Monel corrosion 1

[Q4K]

Did anybody have experience with corrosion on the upper trays in main column on CDU, made of Monel (alloy 400). Any experience with other alloys resistant to HCl and H2SO4 corrosion but also ammonia/amine attac also.

 

[Lee SiHyoung]

Please check if there is ammonium bisulfide deposition. Even if monel has good corrosion resistance relatively, it is very susceptible to aqueous ammonium bisulfide(NH4HS) corrosion. (Reference from section 7.2.4.4 and figure 9 of API 932-B)

For resistance materials recommended, please provide the detail information (ex., component, unit description, corrosive components concentration, temperature, etc.,).

Best Regards,

Lee SiHyoung
Engineer – Material & Corrosion Specialist
Tel : (+968) 22306214
Mob : (+968) 98891587
Email : lee.sihyoung@worleyparsons.com

 

[Q4K]

The minimum top temperature (most corrosive due to salt point)in main column on CDU is cca 120 C
Pressure is 1,3 barg.
The pump around reflux is pumped from the third tray to the first tray. The third tray is most corroded.
The corrodents based on the analyses of boot water from the overhead drum are chloride, ammonia, and H2S.

 

[pradipgoswami]

Monel(Alloy-400) is a very popular alloy for CDU overhead systems. I've dealt with fabrication of such towers, comprising of top 4/5 rows of trays made of alloy 400, as well as the top dome/dished head fabricated from C.S+3mm of alloy 400 cladding. Monel exhibits high resistance to many corrosion mechanisms in CDU, however may not be 100% immune. Following are the extracts of Corrosion damages of Monel from relevant refining industry publication:-

**D[highlight #FCE94F]issolved oxygen, at even small concentrations, often drastically increases corrosion of carbon steel, brass alloys, and alloy 400, all of which are often used in overhead systems. Alloy 400 is particularly sensitive to the presence of oxygen in acid service.
**[highlight #FCE94F]Alloy 400 can experience accelerated corrosion by H2S[/highlight].
**Oxygen contamination can accelerate overhead corrosion, especially on the Ni-Cu alloy 400.
**Alloy 400 performs well under shock condensation conditions if the overhead system is air free;
**however, [highlight #FCE94F]it can suffer from under deposit corrosion by chloride salts.
[/highlight][/highlight]
As one see the issues are complex, involving multiple factors. It may be a good idea to do a SEM/EDAX of the corrosion deposit, as well as failure analysis to get the comprehensive picture.

Look forward to your response.

Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299
All provided answer are personal opinions or personal judgements only. It's not connected with any employers by any means.

 

[Lee SiHyoung]

Referring to NACE Paper 34109 (2009 Edition), Crude Distillation Unit—Distillation Tower Overhead System Corrosion, it is as below.

Actually, monel is especially sensitive to "oxygen" in acid service. The typical source of oxygen is as below.

I) Oxygen ingress when equipment is opened during a shutdown.
ii) Oxygen ingress from desalter wash water.

 

[Q4K]

Thank you for your help and a ideas. The oxigen content in brine is around 0,6% wt at 30C but the the sample was not quite representative because the sampling conditions. Regarding the SEM/EDAX deposit analysis (from inlet chamber of air cooler) I have question: is the sampe representative if decontamination with chemicals and steaming was performed before sampling?

Thanks in advance

 

[EdStainless]

Your samples may not be representative, but they may still tell you something.
Oxygen in these systems needs to be very low, you need to look at how you are degassing the water and where you may have air leaks.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[pradipgoswami]

The corrosion deposits should be SEM/EDAX-ed in as it is condition, so as to get the best idea or RCA of damage.

Depending on the crude origin and overall chemistry crude column over head systems may experience:
--Aqueous Organic Acid Corrosion
--Ammonium Chloride Corrosion
--Hydrochloric Acid (HCl) Corrosion
[highlight #FCE94F]--and many other forms of corrosion.[/highlight]

Monel 400 is an extremely proven alloy to resist corrosion in acidic medias, however according to API-RP-571, it's prone to pitting damage in Ammonium Chloride. I would think it would be good know or control the "Salt Content" of the crude and have effective desalting in place. The same issues are discussed in NACE Publication 34109, “Crude Distillation Unit - Distillation Tower Overhead System.

Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299
All provided answer are personal opinions or personal judgements only. It's not connected with any employers by any means.

 

[rscosta1976]

Hello,

I've encounter severe corrosion of Monel trays in CDU unit due to formation of chloride salts. Under-deposit corrosion was very severe with all active planels being replaced every 4 years. Reasons behind the formation of salts was clearly established, however due to service restrictions it was not possible to eliminate it by changing the operating conditions.

For this particular, case it was decided to upgrade the top trays to alloy C-276.

Regards,

 

[nickypaliwal]

As stated above, Monel is not good for H2S service however our client standard option for all thermowells in carbon steel pipes in upstream industry is Monel 400. Advise if there is any limitation since it is not restricted as per NACE MR0175.

 

[Q4K]

Sanchern,
How did you establish salts formation?

Thank you

 

[pradipgoswami]

Use of Hastelloy C-276, for trays or cladded heads for CDU overhead systems with severe corrosion problems are well documented in NACE , API and other Oil and Gas Major's Operating procedures/best practices.
As per one refiners data, Hastelloy C-276 report extremely low corrosion rates as against Monel(Alloy-400). However for C-276 in addition to cost the long lead time is a point to consider. A good and efficient desalting facility is essential and may minimize the subsequent salt related corrosion in the CDUs.

Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[Lee SiHyoung]

nickypaliwal,
Please note that NACE MR 0175 is handling only one type of cracking as sulfide stress corrosion cracking among various kinds of corrosion. Although it is within the limit from NACE MR 0175, it does not ensure the suitability of all of the other types of corrosion.

Normally, considering the mechanism around this issue is localized corrosion, some specific corrosive environment can be concentrated in local spot (such as pitting). Therefore, consideration of process parameters cannot cover the localized condition. (Because, if there is stagnant zone, the concentration for corrosive component can be much higher than the level we would expect.)If monel is to be used, process control should be supported rather than checking the suitability of MOC from NACE MR 0175.

As it were, this kind of mechanism can be prevented by selection of C-276. However, C-276 might not be only way for the prevention. If monel is being used for some other fields in the world, that means process control such as oxygen ingress or salt formation needs to carefully monitored.