corrosion cracking. This can occur when temperatures are low enough, such as during shutdowns, etc. For this reason something that contains a stabilizing element like Cb or Ti would be helpful.

The other issue is strength at low fire or when winds cause the flame to impinge on the flare's side. In these situations hot spots can cause distortion of the flare tip. 625 and 800H are both quite strong compared to 310 and 316 so there will be a sacrifice in strength if 310 or 316 is substituted.

If the temperature is low enough 347 or 321, which are stabilized, might be a better option than 316. They also offer better strength than 316L.

Compared to 310 an alloy like RA 253 MA would offer nearly two times the creep strength. This is a result of alloying with nitrogen. At 11% nickel, RA 253 MA is better at resisting high temperature sulfidation attack and is also a little lower in price than 310. RA 253 MA is not stabilized.

 

[PVRV]

a. H2S is not a concern for the selection of flare tip
material.

b. SS310 is superior to 800H.

c. SS316 is inferior to both SS310 and 800H.

d. 600 is superior to SS310, check the Cr content.


Cheers

 

[SJones]

PV,

On what basis is "H2S not a concern for the selection of flare tip material"?

On a related note, from researching materials for our high H2S, miscible gas injection EOR project, we learnt that our Canadian colleagues use 310 protected by a thermal spray zirconia thermal barrier coating.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[PVRV]

SJ,

The flares are open to atmopshere.

How is a thermal barrier coating related to H2S.

Cheers

 

[SJones]

PV,

The H2S will still cause sulphidation of susceptible materials and has to be a consideration in materials selection albeit not from an SSC point of view. It can also lead to to polythionic acid SCC if the material becomes sensitised.

The thermal barrier is not related to H2S per se and I was quoting it as an actual application. It is applied to prevent the repeated cycle of atmospheric corrosion during inoperative periods followed by removal (erosion) of corrosion products during operation.

All the best.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[PVRV]

SJ,

Sulphidation & Polythionic acid SCC if the material is sensitised

At what conditions?

 

[SJones]

Operating and shut down (don't forget some flare tips are of welded construction) ;-)

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[PVRV]

Good Man and solid Engr.

 

[SJones]

Always good to have a bit of

technical

Keeps us on our toes

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[SheryH]

Hi, SJones:
Is the ZrO2 thermal barrier coated on the operational flare tip or the emergency one? Where can I find a supplier for the YSZ thermal barrier coated of flare tip?

Thank you!

SheryH

 

[SJones]

Sorry, I don't know either the flare operating mode or the supplier. I would expect that the tip suppliers probably subcontract the coating work so best to contact the usual players:

http://www.flareindustries.com/products/offshore-flares.asp

http://www.gba-flares.com/flaretips1.htm

http://www.johnzink.com/products/prod_kaldair.htm

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/