Q & A > Corrosion
Date  Replies
17/07/2014 Q: Need all your expert views on crude oil Basic N2 impact on fouling tendency. This is limiting on crude flex/ optimization as the refinery has CAM limit for basic N2 (150ppm). Need to understand the fouling tendency of Low N2 crude whether this is credible or perceived. Also understand the fouling tendency/reversibility. If credible, please provide if there are ways to mitigate (eg: every low N2 crude processing is followed by crude that can act as cleaning and recover any loss in duty?)
Low basic N2 could be good for LRCCU feed and also hope for HCU where as this limit could restrict such crudes from buying/processing… We always used to be on the basis of waxy vs. asphaltic… every waxy run followed by a aromatic/naphthenic crude run to provide cleaning effect. Antifouling was other alternate only in LR circuit and /or SR circuit.
Blending of crude based on compatibility to mitigate was another option…
There should get some clear guidelines for mitigation if the impact N2 is credible and proven… can you provide any such details and what is minimum technical solution for such mitigations as this will be a clear big lever for crude flexibility.
(1)
23/06/2014 Q: Has anybody got idea about which metallurgy to select in wash drum outlet line to nitrogen dryer package in CCR. Currently we are having SS 316L metallurgy but because of chloride carryover we are continuously facing problems of localized pitting. Hence we need to upgrade metallurgy such that it should be effective and at low cost.  
02/05/2014 Q: What are the pros and cons of adding Caustic at the upstream of Desalter? (2)
04/04/2014 Q: We are processing local crude in which sulphur content is very less....Light naphtha is being separated from pre-flash tower...for corrosion control we are using filming amine...the iron content in boot water of naphtha reflux drum is within range...but chlorides are reporting more that 50 ppm... we are also using wash water that is recycling from booth water to the inlet of overhead condensers....what should be the maximum allowable range of chloride content in naphtha reflux drum?
(4)
27/03/2014 Q: In the CDU Desalter can we use one demulsifier for different Crudes. Is it possible to test effectiveness of the Demulsifier in Laboratory? (1)
25/03/2014 Q: What should be the quality of Desalter wash water make-up?
Please clarify in terms of Hardness, PH , H2S,Alkalinity and Chloride content.
Deaerated water is not available only limited quantity of Boot water from accumulator is available.
(1)
25/03/2014 Q: We are frequently observing chocking of crude column overhead boot water pump strainer. There is no sign of of high iron or solid contaminants in boot water and other parameters (like pH, chloride, fe ) are within limit. Please suggest if any one has faced such type of issue. (1)
21/03/2014 Q: Refinery Practice is to add Demusifier at the upstream of Desalter. But some Refineries also inject Demusifier at the Suction of Crude Charge Pump. Which is better? (1)
04/03/2014 Q: What quantity of iron scales is likely to be generated normally from internal cleaning of Naphtha tank of 10 TMT capacity (18.5 m height) when taken for maintenance after nearly 10 years of continuous service in a Petroleum Refinery?  
19/02/2014 Q: After around 5 years services, material Hastelloy C276 (sch 10S) is cracked near the weld (HAZ). The service is HCL. Actually is line is used to upload 32-36% HCl on the tank. (Temp ~ 35C).
Can you please tell what is cause for that leak?
 
05/02/2014 Q: Is there any SO2 production due to decomposition of Sulfolane use as a solvent for aromatics extraction? (2)
08/01/2014 Q: Lately, have been experienced tube leak in DHDS stripper feed-effluent exchanger, Tubes were plugged and hydro-tested.
Four months later, again leak developed and found tubes in bad condition, and was recommended for full bundle re-tubing.
I would like to know what could be root cause for this tube failure in short time? Any specific improvement need to be done on internals of exchanger?
(5)
25/12/2013 Q: What is salt point at crude overhead? (1)
25/12/2013 Q: We are observing an increase in crude column boot water chloride while the processing of RAS GHARIB crude in higher %. The frequent excursions in chloride up to 40 ppm has been observed during the period. It also lowers the boot water pH.The iron values are within specs. It is understood that this crude contains the organic chloride in it which cracks in the furnaces and increase the chloride concentrations. The increase in caustic flow in the downstream of desalter is also not helpful. Kindly share the processing experience. (1)
07/12/2013 Q: What the causes of naphtha diluted in water boot of overhead? visually water boot carbonized and foaming. (1)
06/12/2013 Q: Working in a production plant aromatics. The unit of liquid-liquid extraction using sulfolane as a solvent. High corrosion rates are presented and are now breaking equipment. Successful cases could help me with this problem and problem of corrosion in sulfolane?

Additional info: Thanks for your answer. Actually we have a problem with oxigen in water system. The primary solvent( wet) is black color and foaming. whitout suspended solids. What best practices have been applied to detect and remove the air inlets in the vacuum system?
(6)
05/11/2013 Q: What are the main constraints in proper corrosion inhibitor selection for CDU (naphthenic crude oil)? (1)
17/10/2013 Q: We have heard in many technical forums about ‘Unit Quench Factor’.
We would like to know more on this term, monitoring experiences, correct technical formula & accuracy of this term in predicting stress build-up in coke drums.
What are other ways for monitoring stress on coke drums? Are there any standard references/values for water quenching, steam quenching & vapour heating - rates and Deg C/Min?
 
11/09/2013 Q: We are not using wash recycle system in CDU. Is there any drawback to that? (2)
05/09/2013 Q: We operate our DCU main fractionator with Top Pr. 0.57 Kg/cm2g & Top Temp. 99 Deg C. We process VR with more than 5000 ppm normally. Recently column DP fluctuated a lot and we suspected salt deposition in trays. Steam was increased and DP become normal. Queries are:
1. How to calculate salt sublimation temp? What parameters I need to look into?
2. How to estimate salt quantity?
3. What are reasons for salt generation in system?
4. What kind of salts are expected - organic or inorganic?
5. Is it possible that if salt sublimes once and again it becomes vapour once temp increase ie. is phase reversal possible?
6. What are industry best practices to remove salts deposited?
7. Is there any way to avoid salts formation in system or avoiding ingress?
8. Any crudes responsible for high salts or its caustic dosing at crude desalters?
 
30/07/2013 Q: We are currently experiencing continued plugging of our refinery fuel gas control valves, strainers and burners. We went through a re-org 3 years ago where one of reformers was brought down. Since then, we have seen an increase of chloride salt contaminants to our fuel system from our other reformer. We currently run 2 molecular sieves in series on or hydrogen header. I proposed to increase heater reliability and reduce chloride salt contaminants to take second mole sieve and pipe the fuel gas header to it. This would of course be after testing hydrogen chloride content with only one sieve in service and projecting those results on compressor reliability from our maintenance group. If no real future damage can be projected and current single phase mole sieve can handle hydrogen system, would a mole sieve for the fuel gas be an adequate route since the vessel is already there and would only require a piping mod?  
27/06/2013 Q: Our termosiphon reboilers in SWS unit are corroded after only two years. Column works fine, but the tubes in reboilers are leaking, lids are corroded, full of deposits etc. Pipe from bottom of stripper column to reboiler is plugged, almost 90%. Results are poor quality stripped water (with high H2S and NH3). Tubesheet material is SA 266 Gr.2, tubes SA 179 and shell SA 516 Gr.60.
Shell side (LP steam): 180C deg.
Tube side (stripped water): 130C deg.
What could be the problem?
(2)
11/06/2013 Q: The unstabilized naphtha streams from our CDU preflash and crude columns and off gases from hydroprocessing units are processed in Saturated gas plant (SGP). Processing separate out the gas and liquid products by a combination of compression, cooling and fractionation.
The gases are compressed and combined with hydrocarbon liquid, cooled in a high pressure receiver to separate the mixture into vapor and hydrocarbon liquids.
The vapor after C3,C4 recovery and amine treatment is sent to fuel gas system while the liquid hydrocarbon rich in Naphtha/LPG is pumped to Stripper followed by naphtha stabilizer and finally naphtha splitter to split naphtha into Heavy naphtha and light naphtha.
The Stripper is a reboiled 32 tray column with top tray feed provided to remove C2 and lighter components from the liquid product.
The stream composition and process condition of stripper overhead vapor is as follows:

Stream Description - Stripper OVHD
Stream Phase - Vapor
Total Molar Rate KG-MOL/HR - 1,021.58
Total Mass Rate KG/HR - 46,931.65
Temperature - C 87.15
Pressure - KG/CM2G 10.3
Total Molar Comp. Rates KG-MOL/HR
H2O 12.02
H2 26.49
NH3 0.78
H2S 205.46
METHANE 18.78
ETHANE 179.66
PROPANE 200.35
IBUTANE 91.72
BUTANE 153.85
IPENTANE 33.23
PENTANE 36.16
CP 0.02
C6+ 63.05816096

We are not injecting any corrosion inhibitor in stripper overhead stream. Is it a concern? Should we be dosing a corrosion inhibitor in stripper overhead stream based on the ammonia, water and H2S levels in stripper overhead?
(1)
20/04/2013 Q: In one of the client refineries which we are working with, they are facing severe corrosion in the 2nd and 3rd stage ejectors of the vacuum column. The current treatment program is adding CI and neutralizer before the 1st stage ejector and during inspection/shutdown there has been no corrosion observed in the 1st stage but huge corrosion observed in the 2nd and 3rd ejectors. Is there are any similar kind of issue faced in other refineries. If so what has been the solution measure taken?
(2)
12/03/2013 Q: Some weeks ago we saw some cracks in the FCC expander blades in one of our FCC units. The cracks appeared suddenly, from one month to another.
The fresh catalyst addition rate are very low, so catalyst turnover is slow. It has provoked the ageing of our e-cat inventory. We have measured the attrition of the e-cat, with Jet Cup method (Davison Index), and there is a decrease from 2-3 to 1-2. My question is could this decrease in DI of the e-cat (harder catalyst) be responsible for the mechanical problem in the expander?
(2)
02/01/2013 Q: We are currently using overhead sour water as wash water for the crude overhead system which is injected just before fin fan coolers. Neutraliser is injected into the vapor line before water injection point. Will injecting neutraliser in wash water line help reduce corrosion in crude column overhead system? (4)
04/10/2012 Q: As per section 11.1.3 of API 574:
"In low-pressure and low-temperature applications, the required pipe thicknesses determined by the Barlow formula can be so small that the pipe would have insufficient structural strength. For this reason, an absolute minimum thickness to prevent sag, buckling, and collapse at supports should be determined by the user for each size of pipe."
Table 6 of the same code provides some data for Carbon and Low-alloy Steel Pipe at less than 205 degree centigrade condition.
My question is how this strength is measured and in case of temperature higher than 205 degree centigrade what are the values?
 
27/09/2012 Q: We run a bitumen blowing tower producing off-gases (toxic gases) which we exhaust to an incinerator. What is the recommended material for the valves used in this service?  
26/09/2012 Q: 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.
(4)
17/09/2012 Q: If caustic dosing suspended due to some unavoidable reasons is it possible to reduce overhead corrosion (caused by hydrochloric acid) by increasing amount of neutralizer like ammonia or amine at overhead of the Atmospheric distillation unit?
(3)
17/09/2012 Q: What is the expected life of fin tube of overhead air cooler of Atmospheric distillation unit? (1)
17/09/2012 Q: What is the expected life of polyurethane seal of floating roof storage tank?  
16/09/2012 Q: AMOC have NMP unit, the outlet pipeline of the solvent recovery tower is changed from time to other as a result of corrosion although the acidity of the solvent is adjusted by soda ash and the material is carbon steel.What are the reasons of corrosion in this part of the unit ?  
25/07/2012 Q: Please give us any suggestions for the online cleaning of Vacuum column overhead condensers. The Condensers are suspected to be fouled. What can be the fouling material in the condensers? (5)
17/07/2012 Q: In our refinery the tubes of aero-condenser (air-cooled heat exchanger) suffers a remarkable thickness reduction. In January, 2009 we have replaced all the tubes with 2.77 mm thickness. During routine shutdown in October, 2011 we had found that thickness reduced dramatically. We had recorded the lowest thickness of 1.4 mm. At that time we had replaced the bottom layer of one bank which contains that tube.
After that one tube of adjacent bank was plugged due to pinhole type leak. A few months later expansion groove of one tube of this bank found corroded. We had taken few sample thickness in June, 2012 and got minimum thickness of 0.9 mm.
We found that only rear end tubes are facing significant thickness reduction. Again there is no vent or drain nozzle/plug in the rear header so it is not possible to clean the header properly during shutdown. After investigating we also found that the dosing of corrosion inhibitor and caustic soda suspended for several times due to unavoidable circumstances.
My question is what are the main reasons (including dosing interruption) behind the thickness reduction and what is the expected service life of tubes and header of aero-condenser?
(2)
30/06/2012 Q: I am trying to build a model to optimize the operation of Crude Desalter and study its effect on Crude Column Overhead Corrosion.
The major salts present in Crude are NaCl, MgCl2 & CaCl2; but in our laboratory we measure only Total Salt Content of Crude (before and after Desalter); we do not measure individual salt.
My queries are:
1) How the individual salt affect Desalter performance and Crude Overhead corrosion
2) Is it required to measure the individual salt's content in Crude?
3) Can I assume some typical break-up of individual salt (Note that the type of crude we process changes very often).
(1)
20/04/2012 Q: We are facing a great problem with our pipelines near cooling tower. The water vapor/mist from cooling tower causing corrosion of these pipelines. We are using enamel paints but did not help us much. Please help me to find out a solution to protect the pipelines from the corrosion.

(2)
22/03/2012 Q: I am working in DHT Plant diesel hydrotreater unit and face a proplem with Tempered water system that show the Iron High in Tempered Water System and make Troubleshooting we drain the system many time and make chemical cleaning some time it gone ,but after time it come High
we Drain the system completely to remove any residual contaminants and Isolate the amine sample coolers for one week and cleaning and Add N-2819M to achieve a molybdate.
how do we solve this problem with the Iron and PH.
What is the source of the iron coming ??!!
(1)
17/03/2012 Q: In the refinery sour water stripper, ammonia content is 90 ppm vs deisgn of 50ppm. ph of stripped water is high @9 and this is being reused in desalters as wash water. Due to this, in our CDU overhead system, the boot water pH is reamaining high in the range of 7-7.5 without any injction of neurtraliser. Will this affect the CDU over head system from the point of view of corrosion? And is it required to dose any neutraliser to CDU overhead in this case? Also, is it ok if the desalter wash water has 9 ph? (3)
10/03/2012 Q: We are fractionating the feedstock from natural gas condensates into Naphtha, Kerosene, gas oil and residual stream. The overhead condenser of the first distillation tower suffers from very bad corrosion. The fact is we are not desalting the incoming feed, due to the salt content is 0.5~1.5 ptb based on ASTM-D3230 test result. We only inject the neutralizing and filming amine to the condenser inlet header instead of feed desalting.
Upon condenser outlet piping replacement we found a huge amount of sludge sitting inside the old-thin piping. The sludge is >95% Fe.
The questions are :
1. Does ASTM D-3230 also reflect the Sulfates salt in the feed stock? Because the water boot contains total S more than total Cl. We worry that Sulfates salt also being hydrolyzed to produce h2SO4 that corrodes the overhead piping. If sulfates salts are also create corrosion problem than how to check the salt content other than Cl salt?
2. Beside chloride content, what are to be checked in the feedstock before deciding to stop desalting? What is the method to check?
3. We plan to install a water wash system in order to prevent sludge deposition and under deposit corrosion. The problem is the condenser pipe header is non balanced type ( E manifold, not C manifold). We are in doubt whether the water will be evenly distributed to all branch to condenser inlets.
(2)
13/12/2011 Q: My question is related with a problem of copper corrosion strip failure (ASTM-D130) in gasoline. We have two tanks of off-spec gasoline:
- Copper strip corrosion 3B; SH2=0ppm, mercaptans = 9ppm. Does not improve copper strip corrosion test adding corrosion inhibitor
- Copper strip corrosion 2C; SH2=0ppm, mercaptans = 5ppm. Improves copper strip corrosion test adding corrosion inhibitor
My questions are:
- Could the low level of mercaptans present cause a failure in copper corrosion strip?
- Could a NaOH carryover from the Merox unit cause a failure in copper corrosion test?
- Any other sulfur compound, besides SH2 and mercaptans, could cause this copper strip corrosion test failure?
- Does anyone know any commercial additive for mercaptan removal that could be useful for this problem?
(5)
25/11/2011 Q: Swivel joints are used in the roof drain line of the floating roof tank. In our refinery we usually replace these during repair work on the tank. In that case the life of the joints is about 10-15 years. But I want to use these joints again. There is no testing facility for these joints. There are 20 swivel joints in each tank so a good amount of money is required to replace them. My questions are:
1. Is it a good decision to replace the joints after 10-15 years?
2. How should we test the joints if we wish to use them again?
 
26/10/2011 Q: The following query is regarding the MEG solution circulation system in Propylene Recovery Unit (PRU).
PRU unit has a vent condenser at the downstream of DeEthaniser. Vent condenser typically operates at 3 ~5 degC. 30% MEG solution in DM water is used as a refrigerant. Metallurgy followed in this MEG solution circulation system is carbon steel. During start-up, if DM water is received in the circulation system (which is having a surge drum - with nitrogen blanketed), is there a possibility of corrosion due to DM water contacting directly with carbon steel? Is it a good idea to maintain slight nitrogen atmosphere (may be around 50 mmWC of nitrogen pressure) in the surge vessel before making up DM water? How best this MEG solution system can be commissioned avoiding corrosion?
(2)
12/10/2011 Q: In our Butadiene plant we are using ACN+Ethanol+Water(tertiary) solvent. IN WASTE GAS RECOVERY EXCHANGER we observed there is a formation of ammonia salt.Tube side is HC(EA+VA+BD+small trces of ACN). Due to corrosion regularly the exchanger is leaking. Shell side is Brine (water+MEG). The exchanger is operated at around 10-15 degree celsius. Even bottom pump casing is damaged because of that material. Please suggest a solution. (1)
09/08/2011 Q: What are current views on twisted tube heat exchanger configurations in refineries, particularly in comparison with conventional shell and tube configurations? (6)
25/07/2011 Q: We have a crude unit with a double drum overhead system. The first drum collects the HC condensed from the hot section exchangers and returns all condensed HC as reflux to the crude tower. The vapor from the first drum (reflux drum) is sent to the cold section where all the HC and water is condensed and collected in the second drum (distillate drum). Any noncondensible is sent to gas recovery section. From the design conception, water should only condense on the second drum, however, we are seeing condensation (and corrosion) in the reflux drums as well as the overhead vapor exchanges heat from a relatively cold crude. In addition, we have seen signs of salt deposition and eventual corrosion in the other exchangers where water dew point is very unlikely. Given these problems in the hot section exchangers, what can we do to address and prolong the life of our overhead condensers? Please take note that the water wash, filming inhibitor and organic neutralizers are only added in the cold section exchangers going to the distillate drum. (3)
07/07/2011 Q: We have a CDU with (a preflash tower), the top product in which naphtha vapors are cooled down using a series of horizontal air coolers (vertical air flow). A corrosion problem was noted days ago in some tubes, knowing that this air cooler is only 6 years old in service while another series of air coolers used for the same object but with another CDU with (a preflash drum) for 23 years now and they work well, at least better than the stated one.
We use Ammonia as demulsifiers int desalter in both units.
(3)
26/06/2011 Q: While working as an inspection engineer I faced some questions which answers are not clear to me. Please help me in this regard:
1. We are taking thickness record as per previous locations. I want to know how the locations are selected to record thickness on the pipe lines.
2. Sometimes we found higher thickness from the previous record. In this condition we recheck the thickness. Is there any alternative or tolerance limit?
3. How the retiring thickness of the pipe line is calculated?
4. Is there any suggestion while inspection of pipe line commenced?


(3)
07/04/2011 Q: We are facing problems with the main fractionator reflux drum bootwater high chlorides(120 ppm)
There is prefractionator ahead of main fractionator but we are getting zero chlorides in overhead boot water.
does the inorganic chlorides dissociate more at temperatures greater than 250 degC which is prefractionator temperature?
(3)
04/04/2011 Q: Our overhead wash water which is demineralised water addition is not continuous at CDU plant. Water is added to 2 bundles in 4 hrs. Then water is added to the next 2 bundles and so on. This implies that the 1st bundle in which water is added receives wash water after a gap of about 1.5 days. We use neutralising amine and keep ph between 5.5-6.5 while having almost no corrosion on overhead lines (monel cladded). Caustic is also added at the downstream of the desalter. The contractor who provides services and chemicals is claiming that addition of more wash water to have continuous wash will decrease the consumption of neutralising amine. In our opinion this will not work since the amount of wash water will have no impact on the mass of chlorides available in overhead stream. Would you please comment. (4)
01/03/2011 Q: Our Delayed Coker Unit Fractionator boot water chloride content is ~240ppm, Iron content ~0.22ppm. We have started injection of DM water at the upstream of condenser. What is the desirable range/ its consequence and how to reduce it ? What is the root cause and contributing factors for high chloride?

Additional info:
Vacuum residue is the feed to DCU and its water content is 1.2-1.4%.
(5)
28/02/2011 Q: To avoid corrosion in NHT Stripper overhead circuit, what should be range of PH in overhead receiver boot? and what should be the temp of overhead condensing stream to receiver at around 10.5ksc press? (2)
08/02/2011 Q: I am trying to identify a substitute for caustic soda in a desalter. My client wants to reduce his caustic spend volatility. Is there anything available which serves the same purpose as caustic and is as price competitive? (1)
11/01/2011 Q: In Continuous Catalytic Regeneration (CCR) plant we have faced a corrosion problem at the downstream of regeneration section which was caused by chloride ion contained vent gas. What are your suggestions to prevent corrosion? (4)
04/12/2010 Q: We are facing problems with one of our reforming unit furnaces. There is a common duct in the three furnaces. The damper of the middle furnace is causing the problem. This damper falls several times after burning. The skin temperature of the tubes remain good but the stack temperature is higher than safe value by almost 150 degree Celsius (around 900 degree Celsius) . The furnace outlet temperature is operated below the design temperature by almost 25 degree Celsius. Our design temperature is 525 degree Celsius. The shaft, plate of damper used of stainless steel grade. We had changed burner tips several times but the problem was not solved. Please suggest me the cause and remedy of this problem. (3)
09/11/2010 Q: Can you please advice what type of corrosion inhibitor, biocide, antifoulant and polyelectrolyte polymer can be used in Desalter effluent? (4)
22/10/2010 Q: We have LVGO stream from vacuum column & processing it in VGO hydrotreater. In LVGO stream we encounter chlorides up to 20 ppmw (organic+inorganic) which is posing corrosion issues in VGO hydrotreater. I want to know how to remove these chlorides prior to enter downstream unit. (6)
25/07/2010 Q: Are variable speed drivers ever used in pumps?
If not, why not?
(4)
06/07/2010 Q: What is the best way of judging the efficiency of a desalter? (6)
21/05/2010 Q: What are the likely effects of water carry over from desalter on Crude heater and distillation column? What steps should be taken if this happens? (11)
21/05/2010 Q: I am working on CDU as a field operator.
I want to know why NH3 or NH3H2O is injected in overhead line of distillation column?
Why dont we use NAOH for nutralization there? Even NAOH is cheaper then Ammonical water.
(5)
19/05/2010 Q: Does installaton of static inline mixer in place of conventional mix type globe valve for mixing the wash water and crude before desalter help in improving desalter efficiency? (4)
18/05/2010 Q: Does injecting wash water ahead of preheat exchangers improve desalter efficiency? (3)
30/04/2010 Q: I know butt welding is much stronger than lap welding. But I found that the bottom and roof of storage tanks are welded as lap welding. What is the reason behind this? (1)
13/03/2010 Q: The purpose of Caustic injection in Crude is maximization of conversion of MgCl and CalCl into NaCl. Can anyone explain how this happens? (3)
13/03/2010 Q: Please highlight procedures for removal of iron deposited on Zeolite Resin of conventional water softeners. Any vendor who could suggest chemical for this purpose?  
03/03/2010 Q: What are the implications of shell side fouling on the pulling of a VCFE/Texas Tower (Platformer) bundle for cleaning? Our client is looking to pull a VCFE which has been in-situ for 16 years and I would like to find out if others have carried out a similar exercise and any impacts fouling may have had on the activity. (1)
09/02/2010 Q: We want to by-pass our de-salters in order to check the consequences with and without desalters on CDU. Moreover we have stopped de-emusifier dosing prior to desalters. What impacts are anticipated in your opinion and what parameters to be monitored in case when there is no desalter in crude preheat trains? (9)
06/02/2010 Q: Recently we are facing topping unit furnace inlet becomes lower than expected. The normal temperature is 215-220 degree centigrade. But now we are getting only 200-205 degree centigrade. What are the probable reasons behind this? And what measures should be taken to overcome the problem? (6)
06/02/2010 Q: When calculating heat exchanger shell thickness according to pressure vessel formula it is found that the required thickness always much less than the original existing exchanger. I want to know the reason behind it. (2)
08/01/2010 Q: I want to know the temperature profile of post weld heat treatment for alloy steel like P5, P9. We have some procedures that was used from a long time. I want to know the source or reference of the temperature range. Please suggest the maximum temperature, holding time, temperature raising rate, cooling rate. (1)
08/12/2009 Q: We have a catpoly hydrotreater that converts olefins to paraffins to produce petrol diesel and jet fuel. I just want to know the reaction/chemistry that should take place in the poly hydrotreater and the kinetics associated? (1)
07/12/2009 Q: What is the retiring thickness that leads to the replacement of the process pipes of various schedules? Is there any standard? Or it is based on experience? (1)
07/12/2009 Q: How do you calculate "salt point" of an atmospheric crude distillation tower overhead system containing full boiling range naphtha? (1)
23/11/2009 Q: The needs are:
to know the methods used to study corrosion rate in seabed sediment
so far I got to know 2 methods but I don't have the details of them:
method 1 weight loss method
method 2 transplanting and burying method.
any information on the above issue could help greatly
 
21/11/2009 Q: In our refinery we want to introduce an inspection software for data and history keeping purpose. Can anyone give me suggestion which software will be useful to serve the requirement?  
19/11/2009 Q: We are experiencing corrosion of a side stream in coker fractionator. Earlier used CS pipe was replaced with SS-321 pipes which failed due to pitting corrosion.
Does anybody have similar experience? What is the probable reason of the failure?
(3)
18/09/2009 Q: As a load bearing member which one is better: H beam or I beam? Is there any design criteria to select the appropriate beam?  
21/08/2009 Q: In recent days we have found that in our refinery the bottom/lowest course of the crude tank is severely corroded, especially the lowest one metre. We intend to replace the bottom course without replacing other courses. the course height is 1829 mm. the diameter of the tank is 69 m. the thickness of the bottom course is 20.0 mm and the immediate above course thickness is 17.0 mm. The height of the tank is 12 m. We will also replace the annular plate and bottom plate. Can anyone help me which will be the right procedure to replace the course? (2)
31/07/2009 Q: I am doing some research on the Cameron acquisition of Natco and was interested in learning if desalters are sold in the United States. My understanding is that they are installed in refineries when the refinery is built and inasmuch as there is no new refinery construction there are no desalter sales in the USA. Is that correct? (3)
29/07/2009 Q: What is the best way to calculate Ammonia injection rate in Crude distillation column? (4)
03/06/2009 Q: What is the reaction chemistry behind the formation of Ammonium Bisulfide salt and how does the deposition take place with respect to temperature? (3)
20/05/2009 Q: We are planning to carry out new Aux. HP steam Boiler hydrostatic test. Currently we do not have any demineralised or soften water available on site except with portable water via water tanker from desalination unit supply by contractor. (New Plant)
1) What type of chemical should be added to this water and in what concentration?
2) How do we dispose of the used water after hydro test?
3) After draining the boiler, how do we dry up the superheater tubes? Is using dry instrument (tool) air acceptable (no N2 easily available on site)?
 
17/03/2009 Q: Are the declining costs of metallurgy providing an incentive for construction of 2000+ ton heavy-walled hydrocracking reactors? Is the application of advanced manufacturing techniques, such as Cr-Mo vanadium welding, becoming the 'norm' for fabrication of heavy walled hydrocracking reactors? What other developments coincide with new hydrocrackers designed to operate in a highly corrosive environment? (1)
25/02/2009 Q: What are the merits and demerits of re-using spent caustic from Meroxes back into crude at the upstream of CDU? (1)
17/11/2008 Q: Can we inject caustic at upstream of De-Salter instead of downstream? What will be the consequences? (6)
07/07/2008 Q: Under what circumstances is it cost effective to revamp the FCC main fractionator so that the amount of heavy FCC naphtha feed to ULSD hydrotreaters can be increased while still meeting finished ULSD product flash and distillation requirements? Are most ULSD hydrotreaters designed with a three-product stripper using a fired heater, or is a simple steam stripper adequate? (1)
12/05/2008 Q: How much is the Min. and Max. allowable amount of Hydrazine in the demineralized water closed loops as an oxygen scavenger?  
29/04/2008 Q: How does the quality of wash water affect the desalting of crude? what are the parameters based on which quality of wash water is decided for desalting? (2)
27/03/2008 Q: 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? (8)
17/02/2008 Q: Can anybody tell me the cause of increasing algae and bacteria in a cooling water system? (2)
04/02/2008 Q: What are the problems faced in Overhead of CDU Condenser, and why do such problems occur?
(2)
05/01/2008 Q: Recently we are observing low lubricity in Ex. Merox treated ATF. The merox unit is UOP. The ATF lubricity Ex. CDU unit is 580 to 600 microns whereas after merox reactor and thereafter it remains 710 to 740 microns.
Can anyone please advice what will be the possible remedy to improve lubricity Ex. Merox unit?
(1)
23/12/2007 Q: Double drum crude fractionator has frequent leaks in the crude/overhead heat exchanger. The water used is recycled water from the second drum boot containing H2S in high concentration. The purge-out is only to the quantity to the steam added to the fractionator. Is this water, rich in H2S, being used for washing the main cause of the leak? Will stripped water make up in good quantities help? If yes, how much stripped water should be used? The vapor entry in the condenser is side entry instead of the usual top entry. Could this change in configuration also be the reason? (2)
04/11/2007 Q: Neutralizing amines are used in PH control in crude distillation over head systems to minimize corrosion. While studying the possibility of using such amines for Vacuum distillation several contradictory points of view appear some approving and some objecting. What do you suggest? We currently use ammonia in our vacuum distillation.
(2)
06/09/2007 Q: I am working in a solvent extraction-based unit for benzene production, we opened the unit’s extractive distillation column after a year of operation to troubleshoot the reasons for high pressure drop (2 barg), where we found a thick layer of heavy, coked material on each tray. Feed for the unit is reformate from a CCR unit (4% benzene). What are the possible reasons for this?” (4)
06/09/2007 Q: In the off gases from our vacuum distillation column hydrogen % has been up to 30-35% by volume.This vacuum unit is mild severity dry distillation with designed VGO end point of 510 deg C.
The overhead boot water PH also remains on the lower side (~5) even though the neutraliser is added in large quantities (more than 100 ppm). The same neutraliser has used earlier for the same type of crudes.
Has anyone had this type of experience? What may be the reason for the same?
(1)
05/09/2007 Q: In a Crude distillation unit using hot reflux and with a two stage desalter, repeated corrosion has been found in the Crude / Overhead vapor exchanger leading to tube failure. The crude /Overhead vapor exchanger is the first exchanger in the crude preheat train which heats the crude received from storage (at ambient temperature) using hot vapors from crude column. The MOC of subject exchanger is carbon steel and continuous dosing of filming amine, neutralising amine and wash water (stripped sour water used as wash water) is done. The exchanger is a horizontal floating head shell and tube with vapor on shell side and crude on tube side. The crude processed is Middle East. What are the possible causes and remedies to overcome repeated tube failure? (5)
17/08/2007 Q: In our naphtha hydrotreating unit, iron contents in stripper overhead boot are being reported on higher side for the last month. So far we have tried the following:
1. Increased corrosion inhibitor injection from 3 wt ppm (design) to 7 wt ppm.
2. Replaced the corrosion inhibitor
3. Cold condensate injection in reactor effluent increased from 3 to 5.5% of feed.
But iron contents are still high (2~3 ppm).
What could be the possible cause and what is the solution?
(4)
31/07/2007 Q: Recycle gas compressor of CRU had ammonium chloride salt deposition in its impeller vanes during regeneration activities. Can we wash the rotor with DM water or steam condensate without opening the machine. If yes, can you suggest some guidelines?

(4)
09/07/2007 Q: What are some of the recent advances in corrosion and fouling control technology that are being applied in the industry? Where in the processing industry are these programmes most effective? (5)