Alignment Rectification after process pipings are connected with Compressor nozzles results in catastrophic failure.

Care must be taken to ensure that alignment readings does not vary during alignment in both the circumstances i.e.
1) when pipe flange is not connected to compressor nozzles
2)when pipe flange is connected with compressor nozzles.
It is good practice to rectify piping and its companion flanges instead of rectifying alignment after piping is connected.This will result in catastrophic failure caused by undue loading and moments on machines casing and other internals.
There should not be load transfer from piping end to machine end after flanges are bolted with compressor nozzle in cold condition.However there may be axial and transverse loading which may occur during actual operation of plant load.This is being taken care during alignment by incorporating  axial and radial values as mentioned in OEM manual

Why maintenance work planning for a confined space entry needs stringent focus or attention ?

  

Let us understand first what is a confined space? Spaces or locations just enough to enter, difficult to enter or exit  and/or not designed for  continuous human occupancy are generally,to my understanding, called confined space.  For example,confined spaces in a process /chemical industry include but are not limited to  tanks, reactors,pressure vessels,columns, volume bottle ,ducts, pipelines, sumps, sewers,  inside culverts and vaults. Confined-space incidents/accidents are  significant cause of workplace death  and injury.  Associated hazards in confined space vary widely; the most common are: oxygen deficiency  presence of flammable materials/ constituents toxic gases or vapors Unless all the above hazards are completely eliminated by taking appropriate  mitigation measures work execution permit shall not be issued.

Whether RCM-single maintenance strategy applicable in all type of industry /organisations in same fashion.?

There is no one fix maintenance strategy which can be applied in all type of industry. To my understanding  maintenance strategy to be adopted successfully to achieve long term reliability depends on following:
1.type of industry(process,continuous,batch production,Hydrocarbon,Engineering
   manufacturing etc)
2.Age of industry.How old industry is?
3. Severity and consequences of failure of assets.(Impact :on assets,human
   being,surrounding/environment and reputation of organisation)

A continuous Process industry like Fertilisers,petrochemical,Oil-gas & Energy sector industry may adopt following Proactive good maintenance Strategy within RCM domain:
- PM :frequency based on past historical data/MTBF/OEM recommendation(capital
  machines)
-PdM or Condition based maintenance to identify failure detection threshold point
  to plan corrective measures to repair the item/equipment proactively before the hard
  failure happens.
-Capital overhaul based on running hours/nos of years/types of cyclic load/service being handled by equipment.

Effect on Rod Load if we increase compressor speed in reciprocating compressor.

To understand the effect of speed on "Rod Load" ,we must know first what is rod load? Actually Rod load is vector sum of Gas load and inertia forces (caused by all reciprocating parts including cross head assembly) acting in the direction of piston rod.The first part i.e.Gas load is function of cylinder chamber pressures and area of piston at crank end and head end.Therefore speed will have no effect on Gas load,however it will have effect on flow rate (capacity) and power absorbed by compressor.The second part i.e. inertia forces is function of mass of reciprocating parts and its acceleration/deceleration.Obviously change in speed will have effect on magnitude of acceleration/deceleration of piston rod assembly during each revolution of the crank.
Hence compressor speed will have effect on "Piston rod load".Its absolute value may increase or decrease depending upon crank angle during each revolution.

How to distinguish between Grinding wheel and Cutting wheel (Cut-off wheel) ?

Some useful tips to distinguish Grinding wheel and Cutting (or Cut-off) wheel are given as below:


1.      Remember: All grinding is cutting operation but all cutting is not grinding operation.

2.      Thumb rule : “THICKNESS”  is the the major difference between cutting and grinding wheels. A newly procured disc or wheel  up to 3 mm(1/8 inch max) thickness  is used as  Cutting wheel. Its radial periphery is utilised for cutting or slotting  operation as it can withstand a great deal of radial stress but not any side stress . Cutting wheel is not designed to take side load. Hence its use as grinding wheel is not recommended.

3.      Grinding wheel or disc start with minimum 6 mm thickness onwards. The shape and thickness of a grinding wheel decide a wheel's type. Grinding wheel can be used for side  as well as radial grinding as per job requirement.

Bellows seals -Material of construction for Thermic fluid application

Selection of  AISI 316Ti  Vs AISI 321 as materials of construction for bellows seals for Thermic fluid application (such as Santhotherm-66, dow therm ,therminol etc) for high temperature application +200 to +300 Degree C)

Generally both the materials are recommended for selection of bellows seals so long maximum temperature is below the creep range.
AISI 321 is Titanium stabilized Austenetic Stainless steel. It is very good corrosion resistant material for high temperature environment where presence of chloride is negligible.Presence of Ti has tendency  to suppress the formation of Chromium carbide under elevated temperature specially at welded construction .Thus depletion of Cr is avoided due to presence of Ti.
But it has less resistance to Pitting-Corrosion as compared to AISI 316 Ti

On the other hand AISI 316 Ti is having 'Mo' in addition to 'Ti:'. Therefore it has very good resistance to Pitting corrosion and has all property of AISI 321.


Obviously AISI 316 Ti shall be comparatively costlier than AISI 321   

Why No-Load Testing is important in Reciprocating compressors after complete overhaul ?

Why No-Load Testing is important in Reciprocating compressors after complete overhaul ?

After complete overhaul (i.e. replacement of worn out bearings -main bearings,conn rod big end bearings,small end bearings,cross head shoe replacements,piston rings and rider rings ,stuffing box pair of rings,etc etc) following should be checked during idle run (no-load ) test for establishing soundness of assembly .
Prior to start up for idle run:
1.Check and ensure that CE (Crank end  or BDC) and Cylinder Head End (TDC) clearances are measured correctly by lead wire and micrometer and values maintained as per OEM recommendation.
2.Check piston rod run out (vertical and horizontal) to ensure correctness of piston and cylinder assembly with respect to slide body or distance pieces wherever applicable.
3.Start auxiliary oil pump and observe that oil is going to all the bearing locations as well as cross head pin and crank shaft main bearings through oil passages .
4. keep barring the crank shaft while oil is flowing to all required locations. Lube oil pressure should not be less than 2.5 kg/cm2 (g).
5.Close all the doors of cross-head guide .
6.Ensure valve and valve covers from cylinders are removed prior to No load Testing.

Observations during No-load Testing

1.Run the compressor for 15 minutes and stop to measure/observe  followings:
  - Temperatures at crank shaft main bearings and intermediate bearings if provided.
  - Temperatures at all conn rod big end bearings and small end bush bearings.
  - Lube oil pressure and Temperature before and after oil cooler.
  - Water temperature at in let and outlet of oil cooler.
  -Temperatures at all cross heads shoes.
  - Piston rod temperatures at stuffing box packing locations.
  - Gear box bearing temperatures
  -Any other abnormality if any.

2. If all the readings in step 1 above are within satisfactory range, run the compressor for next one hour and repeat all those readings mentioned in step 1 above.
3.If all the readings in step 2 above are satisfactory within acceptable range ,run the compressor for next two hours and repeat the readings mentioned in step 1 above..
4 If the readings in step 3 above are within acceptable range run the compressor for next one hour and repeat the readings mentioned in step 1 above.
5. If readings in step 3 and 4 are almost steady ,stop further running. This completes the satisfactory idle run test for minimum 4 hours.In case readings are not steady even after 4 hours of no load  trial , repeating the running further is not advisable rather we should check  for cause of increasing trend of temperature .It could be the misalignment or  poor workmanship which needs attention to be addressed / fixed the problem. After correction , repeat the fresh no load trial as per step 1 to 5 above till the parameters are steady within 4 hours of cumulative running.

Many end users are not following above procedures .They directly start the compressor for load trial .There are two main disadvantages in this case :
1. It may result in catastrophic failure of compressor or bearing seizure because of  possibility of  poor
    workmanship/practices which could have been noticed in first 15 minutes no load trial run.
2.Very fast wear rate of rider rings and piston rings resulting in their low MTBF. As most of the rider rings
   are made of PTFE with graphite filler,during no load a layer of PTFE is formed on sliding surfaces of
   cylinder liners which further reduces the coefficient of friction during load testing or load trial.