Wer H2S at elevated temperatures debate

[hussaindawki]

Hey guys,

I am having today three scenarios entitling the wet h2s cracking consideration:
1- I am having a stream at HCU operating at 230 Deg C and pressure of 2200 psia, with water fraction of 0.38% but as per the heat mass balance no liquid H2O flowrate is present, so shall we consider wet H2S cracking following NACE MR0103 that it may happen at elevated temperature due to the formation of monoatomic hydrogen that will be in action during shutdowns? noting that licensor did not consider it.
2- in the same unit there is amine stripper gas, contains about 1.17xE-4 of H2S mole fraction at pressure of 2100 psia and temperature of 70 deg C, the H2O content is about 0. 1% H2O, this stream data after compressor, as per the HMB no water flow rate is present, so shall we consider also wet H2S cracking following NACE MR0103 threshold?
3- in CO2 capturing and transportation, the pipeline is in supercritical condition at pressure of 3720 psia and almost ambient temperature, the H2O is present as 0.04% and H2S partial pressure is around 2.5 psia, as per the flow assurance no water formation will happen at all cases, because the dewatering before compression maintains the water content below 0.5% H2O, so in that case shall we consider this damage mechanism or not?

Generally this case repeats many times for example in GOSPs at the gas compression section discharge to the aftercooler, usually the interconnecting piping would be free of water.

What do you think guys? It would be a great help for me to have a solid justification.

 

[hussaindawki]

Any thoughts guys?

 

[EdStainless]

Please clarify, the documentation shows that there should be zero water, but in actually you have various small amounts of water in the process.
Is this correct?

 

[Trestala]

The total sulfide species content in aqueous phase will need to be calculated to determine if you'll meet the threshold (see NACE MR0175 Part 2 Annex C).

 

[hussaindawki]

Please clarify, the documentation shows that there should be zero water, but in actually you have various small amounts of water in the process.
Is this correct?

Hey Ed, the document is the heat mass balance coming from the process system as per their model or software we can say, it mainly says no H2O based on dew point and relative humidity to check the saturation

 

[hussaindawki]

The total sulfide species content in aqueous phase will need to be calculated to determine if you'll meet the threshold (see NACE MR0175 Part 2 Annex C).

The funny part is not water flow or aqueos phase present as per their model due to the temperature or unsaturation, so the process cannot give me a value because there is no aqueos phase present during operation

 

[SJones]

You are attempting to perform a corrosion risk assessment based on simulations and assumptions (most likely of normal operating conditions). What is your precise issue: keeping the cost down by not specifying sour service? Look at all possible process scenarios, the possible progression speed of the damage, and the consequences of a failure. Does it really cost too much to simply say H2S = sour service, and sleep easier?

 

[hussaindawki]

You are attempting to perform a corrosion risk assessment based on simulations and assumptions (most likely of normal operating conditions).

Yes indeed it is in the design stage. Btw, is it not recommended to work on the max operating conditions?

What is your precise issue: keeping the cost down by not specifying sour service? Look at all possible process scenarios, the possible progression speed of the damage, and the consequences of a failure. Does it really cost too much to simply say H2S = sour service, and sleep easier?

The client always asks about the reasoning behind, due to cost optimization

 

[SJones]

Is it not recommended to work on the max operating conditions.

Until the process safety system settings are finalised, the max operating conditions will be guesswork too. It will also depend on the risk tolerance of the assessment in terms of the expectation of how rapidly the damage mechanism will initiate and progress. This leads some to use design pressure and temperature in their considerations provided that these have not been set in a deeply conservative manner with massive margins over maximum operating.

The client always asks the reasoning

The client should be setting the rules of the assessment, so the reasoning would be theirs.

For your CCS pipeline query: Review Paper

 

[hussaindawki]

Is it not recommended to work on the max operating conditions.

Until the process safety system settings are finalised, the max operating conditions will be guesswork too. It will also depend on the risk tolerance of the assessment in terms of the expectation of how rapidly the damage mechanism will initiate and progress. This leads some to use design pressure and temperature in their considerations provided that these have not been set in a deeply conservative manner with massive margins over maximum operating.

The client always asks the reasoning

The client should be setting the rules of the assessment, so the reasoning would be theirs.

For your CCS pipeline query: Review Paper

Thanks Mr Jones for elaborative response, I would agree with you that for any cracking damage design conditions shall apply. However, the client specification enforces us to only utilize the maximum operating condition, even after we discussed with them, they said follow our specification!

I will read the paper you shared.

Regarding refineries, I noticed that licensors do not consider sour conditions for reactors and even separation drums for instance the hydrocracking, hydrotreating and isodewaxing units. We have raised that concern while reviewing their preliminary material selection, they justified their stance by the normal operating conditions and by applying proper shutdown to purge the system during temperature decrease at shutdown. If possible can you give me your opinion in that regard?

 

[SJones]

Their rules. Their problem if it doesn't work out.

I'm not really a downstream afficionado, but I would get Technical Safety involved as to their view on relying upon an operating procedure to create inherently safe conditions versus picking a material with resistance to the failure mode.

 

[hussaindawki]

Thanks Mr. Jones