Corrosion on Hot fuel gas

[adilmn]

Good Day Gents,
One of the Hot gas line(2" Fuel gas) in my plant getting corrosion and leak continuously where there are low points. Externally pipe surface is in good condition and no thickness reduction. But it experienced localized corrosion on some location where there is low points.
Even after the line replacement with new material also getting the same issue with a time span of max 1 year.
Material is carbon steel

Is there any possibility of gas condensation on low point section which will lead to corrosion?
What are the key factors which will lead to corrosion on hot gas line except material defects.?

 

[Dhurjati Sen]

Dear adilmn,

1. How old is this corrosion issue? Is it a recent phenomenon or did it start right from commissioning, etc.?

2. Where are you getting this fuel gas from? Was there any process change?

3. Is the line insulated? (Sure it is) Is it steam-traced?

4. Can you test the fuel gas for %H₂S & %H₂O ?

Regards.

DHURJATI SEN
Kolkata, India

 

[adilmn]

Thank you Mr.Dhurjati Sen for your reply.
1. How old is this corrosion issue? Is it a recent phenomenon or did it start right from commissioning, etc.?
One year before i have experienced same corrosion and leak which was replaced with new pipe spool. Now again the same location affected with internal corrosion.

2. Where are you getting this fuel gas from? Was there any process change?
There is no process change

3. Is the line insulated? (Sure it is) Is it steam-traced?
No, it is neither insulated nor steam traced.

4. Can you test the fuel gas for %H2S & %H2O ?
Already requested for sample to check the moisture presence. I will add the H2s also.

Have you any detailed idea regarding the condensation chance with the hot gas lines especially at low point section?

 

[Dhurjati Sen]

Dear adilmn,

Point no 1 is not clarified. Is the line 1 to 2 years old?

Point no 3 is so important. Request 'Process Dept.' for a review of this line. It is not an inspection / corrosion issue.

Point no 4 would be useful for Process Engineers.

You may close this thread and re-post the same in 'Chemical Plant Design & Operations Forum'.

You would get appropriate advice from experts like Georgevarghese Sir.

Regards.

DHURJATI SEN
Kolkata, India

 

Are you seeking a failure analysis?
Go to a metallurgical lab for that.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[weldstan]

How hot is hot? What is the operating temperature range? Is operation constant or intermittent?

 

[adilmn]

I am not looking for a Failure analysis from the lab. My concern to know more about the chance of hot gas condensation at low point sections.
What are the reason may behind the hot gas condensation.
As i mentioned, line is on service from last 10 year and low point section experienced with corrosion from last two years. Ist time on 2018 we have changed the affected spool with new one and again after one year the same issue occurred.

Line in constant service with temp of 268 degree F and it is not insulated yet.

 

[Chumpes]

Hello
Corrosion of CS @130°C happens because wet conditions occur. Condensation does not necessarily occurs at low points only, but low points collect and store corrosive water, leading to corrosion at low points.
Water condensation occurs because the water content is too high (?) and temperature is too low (no insulation) :
- what is water content ?
- what is water dew point temperature ?
- do you have a margin over water condensation temperature ?

Specification of a slope, no low points, free draining, and thermal insulation would probably help achieving extended operation for this line.
Regards