Criticality Analysis – Assessing Vulnerability: The Important Pipes Below

Joe Foote, PE PNWS AWWA Kennewick WA May 2017

Contents • Overview/Purpose of

Criticality Analysis

• Criticality Analysis • Facility • Pipe • Valve

• Summary

Purpose of Criticality Analysis • Consequences of failure

• Strength of the system with components off-line • Impacts to pressure and supply • Distribution network redundancy

• Valve criticality and isolation

• Prioritization of identified projects

• Supply and boosting facility “firm” capacity

Two-part Approach • Mass balance

• Source • Pump station • Storage

• Hydraulic modeling • Pipe Criticality: Strength of the pipeline network • Valve Criticality: Availability of valves to isolate breaks, or failed valves

Mass Balance Approach

Part of master planning • Supply redundancy

• Pump station redundancy

• Availability of storage

Hydraulic Model Approach - Pipelines Pipe Criticality – the importance of any single pipe segment in the network

• Closes each pipe in the system and evaluates the results • Finds “Functional” dead-ends, needed looping • Needed tie-ins • Service to critical customers

Hydraulic Model Approach - Valves

Valve Criticality • Evaluates consequences if a

valve fails to close • Isolates each valve in the

system and reports number of valves required, demand isolated

• Indicates difficulty of isolating a valve in the field

Criticality Process – Criticality Goals

Identify level of desired resiliency • Extent of evaluation

• Single component • Entire facility • Analysis of dead-ends

• Context of decisions • Age of facilities • Capital project prioritization • Operational flexibility

Redundancy

Cost

Criticality Process – Hydraulic Criteria • Develop hydraulic performance criteria

• Identify the target demand scenario(s) • Average day, Maximum day, Peak hour • Fire flow

• Pressure criteria • 20 to 30 psi

• Extent of pressure drop or disconnection • Pressure loss: Service pressure drops below criteria limits • Disconnection: The pipeline that has no looping

• Number of customers impacted • Amount of demand

Criticality Process – Valve Criteria • Number of valves required to isolate a failed valve

• Valve on distribution main • Valve on transmission main

• Demand isolated by valve closure

• Impact of critical customer to isolate failed valve

Software Tools • Protector and VCM extension - Innovyze • WaterCAD/WaterGEMS - Bently • OptiCritical - Optimatics

• EPA Net-based

• Data intensive • Data requirements for hydraulic models

• Calibrated GIS based model • GIS data for the location of system valves • GIS data for the location of critical customers

• Data streamlining • Skeletonizing or phased analysis

Model Development • Develop a GIS based

calibrated hydraulic model

• Skeletonize the model (as required)

• Validate the skeletonized model (as required)

• Create criticality scenarios

Streamline Data

40,000 pipes

8,000 pipes

Criticality Modeling – Pipes • Define location of critical customers

• Locate simple dead ends

• Group results • Categorize: disconnection or low pressure • Group pipe segments in series

• Rank the importance of critical pipe groups

• Validate project criticality with full model

Pipe Criticality Results Disconnection

Pipeline Criticality Scoring Maximum Pressure Violation – worst case pressure loss

Scoring Basis Critical Pressure Loss Pipeline Disconnection Pipeline

Critical Customer Score (number of critical customers with criteria violation)

10 points per critical customer, multiplied by the pressure violation

10 points per critical customer

General Customer Score (customers with criteria violation)

1 point per 100 equivalent people, multiplied by pressure violation score

1 point per 100 equivalent people

Pressure Violation Score (Magnitude of pressure loss)

1 point per 10 psi pressure violation, round up as long as the pressure violation is 10 psi or greater

N/A

Ranked Critical Pipes

• Prioritization of any existing improvement

• Development of improvements

Rank Projects

• Critical Customer Score = 10 points per critical customer below criteria pressure multiplied by the pressure violation

• General Customer Score = 1 point per 100 customers, multiplied by the pressure violation score

• Pressure Violation Score = 1 point per 10 psi below criteria, round up if over 10 psi

• Total Score = Critical Customer Score + General Customer Score + Pressure Violation Score

Group ID

Max Pressure Violation

Pressure Violation

Score

Critical Customers

Equivalent People

Customer Score

Total Score Rank

NH4A 40 4 - 8,990 360 364 1

NH51 5 0 5 2,217 250 250 2

H27B 21 3 - 3,579 107 110 3

NH86 19 2 - 1,235 25 27 4

L500 24 3 - 410 12 15 5

T33A 14 2 - 544 11 13 6

NT52 10 1 - 97 1 2 7

Secondary Prioritization • Secondary ranking criteria

• Areas with limited capacity • Headloss (2ft/1000 ft, 6ft/1000 ft) • Velocity 5ft/sec

• Age/Material • Identified growth areas

• Hydraulic capacity results may inform the improvement alternative process

Criticality Modeling – Valves • Skeletonized model (as required)

• GIS valves • Spatially located on model pipes • Relocate valves on junctions

• Run valve criticality

Red and yellow valves are required to isolate the black and yellow valve

Valve Criticality • Valves that require a large

number of other valves to isolate

• Valves that would impact critical customers

• Valves that impact large customer demand

• The addition of a few valves may reduce the criticality of many valves

Valve Criticality Results

• Transmission: Red valves require 11 or more valves to isolate

• Distribution: Yellow valves require 7 or more to isolate

Critical Valve Information • Operational Value

• Resource requirements • Prioritize valve maintenance

program • Identifying system improvements

• Limitations • Complexity based on size of

system • Limited tools for operator

reference

Summary • Mass balance

• Critical pipes • Pressure loss • Disconnection • Prioritization

• Valve criticality • Valves to isolate

(manpower) • Projects, maintenance

priority

A Special Thanks to • City of Spokane

• Dawn Wirz, Murraysmith

Questions?

Contact: Joe Foote, PE

Murraysmith

M: 421 W Riverside Ave, Suite 762

Spokane, Washington 99201

P: 509.321.0340

E: Joe.Foote@murraysmith.us