Monitoring Submersible motor pump  health for water application

Check points (monitoring points) by pump operator ( Look Listen Feel and Record Approach)

by pump operator:

1. Observe and Record the discharge pressure gauge reading (must have been installed in discharge

piping system).

If the reading is significantly oscillating (hunting to and fro) more than 15-20% of normal

operating point, it gives following signals which can be addressed through skilled service

technicians:

1.1. Strainer might have been choked due to mud /debris/scales accumulation around the

strainer. Needs cleaning of strainer.

2. Abnormal noise coming out from the piping system which is a signal of Cavitation phenomenon

in the system. This may be due to starvation in the pump. Remedy suggested is same as in point

no 1.1 above. OR level of water in underground water tank is lower than strainer location.

Pumps need not to be started unless level in water tank is adequately maintained.

3 Pump is running but with no flow or significantly reduced flow and with shut off pressure ( which

is more than operating pressure):

This indicates that NRV installed in discharge piping system is jammed ( not opening ) .Needs

inspection of NRV.

4.Pump is getting tripped after start of few seconds . This gives signal that

4.1 Either NRV is heavily passing ( WORN OUT FLAPPER ) and discharge valve is in full open

condition. Leading to over load of pump motor . OR

4.2 Pump motor bearing is damaged .

Measurement of motor current will confirm the over loading . This Needs inspection of NRV.

5. Pump is not getting started at all. Following needs to be checked:

5.1 IR value ( Insulation resistance) of wiring of motor. If IR value is less than 0.5 MegaOhm

needs inspection of wire /winding to fix the issue by skilled SERVICE electrician.

5.2 If IR value is within normal limit, still pump is not getting started then it needs inspection of

pump internals for bearing seizure with motor shaft either due to increased clearances or due to

lack of cooling by water as lubricant/coolant. Submersible pump sleeve bearing is water lubricated.

Failure Modes of steam Turbine

 

     The failure modes of steam turbines are classified into following main three categories:

1.         Steam Flow Path parts:   Control valves, Nozzles(HP), Blades (HP), Nozzles (LP), Blades (LP) .
2.         Rotating Parts: Blades (HP), Blades (LP), Rotor, Thrust collar and, Journal Shaft.
3.        Stationary Parts: Casing, Diaphragm, Seals, Thrust and Radial bearings.

       Basic root causes for each damage mode are listed in table below:

Components		Damage Mode	Root Causes
Flow Path Parts	Control Valves	Valve stem Bending Fatigue Failure	High Steam Velocity Fluid excitation
	Nozzles (HP)	Solid Particle erosion Fouling	Hard Foreign Materials inside of pipes
	Blades (HP)	Solid Particle erosion Fouling	Hard Foreign Materials inside of Pipes   Steam Impurity
	Nozzles(LP)	Fouling	Steam Impurity
	Blades(LP)	Drain attack Erosion Fouling	High moisture and High velocity Steam impurity
Rotating Parts	Blades (HP)	High Cycle Fatigue Failure Centrifugal Force Failure	Excessive Excitation Force Excessive Over speed
	Blades(LP)	High Cycle Fatigue Failure Centrifugal Force Failure	Improper water treatment Excessive Over speed
	Rotor	Rubbing and shaft Bow & High Vibration  Disk SCC	Improper start up Drain Intake, Steam Impurity
	Thrust Collar Journal shaft	Rubbing & Scratch or wear	Excessive Thrust Force Improper oil supply
	Bearings	Rubbing and melting	Excessive Thrust Force Improper oil supply
Stationary Parts	Casing	Creep Deformation/Creep Rupture, Erosion and Corrosion	Operation beyond operating widow, Excessive Drain, Galvanic corrosion
	Diaphragm	Diaphragm bending / Deformation , Erosion &Corrosion	Operation beyond operating widow, Excessive Drain, Galvanic corrosion
	Seals	Rubbing and Erosion	Improper startup Excessive Drain

Choice over Reciprocating Compressor and Centrifugal Compressor

Choice depends largely on set of  operating conditions. These conditions range from maximum discharge pressure and temperature to efficiency and cost. The End user must carefully evaluate site conditions of the application before making a choice.

Excerpts are from the paper “What’s correct for my application: A centrifugal or reciprocating compressor” by Paul Gallick of Elliott Company and Greg Phillippi and Benjamin Williams of Ariel Corporation presented at the 2005 Turbomachinery Symposium in Houston, Texas.

Reciprocating and centrifugal compressors of Dresser-Rand

The “typical” reciprocating compressor is used for discharge pressures up to 12,000 psi (828 bar). Special compressors (called hypercompressors) are used in low-density polyethylene production and discharge at pressures up to 50,000 psi (3500 bar). Discharge pressures to 1450 psi (100 bar) for horizontally split centrifugal compressors. Discharge pressures up to 15,000 psi (1034 bar) for radially split (barrel) compressors.

Reciprocating—Can be applied with suction pressures at atmospheric or even a slight vacuum. In vacuum applications, precautions must be taken to prevent atmospheric air from leaking into the cylinder through the piston rod packing. Centrifugal—Inlet pressures to atmospheric or below. For subatmospheric inlet conditions, special seal and buffering designs are employed to keep atmospheric air from being drawn into the compressor.

Maximum Flow • Reciprocating—Reciprocating compressors are positive displacement type compressors. Capacity is limited by cylinder size, the number of throws available, and the available driver speeds. A “throw” is a location on the crankcase where a compressor cylinder can be attached. • Centrifugal—Centrifugal compressors can be sized for an inlet flow of 400,000 acfm (680,000 m3/hr) in a single body. The maximum flow through a centrifugal compressor is limited by the choke point, which is the point at which the flow through some part of the compressor nears a velocity of Mach 1.

Minimum Flow • Reciprocating—Similar to the maximum flow, the minimum flow in a reciprocating compressor is limited by cylinder size, stroke, and speed. Very small reciprocating compressors are available. • Centrifugal—Centrifugal compressors can be sized for flow as low as a few hundred acfm. Unlike a reciprocating compressor where minimum flow is solely a function of compressor geometry and speed, the minimum flow for a centrifugal compressor is limited by an aerodynamic condition known as surge, which is a function of compressor geometry, speed, aerodynamic gas conditions, and system resistance.

Flow Range • Reciprocating—Reciprocating compressors have the ability to change flow (throughput) through speed control, the addition of fixed clearance to a cylinder (fixed or variable volume clearance pockets), cylinder end deactivation, and system recycle. Typical flow range might be 100 percent down to as low as 20 percent, and even lower.

Compressed Gas Molecular Weight • Reciprocating—A reciprocating compressor has no limit with regard to molecular weight. Very light and very heavy gases are compressed equally well. Over the range of molecular weight different application configurations may be required. For example, very low molecular weight gases may present some seal challenges and very high molecular weight gases pose issues with efficiency. But nonetheless, the recip handles the whole range quite well. • Centrifugal—Compression ratio is highly dependent on molecular weight. Head is developed by increasing gas velocity to create kinetic energy and then converting the kinetic energy to pressure in the diffuser. The amount of kinetic energy is a function of gas velocity and mass or molecular weight. Centrifugal compressors are used for a broad range of molecular weight including low molecular weight applications such as hydrogen recycle and high molecular weight applications using refrigerant gases with molecular weights over 100.

Compression Ratio • Reciprocating—The maximum compression ratio that a reciprocating can handle in one stage is limited mostly by compressed gas discharge temperature. The piston rod load generated by the compression ratio may also be a limit. Typical compression ratios are 1.2 to 4.0. • Centrifugal—Compression ratio is a function of gas molecular weight,compressibility,stage geometry,compressor speed,and the number of compressor stages. For a specific gas, the limits to compression ratio are the mechanical and rotordynamic limitations on speed and the number of stages that can be accommodated in a single body. Discharge temperatures resulting from high compression ratios can usually be controlled by intercooling.

Efficiency • Reciprocating—Reciprocating compressors have a very characteristic adiabatic efficiency curve (Figure 8). As compression ratio drops, adiabatic efficiency drops. Efficiency changes with molecular weight. Efficiency will also vary with several other factors, most significantly the compressor cylinder’s ratio of valve flow area to main bore diameter and piston speed.

Reciprocating Compressor Efficiency. • Centrifugal—Polytropic efficiency is typically used for centrifugal compressors rather than adiabatic. Adiabatic is commonly used for air compressors. Typical polytropic efficiencies range from 70 percent to 85 percent. Efficiencies approaching 90 percent are possible. In a centrifugal compressor, efficiency is primarily affected by the internal leakage and mechanical losses.

Cost: Capital and Operating • Reciprocating—Generally a reciprocating compressor will have a lower capital cost since centrifugals use complex geometry parts but recips have a higher operating cost compared to a centrifugal. A centrifugal compressor has fewer wearing parts, resulting in lower operating costs in terms of replacement parts, repairs, and downtime.

Safety hazards of hot work in running hydrocarbon processing plants

Hot work (Cutting ,Grinding,welding )  in running process plants needs stringent safety risk assessment and adequate risk mitigation plan compared to non process geographical location in an organization.
How to ensure Zero safety risk in process plants ?

1.Ensure proper barrication all around the hot work location with high temperature resistant materials/blankets in a manner that no weld splatters or hot materials come out from the barrication.
2.Ensure breathing opening at one of diagonal top corner opposite to hot work location in form of chimney of suitable height . This is required for ease of welder /grinder doing work.If the hot job is being done at pipe rack area,ensure there is no unsafe conditions just below the work location.Remove oily waste/plastics waste if any .
3.If grinding work is performed ,ensure that  maximum allowable grinding wheel speed (RPM) is always more than grinding machine RPM.
4.Check the direction of rotation of grinding wheel.Ensure that position of grinder is such that hot spatters does not spread or fly due to centrifugal force  towards the chimney side.
5. Ensure zero- LEL near by work location continuously.
6.Job should be executed by competent personnel only.

Cost of Non- Compliance

Statutory and legal Compliance not only ensure a safe working environment but it enhances the morale of the persons working in the organization.High morale of employees and contractor's crew members improves the productivity, profitability and image of the organization.
Statutory and legal compliance plan must become an integral part of organizational plan and reflect the evolution of industry.
Cost of Non-Compliance shall be significantly high and it will impact adversely the profitability and reputation of organization. 

Prevent breaking of FRP blades of Cooling Tower fans of process industries or power plants during start up.

Important checks during Preventive Maintenance Program of Cooling Tower Fans to prevent breaking of FRP blades of Cooling Tower fans during start up.

Ensure that  annual CT fan PM check list contain following points also in addition to all other points which maintenance engineers are following in their work place. Any abnormality must be thoroughly examined and necessary repair /maintenance if required shall be carried out to ensure the reliability till the next annual PM opportunity:

1.Inspect for any loose or missing bolts in the fan shaft bushing,the fan hub, and the fan shaft bearing(s).

2. Check the fan blades for looseness, first by twisting the blade

by hand, and then by moving the blade tip up and down. There should be no play or slippage.

3. Inspect each blade for excessive scale build-up that could cause vibration.On FRP blades, consider cleaning the blades and applying a coating of

UV inhibiting paint if the blades are showing signs of UV attack/deterioration. 

4.Carefully check the aerodynamic fan blades surfaces ,shanks/shrouds thoroughly for any cracks or damage or severe pits which may become potential reason for breaking of FRP blades during start up.In case of severe pits,replace blades.

5. Ensure that any weep holes in the end of the blades are open and clear.

This is a must so that water does not accumulate in the hollow blade of fans

causing fan imbalance.

6..Check blade track to be sure all blades are running in the same plane.

7..Check individual fan blade pitch to be sure all blades are pitched at the same

angle.If uncertain, measure the pitch with an inclinometer.Check torque on all fan blade clamp bolts. Record pitch angle in your records.

8.Confirm the fan seal disc is in place and all attaching bolts are properly torqued.

9. Confirm the fan tip clearance to the fan stack is uniform around the fan stack.

Clearances are within the design value. Adjust fan stack to proper clearance.

10. Rotation: Turn the fan by hand to ensure that it moves freely with

no rough spots, binding, or other malfunctions that could cause

vibration or fan motor overload. While rotating the fan, check the

blade tracking. 

11. Direction of Rotation: On initial start-up, or if the fan motor has

been rewired, bump the fan motor and note the direction of

rotation. It should rotate in the direction indicated by the arrow on

the fan cowl.

12. Operation: On initial start-up, run the fan in the manual position for

several minutes and check for any unusual noises or vibration.

Concept of Liquid cavitation - A better understanding about boiling,flashing and cavitation

Concept of Liquid cavitation:

Cavities in the liquid body is the result of partial vaporization of liquid. Although the term cavitation can
mean the formation of cavities of gas or vapor in a liquid, the cavitation process consists of both liquid cavity formation, and liquid cavity deformation. It is therefore a reversible, double change of state phenomenon. On the hand the terms boiling and flashing are special categories of vaporization. Boiling is defined as the specific vaporization point of a liquid in the presence of local atmospheric pressure .
Flashing involves a fluid’s rapid phase change from liquid to vapor without the return of the fluid to the liquid phase.
One should not mean that cavitation, boiling,and flashing all are the same thing and therefore can be used interchangeably.

There are also occurrences in which relative flow arrangement, entrainment/dissolution, or chemical reaction can lead to cavity formation and later collapse in what is known as pseudo-cavitation. Liquids exposed to air or other gases can absorb a portion of that gas. Liquids often therefore become a solution of the parent liquid and a dissolved gas, with a different vapor pressure from that of the pure liquid. The mixture of liquid and vapor is now a compressible fluid.  When pressure increases, the mixture passes through its vapor pressure level and the vapor pockets instantly collapse like tiny balloons. Dissolved air or gases coming out of solution and imploding has been referred to as pseudo-cavitation.

It is general belief that Cavitation is always problematic and detrimental and therefore always should be eliminated or at least minimized. This belief is absolutely correct in perspective of process equipments of process industry. But there are some application such as subsurface drilling operation or process mixing applications where the associated turbulence is advantageous. A recent development in mixing micro technology called cavitation micro streaming, whereby a gas bubble inside a liquid is made to oscillate at a various frequencies, greatly enhances the mixing of blood samples with reagents.
The process of cavitation begins when the pressure on portions of the liquid decrease to a point low
enough for the fluid to change states, from a liquid to a gas. This occurs at the vapor pressure of the
liquid.