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We have a corrosion problem in our hydrocracker unit high pressure fans (reactor effluent air coolers). There are three water pumps in the unit and by using one pump, water injection rate is 20m3/hr (by design). Recently, we encountered corrosion in the fan tubes and shut down unit five times in one year for repair. Sulfur and Nitrogen content of fresh feed is a little above design. Can anybody help us? Might it help if we increased water injection, using two pumps simultaneously? Has anybody experience in of this?
 
Answers
22/12/2010 A: mohamed ali, EPROM/Midor refinery, mhassan@midom.com.eg
you can refer to API RECOMMENDED PRACTICE 932-B
This recommended practice provides guidance to engineering
and plant personnel on equipment and piping design,
material selection, fabrication, operation, and inspection practices
to manage corrosion and fouling in the wet sections of
hydroprocessing reactor effluent systems
23/10/2008 A: Vikrant Chopra, Shell Global Solutions, vikrant.chopra@gmail.com
Such corrosion problems in reactor effluent air cooler are typical to hydrocracking and hyrotreating units. Problem is usually due to low wash water rates or poor water distribution due to which the ammonium salt is not fully flushed from fin fan piping causing corrosion. We have experience of running two pumps simultaneously for similar reasons. There are couple of things which should be ensured
First check that velocities in air cooler piping and wash water piping with increased water rate is still below errosion limits.
Check that the pumps can handle the additional pressure drop in wash water piping due to increased flow (means pumps have sufficient head available to overcome this additional pressure drop)
We experience high vibration issue when we operated both pumps simultaneously. After investigation it came out that vibration was due to different pulsation dampners used in both pumps. Ensure that pulsation dampener are of same type and are working properly.
10/07/2008 A: Stefan van der Wal, Mettler-Toledo Process Analytics, stefan.vanderwal@mt.com
Typically for hydrocracking and hydrotreating processes ammonium bisulfide is the cause of most problems. In the case of ammonium bisulfide wash water velocity is one contributor that increases corrosion. The other more significant one however is pH. In case the pH is too high (!) corrosion increases exponentially. Good wash water pH control is vital. The measurement is however difficult due to the high pressure environment. We've got several installations that have solved the problem.
14/04/2008 A: SImone Robinson, Tube Tech International Ltd, simone@tubetech.com
The fact that you have had to stop 5 times in one year for repair indicates that the unit is suffering from severe corrosion. It is obvious you are battling from material damage and not from process flow limitations due to accumulation of corrosion products. Can you could provide more information about the process conditions?
09/04/2008 A: Hashim Rababah, Jopetrol, hsr978@yahoo.com
Check the percent of water injection about 5% from the fresh feed to prevent corrosion due to high velocity . check good distribution of water to all cells, and make sure there are no plugged tubes.
31/03/2008 A: Berthold Otzisk, Kurita¬†Europe GmbH, Berthold.Otzisk@kurita-water.com
Corrosion problems at the REAC (reactor effluent air coolers) are very common at hydrocracker units. Here the corrosion often results from the presence of ammonium bisulfide. The flow velocity is a key element and an increase of the wash water rate may help to improve the situation. A good flow distribution is important to avoid the deposition of solid ammonium bisulfide salts or the separation of vapour, liquid hydrocarbons and water.
Our proven ACF technology can help to significantly reduce the potential of ammonium bisulfide or ammonium chloride salts and we can offer very powerful corrosion inhibitors
31/03/2008 A: Mukesh Patel, Reliance Industries Limited, mukesh.patel@ril.com
Increasing Wash water may help you provided your system is designed for the increased flow resulting in increased velocity in pipelines. Operating two pumps in parallel will help since it will increase flow rate.
Flow distribution in air cooler also may be checked.
28/03/2008 A: keith bowers, B and B Consulting, kebowers47@gmail.com
Low wash water rates will lead to exactly the corrosion you are experiencing. This corrosion can lead to large leaks and spectacular fires that cause lots of damage and long down times for repairs. High pressure air coolers are custom built and not available from stock items.
Double the wash water rates immediately. The entire reason for wash waster is to prevent ammonium hydrosulfide deposits in the air cooler tubes. Uneven pitting type corrosion proceeds rapidly under the crusty 'carbuncle' appearing deposits.
You should also consult with your anti-corrosion chemical vendor and get a complete chemical analysis of the wash water exiting the air cooler. A filming type inhibitor may be necessary.