Q & A > Question Details
I have observed corossion in my crude overhead line to finfan coolers. The overhead line is not insulated and the temperature here varies from zero to 55 degree celsius. Would insulating the line help me in reducing the corrosion? What are the other impacts of overhead line insulation?
Note: We are operating the top temperature 25-30 degress above the dewpoint temperature.
12/05/2021 A: Jake Gotham, InSite Technical Services, jake.gotham@insitetechnical.com
The overhead line should not be insulated. Doing so is unlikely to resolve any internal corrosion but does introduce a risk of external corrosion under insulation (CUI).
18/04/2021 A: Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
In addition to all the above the following may also to be kept in mind: 1. Isolations for individual tube bundles for facilitating isolation and repair. I came across with some P&Ids that say these isolations are to be provided in future (after making a bit of money), but are ignored as this remains an unnoticed P&Id note. 2). Confirm it is a Corrosion issue not a result of erosion caused by the two phase flows (when continuous water injection towards neutralising the acid attack) is practiced. 3). Never ignore corrosion losses while doing the scope challenge of TA job list (towards optimising TA schedule) and retube all the suspicious bundles. Remember that these suspicious bundles have to live till the next TA.
25/03/2021 A: Suman Senapati, Hindustan petroleum Corp., sigma.6.2009@gmail.com
It is not insulated for a good reason. There are parts of your plant which are meant to dissipate heat. This is one such location. The fin fan cooler and the trim condenser are meant to bring down the temperature below 40 degC. So, insulating your vapour line would only increase your condenser heat duty.
The vapour line itself should not face major corrosion problems as long as your amine-based filmer chemical injection is in place, considering your vapour line temperature is well above dew point of steam at your operating pressure.
Strict control over your sour water pH (to be maintained within 5.5 - 6.5) should help with controlling the corrosion. Amine based neutralizing chemical injection needs to be used to control sour water pH.
If your plant has an overhead corrosion probe installed, keep an eye on the reading. Generally, it should not exceed 4.5 mils per year.
Also, do check your desalter efficiency. A low desalter efficiency generally increases risk of overhead corossion
25/12/2012 A: ali jazayeri, Bouali sina petrochemical complex, smajazayeridezfuly@gmail.com
We had similar problem in our complex. After many investigations we found the most appropriate way to reduce corrosion in this area is injection of filming amine inhibitors.
02/10/2012 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Is the problem area near the column or near the fin fan? Are you water washing, using filming amine, ammonia? The dew point calculation is inaccurate in this service. The better operation is to take full range naphtha overhead and split the naphtha in another column. Another superior design is to have an overhead vapor to crude shell and tube exchanger with the vapor in the tubes. The condensation of water occurs in the bundle which can be replaced due to leaks during TAR.
01/10/2012 A: keith bowers, B and B Consulting, kebowers47@gmail.com
Controlling corrosion of Crude Unit overhead line is well understood by Vendors of your various inhibitors When you say 'dew point', is that 'water dew point?' Insulating the overhead line may keep the pipe walls hot enough to prevent water condensation. However, that is not certain or suggested as a cure.
Crude Unit Overhear line corrosion is well understood and the Vendors of additives and de-salting aids are well placed to advise you in solving he issue. First stage is controlling the acidity of the produced sour water by adding either caustic or ammonia as needed, carefully monitored and controlled.
The best place to add the pH control depends on actual piping configuration, but ideally before any water condenses on the (cold) pipe wall.
Filming amines work well to reduce corrosion, but can get expensive if used to also control the sour water pH.
Many refiners monitor the iron content of the sour water to estimate corrosion activity. others use corrosion probes.
01/10/2012 A: Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
There are differing viewpoints on how to mitigate corrosion in the overhead line of crude atmospheric towers. Following are my suggestions when working with one-stage overhead condensing system [no tip top pump-around and no double drum system]
# Ensure overhead line is "gravity flow" from after top U-bend through to top inlet nozzles of air cooler condenser and 'gravity flow' from outlet into cold accumulator
# Inject filming amine just past top U-bend via metering pump to tee injector
# Incorporate engineered "artificial dew pointing" with respect to both WSR naphtha and sour water. Use tee quill injectors and individual FI/FC/FCV stations [This is often controversial]
# Control the pH of sour water [preferably using metering pump to inject anhydrous ammonia into artificial dewpointing water]. pH should not be allowed to become too low or too high [Check with chemicals supplier for suggestions]
# Add in-line coalescer to reflux flow to reduce its entrained and emulsified water content