feedwater systems reliability users group (jan 2017) austin, tx...

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Feedwater Systems Reliability Users Group (Jan 2017)

Austin, TX

Stretching NPSHA vs. NPSHR to the Limit

Presenter:

Art Washburn P.E.

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DISCUSSION POINTS• Two Rules to Get You Home and Plant Priorities

• Customer Challenge To Perform Inspections & Maintenance Online

• Manage In-Leakage to Accomplish Inspections by Creative Means

• Sump Pump and System

• NPSHR vs. NPSHA

• Source References

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Two Rules:

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Two Rules:

Rule #1 – Make Conservative Decisions

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Two Rules:


Rule #2 – Maintain Design Control

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Two Rules:



Plant Priorities:

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Two Rules:



Plant Priorities:

1. Nuclear Safety

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Two Rules:



Plant Priorities:

1. Nuclear Safety

2. Legal Requirements

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Two Rules:



Plant Priorities:

1. Nuclear Safety

2. Legal Requirements

3. Efficiency

Customer Challenge to Perform Inspections &

Maintenance Online

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- Inspect Circulating Water Inlet Piping, Safety

Related

- Cross Tie Valve Between Plants Leaks ~750 GPM

- Dual Unit Outage Required to Allow Personnel

Access to Inspect Piping, Water Box Valves

Creative Ideas Needed

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- Site Planning Dual Unit Outage, Estimated Cost

Greater Than $10 Million

- Maintenance Organization Identifies Creative Idea

to Complete Inspections with 750 GPM In-Leakage

- Provide Sump Pump: 1000 GPM @ X FT of Head

Circulating Water Inlet Piping, Water Box, Condenser

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Inlet Circulating Water Piping Access Point,

30” Manway

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Sump Pump Predicted Performance Test Curve

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Net Positive Suction Head Available vs. Required

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Energy acting on the inlet (suction) side of the pump include:

1. Atmospheric Pressure (positive)

2. Lift (negative)

3. Pump Impeller requirements (negative)

4. Friction losses (negative)

In order for the pump to move the water, the Net Positive Suction

Head Available (NPSHA) must be greater than the Net Positive

Suction Head Required (NPSHR).

NPSHA > NPSHR (FT absolute)

Atmospheric Pressure > Lift + Impeller Requirement + Friction

Losses


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The available suction head (NPSHA) comes from atmospheric

pressure acting on the surface of the water.

1 Atmosphere ~ (14.7 PSIA)(2.31 FT/PSI)/(1.0) ~ 33.9 FT abs

NPSHA = 33.9 FT abs

WATER


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The amount of ‘Lift’ is elevation differece between the surface of

the water and the centerline of the pump impeller. ‘Lift’ can be

either ‘positive’ or ‘negative’ depending on the actual

configuration in which the pump is running.

• Sump surface above the pump lift is positive

• Sump surface below the pump lift is negative

WATER

Lift = 20.5 ft


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The pump impeller requirements are a function of the flow rate of

the individual pump. The higher the flow rate, the greater the

NPSH requirement. The NPSH curve the the Oconee Sump

Pump is shown below. At maximum expected flow (1000 GPM),

NPSHR is approximated to be 8.6 FT abs.


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The friction losses in the pipe were an unknown for this pump.

While significant data exists for friction losses in steel pipe,

losses in PVC pipe and fittings is not readily available. Also, due

to the size of the pipe (6 inch) the flow velocities (12 ft/sec) are

much higher than recommended (5 ft/sec).

Based on estimates for friction losses, we knew that we would

be near the limit of NPSH at the 1,000 gpm flow rate. This is

why the actual test was required to determine for certain that the

sump pump would perform as required.


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SUMMARY:

The final equation for NPSH is as follows:

NPSHa > NPSHr

Atmospheric Pressure > Lift + Impeller Requirement + Friction

Losses

33.9 ft > 20.5 ft + 8.6 ft + Friction Losses

33.9 ft > 29.1 ft + Friction Losses

Therefore Friction Losses must be less than 4.8 ft in order for the

pump to perform its intended function.

What we learned in the first test is that the friction losses in the

suction line achieve 4.8 ft when the flow rate goes above

approximately 950 gpm. Therefore, any flow rate below this will

have sufficient NPSH for the pump to perform its intended function.

Test Pit: Maximum Attainable Flowrate at Duplicated

Suction Condition

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Sump Pump: Inadequate NPSHA Performance

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Foot Valve Head Loss Curve: Simmons 8” Valve

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Suction Piping: Friction Losses

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- 6” Sch. 80 Pipe: 1000 GPM, 12.5 FPS, Friction

Loss (7.2 FT / 100 FT)

- 7.2 / 100 = X / 20, X = 1.44 FT

- Limits:

- Steel Pipe, 8 – 12 FPS

- PVC Pipe, 5 FPS max (Wear, Noise)

Discharge Piping: Friction Losses

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- 6” Sch. 80 Pipe: 1000 GPM, 12.5 FPS, Friction Loss

(7.2 FT / 100 FT)

- Unit 3: 7.2 / 100 = X / 500 FT, X = 32.4 FT

- Unit 1: 7.2 / 100 = X / 1100 FT, X = 79.2 FT

- Limits:

- Steel Pipe, 8 – 12 FPS

- PVC Pipe, 5 FPS max (Wear, Noise)

Sump Pump Predicted Performance Test Curve

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Sump Pump Skid Assembly

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Sump Pump Skid Assembly - Finished

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Impeller

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Sump Pump Foot Valve Assembly

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Sized a Vortex Breaker Plate

Plate Diameter Still Fit Thru

30” Access Manway

Added Drain Valve to Allow

Quick Opening from Outside

Pit, Emergent Draining of

Water (250 lbs), and Removal

of Suction Piping System

Valve – Leather Flapper

Suction Piping

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Suction Piping Joints, Fittings, Zero Leakage

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Test Pit: Suction Piping Mock Up of Field Configuration

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Test Pit: Maximum Attainable Flowrate at Duplicated

Suction Condition

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Sump Pump: Inadequate NPSHA Performance

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Field Configuration:

- Suction Pipe

- Fill & Vent Connects

- Manway Cover Positioned

for Installation in an

Emergency

- Limited Access Thru 30”

Manway

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Field Installation: Discharge Piping

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Unit 1: Pump Flowrate Achieved

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Field Installation: 30” Manway Access

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In-Leakage: Dumping Right on Top of Foot Valve

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In-Leakage: View from Turbine Building Bottom Floor

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In-Leakage: Video from Turbine Building Bottom Floor

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Oconee Unit 3: Sump Pump System Configuration

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Oconee Unit 3 Inspections: Sump Pump Performance

Highlights

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- Allowed for Inspections of Circulation Water Piping

- Unwatering Circulating Water Inlet Piping: X Gallons

- Discharge Piping Length of Run: 450 FT

- Capacity: 750 GPM In-Leakage, 900 GPM Maximum

- Discharge Piping 10 FT Sections: Zero Leakage

- 6” Discharge Piping Material: PVC

- Discharge Returned Water Back to Lake Keowee

Oconee Unit 1: Sump Pump System Configuration

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Oconee Unit 1 Inspections: Sump Pump Performance

Highlights

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- Allowed for Inspections of Circulation Water Piping, Water

Box Valves, and an Amertap System Modification

- Unwatering Circulating Water Inlet Piping: 3,542,000 Gallons

- Discharge Piping Length of Run: 1,100 FT

- Capacity: 400 GPM In-Leakage, 880 GPM Maximum Pumped

- Discharge Piping 10 FT Sections: Zero Leakage

- 6” Discharge Piping Material Changed from PVC to

Aluminum.

- Material Change Relieved Fire Watch Requirements, as the

Piping is Routed Thru Operating Units (2 & 3).

- Discharge Returned Water Back to Lake Keowee

- Chemistry Department did not have to Manage 3.5 Million

Gallons of Water Thru Chemical Treatment Ponds

Oconee Unit 1 Inspections: Pump Lost Prime 3 Times

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- Pump Prime was Lost One Time as a Result of Low Water Level

- Water Wave Generating a Vortex

- Scaffold Builder Bumped Dump Valve, Opening Valve

SOURCE REFERENCES:• Centrifugal Pumps: Design & Application, Lobanoff and Ross

(practical application)

• Centrifugal and Axial Flow Pumps, Stepanoff (theory)

• Centrifugal Pumps, Gülich

• Vertical Turbine, Mixed Flow & Propeller Pumps, Dicmus

• Centrifugal Pump Handbook, Sulzer

• Pump Handbook, Karassik

• Centrifugal Pump Clinic, Karassik

• Centrifugal Pumps Selection & Operation, Karassik

• Centrifugal Pumps, Karassik

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Gene Cernan, Last Man on the Moon, Dead at 82 – R.I.P.

THE (HAPPY) END

QUESTIONS ?

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feedwater systems reliability users group (jan 2017) austin, tx...

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