Now you can print posts from Chemical Professionals

Dear Visitors
I have installed printing option for printing of the individual posts, so that you can use them later on as a reference or for any other use. This will remove all the widgets from Blog & only post text is printed.

To print a post, do the following.

1. Click on th etitle of that individual post.
2. Once it is completed loaded go to the end of post (Not to the bottom of your screen).
3. Just at the end of my words of post you will find a printer icon with 'Print this post' link on the left side.
4. Click it & you will find your printer selection pop up in few seconds.
5. Print & keep them without having any sidebar, blog header etc.

Thanks for your co-operation & appreciation.

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Pumps - 50 Troubleshooting Tips

All of us as a process engineer face different problems related to pump operation. Be it a problem of low capacity, low head, pump loosing prime,

requires excessive power, stuffing box or seal leakages which are very common, bearings life, overheating etc.

All these problems are critical if the pump is in process fluid service which is either corrosive or hazardous. Therefore a step by step approach is necessary to attend to these problems. Recnetly I came across a compiled list of such 50 tips which I am sharing here for you. Note down these tips & follow them whenever you get any pump problem for troubleshooting.
Pumps are rotary devices which converts velocity or kinetic energy into pressure energy for compresible fluids to pump them from one location to the other. Being a rotary device they are prone to general wear & tear problems therefore, a process engineer should know how to handle these problems & do effective troubleshooting.

Here is the list of 50 such tips for pump troubleshooting categorized into different heads.

• Suction Troubles


1. Pump not primed.
2. Pump or suction pipe not completely filled with liquid.
3. Suction pipe lift too high.
4. Limiting pipe size in suction or higher velocities resulting in flashing.
5. Insufficient margin between suction pressure and vapor pressure.
6. Excessive amount of air or gas in liquid.
7. Air pocket in suction line.
8. Air leaks in suction line.
9. Air leaks into pump through stuffing box.
10. Foot valve too small.
11. Foot valve partially clogged.
12. Inlet of suction pipe insufficiently submerged.
13. Water seal pipe plugged.
14. Seal cage improperly located in stuffing box, preventing sealing fluid entering space to form seal.


• System Troubles


1. Speed too low.
2. Speed too high.
3. Wrong direction of rotation.
4. Total head of system higher than design head of pump.
5. Total head of system lower than design head of pump.
6. Specific gravity of liquid different from design.
7. Viscosity of liquid different from design criteria.
8. Operation at very low capacity.
9. Parallel operation of pumps unsuitable for such operation
10. Incorrect piping layout.


• Mechanical Problems


1. Foreign matter in impeller.
2. Misalignment.
3. Foundations not rigid.
4. Shaft bent.
5. Rotating part rubbing on stationary part.
6. Bearings worn.
7. Wearing rings worn.
8. Impeller damaged.
9. Casing gasket defective permitting internal leakage.
10. Shaft or shat sleeves worn or scored at the packing.
11. Packing improperly installed.
12. Incorrect type of packing for operating conditions.
13. Shaft running off center because of worn bearings or misalignment.
14. Rotor out of balance resulting in vibration.
15. Gland too tight resulting in no flow of ;liquid to lubricate packing.
16. Failure to provide cooling liquid to water cooled stuffing box.
17. Excessive clearance at bottom of stuffing box between the shaft and casing, causing packing to be forced into pump interior.
18. Dirt or grit in sealing liquid, leading to scoring of shaft or shaft sleeves.
19. Excessive thrust caused by a mechanical failure inside the pump or by the failure of the hydraulic balancing device, if any.
20. Excessive grease or oil in bearing housing or lack of cooling, causing excessive bearing temperature.
21. Lack of lubrication.
22. Improper installation of antifriction bearings (damage during assembly, incorrect assembly of stacked bearings, use of unmatched bearings as a pair, etc.).
23. Dirt getting into bearings.
24. Rusting of bearings due to water getting into housing.
25. Excessive cooling of water cooled bearing resulting in condensation in the bearing housing from moisture in the atmosphere.
26. Wear Ring clearance.

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Guaranteed Energy Saving in Pumps

Today I'll share a very useful sure shot energy saving method in cooling water pumping system. So let me start as usual from some initial questions which are necessary for estimating the amount of efforts required in proving the concept.

How many cooling water pumps do you have in your unit? I have ~50 major such pumps.
What is the total power load of these pumps? It is ~ 6000 kW in my unit - YES whopping 6 MW load.
What is the potential of saving out of this load - May vary from 5 - 7% or more, based on actually achieved savings in my units.

Related References

• Download - Polymer coating boost efficiency
• Method for coating a pump impeller
• Anticorrosion coatings pump up efficiency

How it Works
Whenever a cooling water pump is used it is generally getting corroded over a period of time due to several issues related to cooling water treatment & therefore, mostly it is pitting corrosion which makes the casing inner surface rough & it becomes tough for handling water efficiently.

In a centrifugal pump the action is to provide rotary forces to convert the velocity energy into pressure energy. These centrifugal forces when comes in contact with the rough wall of casing the frictional coefficient between fluid & pump casing wall increases. Thus, overall losses inside the pump increases & hence efficiency drop is observed over a period of time.

When we apply any ceramic or enamel coating on the inside wall of pump casing this frictional resistance reduces, therefore energy saving is achieved. In general I have used this method on different pumps ranging from samll ~100 kW to very large 1 MW pumps & found 5-7% savings actually achieved. The saving range can vary depending on the condition of your pump.

The benefit of this suggestion is that

1. It increase efficiency for new pumps by reducing inherent friction of material & fluid - So you get more efficiency but it will be limited to ~1-2%
2. Increase in efficiency of older pumps - the scope here is more 5-7% or higher
3. Increase in life of older pumps
4. Avoid early damage to new pumps
5. Avoid drop in efficiency of new pumps
6. Delay investment for replacement of older pumps saving capital & interest cost
7. Restore pump head
8. Restore pump capacity

Here are the pics of before & after coating in my unit.




In my case of 50 pumps the estimated investment was only Rs. 20 Lac & saving of 360 kW power @ 6% out of total 6 MW load. This equals to Rs. 114 Lac/year saving at Rs. 4.0 / unit power cost. Thus payback was only 2 months.

Do you still need more good reason to read 'Chemical Professionals'......NO......So get this idea, start working on it, send a proposal to your BOSS..............IT WILL NOT FAIL....................& get a promotion next year.

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Shutdown Learning - Corrosion in Exchangers

In this shutdown, we openend many process exchangers, heaters, coolers etc for inspection and found different types of corrosions.

The most happening incident was in a cooler used as intercooler for ASU compressor. The strange thing was that all the baffles on shell side (cooling water) were gone. There was no indication of there existence except some marks on tube bundle as you can see in larger version of the below image.

Related references

• Galvanic Corrosion - Wiki Reference
• Galvanic Materials in Series - In Waster Service
• Key to Steel
• Download - Anodic Protection - Its Operation & Applications
• Download - Cathodic Anodic Protection

The cooler is an interstage cooler in ASU unit for oxygen compressor. The cooling water flow is on shell side while gas was on tube side. Tubes were of SS & shell including baffles were of CS carbon steel. It seems that heavy corrosion has eaten away all the baffles.



If you can enlarge the photo & see it carefully then you will find marks of existence of those baffles.

Another example of similar type of corrosion is seen in other exchanger. This is a condenser for heavy glycol ether vapors. Cooling water is on tube side. So the corrosion is observed on tube sheet & partition plate.



The opposite side was also no better. In fact the damage is more here.



This is mainly due to electorlytic corrosion induced by presence of salts in cooling water. The easiest way to reduce it is to provide a Zinc Anode so that preferential corrosion or sacrificial corrosion saves your exchanger without much effort. One example is shown below.



These examples indicate that the cooling tower which is supplying cooling water to these exchangers doesn't have proper makeup water & has build up the concentration of salt beyond desired levels.

One should keep in mind that the contact of Zinc on the surface to be protected should be proper. In fact, one should prepare it by buffing or some other means to make it very clean.

Also keep in mind that there should not be any paint or coating on Zinc Anode as it is seen on some points in above image. This defeats the purpose of providing zinc anode. It is an usual thing that when you are in a hurry during shutdown you leave the job on contractor. The labourer does his best by providing coating on Zinc Anode also...............HOW Zzzzz THAT????????

So be careful, sometimes good thing are not so good to do.

Yes as an initial step we provided Zinc anode in these two exchangers.

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