BIBE_Pipesonic_Report_Oak_Springs_Fill_Line_2024_07_31_0004.pdf

Post Inspection Activity Summary for the condition assessment of the Oak Springs to Chisos Basin water fill line at Big Bend National Park per BIBE 317515 – 3.1.1

2024-07-31

Report: Harrison Richarz and Tuukka Vӓlimaa, M.Sc.

Quality Assurance: Dr. Werner Richarz, PhD, P.Eng. FASA

DISCLAIMER

All forms of non-destructive testing involve an intrinsic level of uncertainty.

As non-destructive testing requires accurate input parameters, outputs are affected by variation from assumed parameters.

The results given in this document are based on PipeSonic’s prior knowledge, experience, and understanding of the client’s particular requirements, input values provided by the client, and parameters measured by PipeSonic, each with its own inherent levels of uncertainty. Results also indicate the values for the date on which measurements were taken in the field and do not predict future values.

PipeSonic acknowledges that the client may use this report to consider potential opportunities for pipeline replacement/rehabilitation; however, PipeSonic disclaims any liability that may arise in connection with decisions based on these results or any suggestions or recommendations arising from them made by another party.

COPYRIGHT STATEMENT

This document is Copyright © 2024 PipeSonic USA Inc., All Rights Reserved.

EXECUTIVE SUMMARY

• Most exposed pipes showed little external corrosion.

• PII analysis shows that the thinnest portions of the pipe still retain over 80% of their original wall thickness, with an average value of 86% or twice the minimum required thickness for the entire run of pipe.

• The 2001 repair clamp appears visually to be in almost identical condition as when photographed in 2002 and 2022.

• Ultrasonic measurements agree with prior measurements with an average of 94% of the original wall estimated to be remaining.

• No active leaks greater than 1 gal/min were detected on site.

• Given the pipes’ present condition, break history, with minimal external engineering work another inspection would not be recommended for another 5-7 years.

• While analysis is ongoing, no segments yet display a risk of near-term failure.

• The exposed section of pipe located at 29°16'41.10"N 103°19'31.92"W should be cleaned, coating and encased in concrete (as it is downstream):

• Those sections located in the drainage ditch, or which are in areas where they are subject to foot traffic (approximately 400-450 ft total) could benefit from an epoxy coating, and where practicable, some form of encapsulation to prevent further surface erosion.

TABLE OF CONTENTS

Disclaimer

Copyright Statement

Executive Summary

Table of Figures

Table of Tables

Introduction

Technology Description

Site Description

Site Map – Exposed sections in pink

Mobilization Summary

Inspection activites

Fill Line Contstruction

Minimum wall thickness

Reinterpretation of past results

Leak Detection

Acoustic wall-thickness estimation

2023 Ultasonic measuments

Detailed Pipe-wall condition assessment Results

Remaining Service Life / End of Economic Service

Detailed condition assessment results

Segment 1

Segment 2

Segment 3

Segment 4

Segment 5

Segment 6

Segment 7

Segment 8

Segment 9

TABLE OF FIGURES

Segment 10

Segment 11

Segment 12

Segment 13

Segment 14

Segment 15

Segment 16

Segment 17

Segment 18

Segment 19

Segment 20

Segment 21

Exposed pipe segments

Summary & Recomendations

Appendix 1: leak detection via correlation

Appendix 3: potential remediation sites for exposed pipe

Appendix 4: Inspection images

TABLE OF FIGURES

Figure 1: SCADA display

Figure 2: Pipe-tee at blow-off valve

Figure 3: Pipe serries marking on exposed pipe

Figure 4: Manufacturer’s specifications

Figure 5: Manufacturer’s specifications

Figure 6: Comparison of probability distribution of thickness in 2022 and 2024

Figure 7: Ultrasonic testing at P20 (29°16'31.29"N, 103°19'12.04"W)

Figure 8: PII Test Segment Map

Figure 9: P7 (29°16'57.26"N, 103°19'56.24"W)

Figure 10:P28 (29°16'12.18"N, 103°18'15.25"W)

Figure 11: Estimated end of safe operating life for S15

TABLE OF TABLES

Figure 12: Testing at P1 29°16'54.94"N, 103°20'14.48"W)

Figure 13 P2 (29°16'55.40"N, 103°20'10.99"W)

Figure 14: Inlet at treatment plant

Figure 15: Leak detection arrangement

Figure 16: P15 (29°16'43.15"N, 103°19'30.34"W)

Figure 17: P17 (29°16'37.42"N, 103°19'26.87"W)

Figure 18: P31 (29°16'5.04"N, 103°18'10.83"W)

Figure 19: P16 (29°16'41.14"N, 103°19'31.93"W)

Figure 20: P16 (29°16'41.14"N, 103°19'31.93"W)

Figure 21: P16 (29°16'41.14"N, 103°19'31.93"W)

Figure 22: Exposed pipe (29°16'42.81"N,103°19'30.28"W)

Figure 23: P10 (29°16'54.91"N, 103°19'46.24"W)

Figure 24: P11 (29°16'52.58"N, 103°19'46.69"W)\

TABLE OF TABLES

Table 1: Comparison of ultrasonic thickness measurements

Table 2: Summary of wall thickness measurements 2002

Table 3: Summary of wall thickness measurements 2022

Table 4: Summary of wall thickness measurements 2024

Table 5: Summary of PII wall thickness measurements

Table 6: Comparison of minimum wall thickness and annual wall loss rates

Table 7: Remaining surface life at constant wall loss

Table 8: Estimated remaining min,wall thickness 2024/50

Table 9: Air Release Valve Images

Table 10: Oak Spring pump house interior images

Table 11: Blow-off valve (29°16'44.43"N, 103°19'38.40"W)

Table 12: Repair clamp (29°16'51.83"N, 103°19'46.11"W)

Table 13: P12 ( 29°16'50.64"N, 103°19'44.78"W

Table 14: Distressed Pipe (29°16'41.10"N, 103°19'31.92"W)

Table 15 P22 (29°16'31.65"N, 103°18'59.35"W)

Table 16: Various Test Points

TABLE OF TABLES

Table 17: Exposed pipe at trail head (P30, 29°16'9.07"N, 103°18'12.85"W)

Table 18: Exposed Pipe ( 29°16'7.57"N, 103°18'12.28"W)

Table 19 Exposed Pipe (29°16'7.57"N, 103°18'12.28"W)

Table 20: Exposed Pipe (29°16'50.78"N, 103°19'45.21"W)

Table 21: P19 (29°16'32.15"N, 103°19'15.71"W)

Table 22: Exposed Pipe (29°16'52.02"N, 103°19'46.30"W)

Table 23 Exposed pipe (29°16'51.35"N, 103°19'45.59"W)

Table 24: Exposed Pipe ( 29°16'53.15"N, 103°19'46.47"W)

Table 25: Exposed pipe (29°16'52.59"N, 103°19'46.68"W)

Table 26 P31 (P31 (29°16'5.04"N, 103°18'10.83"W)

INTRODUCTION

INTRODUCTION

The National Parks Service has issued BIBE 317515 which covers the Rehabilitation of the Chisos Basin

Water System at Bing Bend National Park in Texas. Section 3.1.1 of that document outlines the need to conduct a condition assessment of a 3 mile, 3.5" 1950’s galvanized steel feeder line. PipeSonic will inspect the line using its proprietary non-invasive Pipe Integrity Inspector (PII) technology to establish the current condition(s) of the pipeline, estimate the rate of pipe degradation by comparison to the two previous tests

(2022 and 2002) and estimate the remaining service life of the pipeline under the current operating conditions.

TECHNOLOGY DESCRIPTION

Pipe Integrity Inspection (PII) analyzes the evolution of controlled acoustic signals as they pass through a water main, relating the dynamic sound fields generated by our sound source to changes in pipe wall conditions such as thickness, strength, and tuberculation down to the stick. The PII field kit is entirely non-invasive and built around a conventional correlator, which attaches accelerometers or hydrophones to hydrants, valves, or exposed pipes. PII uses a modified line-locating pulse generator, which creates a small controlled “pulse” in the water column by gently vibrating the surface of the pipe. An ultrasonic thickness gauge verifies pipe wall thickness locally.

SITE DESCRIPTION

A 3 ½” galvanized steel pipe supplies water from the Oak Spring pumping station to the Chisos Basin Water

Plant at the Big Bend National Park. Installed in 1955, the line is composed of individual 20-foot threaded pipe segments mechanically jointed together over a twisting, mountainous route. Approximately 20% of the pipe is exposed to the elements. During the inspection the pipe registered a maximum pressure of 708 psi.

Figure 1: SCADA display.

SITE MAP – EXPOSED SECTIONS IN PINK

SITE MAP – EXPOSED SECTIONS IN PINK

MOBILIZATION SUMMARY

MOBILIZATION SUMMARY

PipeSonic mobilized 2 team members to Big Bend who were onsite from January 17th through to the 21st.

They were accompanied by two operators from Operational Technical Services (OTS) from California and by several volunteers from the National Park Service. While mobilizing to one of the inspection sites, a leak was discovered near the group campground washrooms, of which NPS was already aware.

A GIS survey by Doucet/Kleinfelder was used to guide the team members to the site. For the most part, the survey appeared accurate as to the location of the pipe, however the pipe depth indicated in the initial survey was in most cases shallower than when excavated, sometimes by a foot or more.

INSPECTION ACTIVITES

Pipe Sonic accessed the pipe surface at 35 points, 17 of which were excavated by PipeSonic and subsequently restored. The remaining 18 were already exposed, some on the hiking paths. Ultrasonic thickness testing confirmed that the pipe wall at the exposed sections has an apparent average wall thickness between .189 and .238 inches ±2.5%. With two exceptions, little evidence of surface corrosion was observed. What at first blush appeared to be rust, could usually be removed by a dry paint brush or wet wipe to reveal an un-pitted pipe surface.

It was not possible to locate the pipe at three of the planned locations, (P29, P28, and P27) even with the aid of a Schonstedt MAGGIE Magnetic Locator. PipeSonic has updated the GIS map to reflect the actual measurement points as well as the pipe depth for those locations where this differed from the information provided1. It was also discovered that in some locations it was possible to extend the distance between inspection points, allowing for two or three planned segments to be combined into a single segment for more rapid testing. Two ground propagation tests were conducted in the vicinity of point 30 and the revised point

29 which was judged to have the most representative soil for the sections of pipe not buried in rock.

FILL LINE CONTSTRUCTION

During the inspection, and through subsequent investigations by NPS staff, several markings were discovered on the pipe. The markings indicate that pipe tees and reducers are galvanized malleable iron, while the pipe body is galvanized steel. Referencing the manufacturer’s catalogues for 1949 and 1952, 1 https://www.dropbox.com/scl/fi/tlrcybp70wdf3udujb5z8/8999-003-Water-Line-Grid-Corrected- Depths.kmz?rlkey=t0ms3jp76zzv1uea1ddw0vd2g&st=m4qt05np&dl=0

FILL LINE CONTSTRUCTION

PipeSonic was able to ascertain the original construction specifications which differ substantially from the assumptions used in the 2002 and 2022 inspections.

Figure 2: Pipe-tee at blow-off valve.

Figure 3: Pipe serries marking on exposed pipe.

For example, the original wall thickness in both reports was estimated at 0.25", as compared to the manufacturer’s specification of 0.226". This led both reports to overstate the total volume of wall lost.

Similarly, both reports used a lower value for the pipe’s yield strength: 30,000 psi in 2022 and 35,000 psi in

2002; whereas Crane reports a minimum yield strength of 45,000 which is a difference of about a third.

Crane’s catalogue states their steel has an average ultimate tensile strength of 76,000 psi while the prior reports used a value of 48,000 as both had assumed the pipe was made of a lower grade of steel.

Figure 4: Manufacturer’s specifications.

Figure 5: Manufacturer’s specifications.

It is also worth mentioning that the fittings and pipe appear to be from wartime stock as the Crane catalogue indicates that the “heavy” stamping was discontinued prior to 19482.

2 See Crane catalogue 1949 pg. 148 and 1955 pg. 146

MINIMUM WALL THICKNESS

AWWA M11 provides the standard method for calculating the minimum wall thickness required for a steel pipe to resist a specified internal pressure3:

ℎ =

𝑃𝐷𝑂

2𝑠

Where:

ℎ = minimum specified wall thickness in inches 𝑃 = operating or surge pressure in pounds-per-square-inch 𝐷𝑂 = pipe outside diameter in inches 𝑆= allowable stress in pounds-per-square-inch

Per AWWA M11 𝑆 is typically replaced by a value equal to 50% of the steel specified minimum yield strength (SMYS) to provide a factor of safety of two.4 The surge pressure is typically defined as 100 psi more than operating pressure.

Using the information measured onsite and from the manufacturer’s catalogue the following values can be used to compute the minimum wall thickness required for the Oak Sprin fill line:

𝑃𝑤𝑜𝑟𝑘𝑖𝑛𝑔 = 708 psi

𝑃𝑠𝑢𝑟𝑔𝑒 = 808 psi

𝐷𝑂 = 4 inches 𝑆= 45,000 psi

Giving the following values:

Working Pressure minimum wall thickness:

ℎ = 708 × 4

2 (45000 × 2)

= 0.063"

Surge pressure minimum wall thickness:

ℎ = 808 × 4

2 (45000 × 2)

= 0.072"

As watermains are typically designed to incorporate both a factor of safety of 2 and the manufacturer’s casting tolerance, in this case ± 12.5%, the value of ℎ must be multiplied by 1.25 to obtain the minimum allowable wall thickness or ℎ𝑚𝑖𝑛. Using the “worst case” surge scenario one thus obtains:

ℎ𝑚𝑖𝑛 = 0.072" × 1.25 = 0.089"

This value for ℎ𝑚𝑖𝑛 is .035" less than the 0.124" value calculated by Stantec in 2022 as they used an allowable stress of 30,000 psi. The revised calculations point to a longer potential service life for the fill line.

3 AWWA M11, pg. 37 4 AWWA M11 pg. 38

REINTERPRETATION OF PAST RESULTS

Based on the information obtained about the pipe’s original construction it is possible to recontextualize the results of the 2002 and 2022 ultrasound thickness measurement. In short, the annualize rate of wall loss is reduced by a factor of 4 as compared o the analysis conducted previously.

Table 1: Comparison of ultrasonic thickness measurements

Table 2: Summary of wall thickness measurements 2002 min max avg min max avg 1955 0.198 0.254 0.226 - - - 2002 0.196 0.284 0.239 87% 126% 106% 2022 0.187 0.263 0.222 83% 116% 98% 2024 0.189 0.238 0.212 84% 105% 94%

% original average valueYear Wall thickness (inches) min max avg min max avg max avg 0+00 0.198 0.254 0.226 0.229 0.242 0.235 4.0% 0.0000 0.0000 6+50 0.198 0.254 0.226 0.216 0.26 0.242 7.1% 0.1481 0.0000 9+40 0.198 0.254 0.226 0.23 0.254 0.242 7.1% 0.0000 0.0000

20+00 0.198 0.254 0.226 0.216 0.252 0.234 3.5% 0.1481 0.0000 68+00 0.198 0.254 0.226 0.203 0.254 0.239 5.8% 0.3407 0.0000 69+00 0.198 0.254 0.226 0.239 0.284 0.253 11.9% 0.0000 0.0000 71+80 0.198 0.254 0.226 0.196 0.277 0.243 7.5% 0.4444 0.0000 71+90 0.198 0.254 0.226 0.226 0.265 0.247 9.3% 0.0000 0.0000 91+30 0.198 0.254 0.226 0.214 0.25 0.23 1.8% 0.1778 0.0000 91+50 0.198 0.254 0.226 0.212 0.248 0.237 4.9% 0.2074 0.0000 94+25 0.198 0.254 0.226 0.206 0.254 0.23 1.8% 0.2963 0.0000 96+65 0.198 0.254 0.226 0.228 - 0.236 4.4% 0.0000 0.0000 108+00 0.198 0.254 0.226 0.22 0.251 0.2355 4.2% 0.0889 0.0000 114+70 0.198 0.254 0.226 0.229 - 0.24 6.2% 0.0000 0.0000 115+30 0.198 0.254 0.226 0.225 0.239 0.245 8.4% 0.0148 0.0000 148+30 0.198 0.254 0.226 0.199 0.277 0.24 6.2% 0.4000 0.0000

Location Wall thickness (inches)

Δ Annual Loss Rate (mil/yr.)1955 2002

Table 3: Summary of wall thickness measurements 2022

Some of the differences between the 2002, 2022, and 2024 may be explained by the default velocities for the three different ultrasonic thickness gauges the Olympus 38DL PLUS used in 2022 has a default speed of sound of 5,850 m/s while the Wintac WT100A used in 2024 uses 5,900 m/s and according to the manual for the now discontinued Panametrics 26DL Plus its default setting would have been 5,890 m/s.

By way of comparison, at 5,850 m/s it took the sound 1.624 µs to travel the 0.187" minimum thickness measured by the Olympus unit, while the test signal took 1.627 µs to travel the 0.189" minimum thickness measured by the Wintac, a difference of 0.2%.

Comparing the probability distribution of thickness from the previous tests with PipeSonic’s measurements in 2024 we see that the shape is extremely similar.

min max avg min max avg max avg 1 0.198 0.254 0.226 0.193 0.23 0.215 5.0% 0.489 0.168 2 0.198 0.254 0.226 0.196 0.237 0.219 3.3% 0.444 0.110 3 0.198 0.254 0.226 0.187 0.239 0.217 4.1% 0.578 0.137 4 0.198 0.254 0.226 0.201 0.239 0.220 2.6% 0.370 0.088 5 0.198 0.254 0.226 0.206 0.227 0.215 5.0% 0.296 0.168 6 0.198 0.254 0.226 0.193 0.237 0.222 1.9% 0.489 0.064

7A 0.198 0.254 0.226 0.21 0.236 0.223 1.4% 0.237 0.048 7B 0.198 0.254 0.226 0.211 0.238 0.222 1.9% 0.222 0.064 8 0.198 0.254 0.226 0.21 0.238 0.229 1.2% 0.237 0.000 9 0.198 0.254 0.226 0.198 0.234 0.216 4.2% 0.415 0.141 10 0.198 0.254 0.226 0.211 0.233 0.223 1.1% 0.222 0.037 11 0.198 0.254 0.226 0.203 0.236 0.219 3.1% 0.341 0.105 12 0.198 0.254 0.226 0.22 0.263 0.233 3.0% 0.089 0.000 13 0.198 0.254 0.226 0.211 0.237 0.226 0.2% 0.222 0.006 14 0.198 0.254 0.226 0.204 0.228 0.217 3.9% 0.326 0.132 15 0.198 0.254 0.226 0.211 0.233 0.221 2.0% 0.222 0.068 16 0.198 0.254 0.226 0.212 0.236 0.228 0.7% 0.207 0.000 17 0.198 0.254 0.226 0.215 0.239 0.229 1.2% 0.163 0.000 18 0.198 0.254 0.226 0.211 0.239 0.224 0.9% 0.222 0.030 E1 0.198 0.254 0.226 0.195 0.241 0.225 0.3% 0.459 0.010

Location Wall thickness (inches)

1955 2022 Δ Annual

Loss Rate

LEAK DETECTION

Figure 6: Comparison of probability distribution of thickness in 2022 and 2024

LEAK DETECTION

A Gutermann Aquascan 650 leak detection correlator was used to check for leaks along all segments. For these surveys no external noise was created while the instrument “listened” for leak sounds which would be detected by both sensors and interpreted by the instrument as similar sounds delayed in time. Appendix 1 provides more information on leak detection via cross-correlations. Even with the detection threshold set to maximum sensitivity no leaks were detected in real time on site. The recorded sensor signals were remotely post-processed by PipeSonic applying signal specific noise filtering to lower the detection threshold bellow 1 gal/min, however no such leaks have been confirmed in the segments analyzed.

ACOUSTIC WALL-THICKNESS ESTIMATION

ℎ = 𝜌𝑜𝑐𝑜

𝐷

𝐸

1 − 𝑣2 𝑐𝑜 𝑐𝑤 2 − 1

Where:

ℎ = average wall thickness 𝜌𝑜 = density of water 𝑐𝑜 = speed of the sound in the open channel 𝑐𝑤 = speed of sound in the pipe wall 𝑣 = Poisson’s ratio for the pipe wall 𝐷 = outside diameter of the pipe 𝐸 = Young’s modulus of the pipe wall

Using the manufacturer’s specifications and typical values for the density of water and the speed we can solve for 𝑐𝑤 of the original pipe which comes to 4,341 ft/s.

2023 ULTASONIC MEASUMENTS

2023 ULTASONIC MEASUMENTS

PipeSonic assessed the pipe surface at 18 points, covering approximately 21 feet out of the 323 total length of exposed pipe, using a Wintac WT100A calibrated on 11 January 2024. The following table summarizes the results which are broadly similar to the 2022 measurements taken in similar locations by PICA for Stantec.

Table 4: Summary of wall thickness measurements 2024

Figure 7: Ultrasonic testing at P20 (29°16'31.29"N, 103°19'12.04"W) min max avg min max avg max avg P2 0.198 0.254 0.226 0.201 0.216 0.207 8.3% 0.357 0.270 P3 0.198 0.254 0.226 0.215 0.215 0.215 5.1% 0.165 0.165 P4 0.198 0.254 0.226 0.205 0.209 0.207 8.3% 0.306 0.271 P5 0.198 0.254 0.226 0.209 0.213 0.211 6.8% 0.249 0.221 P6 0.198 0.254 0.226 0.209 0.22 0.215 5.1% 0.249 0.165 P7 0.198 0.254 0.226 0.209 0.213 0.211 6.7% 0.249 0.219 P8 0.198 0.254 0.226 0.205 0.213 0.208 8.1% 0.306 0.264 P12 0.198 0.254 0.226 0.201 0.209 0.206 9.1% 0.363 0.295 P13 0.198 0.254 0.226 0.203 0.211 0.207 8.2% 0.334 0.266 P15 0.198 0.254 0.226 0.196 0.206 0.201 11.1% 0.431 0.361 P16 0.198 0.254 0.226 0.196 0.209 0.203 10.0% 0.431 0.324 P17 0.198 0.254 0.226 0.199 0.232 0.209 7.3% 0.391 0.238 P19 0.198 0.254 0.226 0.198 0.204 0.202 10.8% 0.397 0.351 P20 0.198 0.254 0.226 0.205 0.219 0.210 7.2% 0.306 0.235 P21 0.198 0.254 0.226 0.196 0.204 0.199 11.8% 0.432 0.384 P29 0.198 0.254 0.226 0.215 0.238 0.228 1.0% 0.165 0.000 P30 0.198 0.254 0.226 0.204 0.224 0.212 6.1% 0.317 0.200 P31 0.198 0.254 0.226 0.201 0.216 0.207 8.3% 0.357 0.270

Location Wall thickness (inches)

Δ Annual Loss Rate (mil/yr.)1955 2024

DETAILED PIPE-WALL CONDITION ASSESSMENT

RESULTS

DETAILED PIPE-WALL CONDITION ASSESSMENT RESULTS

Figure 8: PII Test Segment Map

The following table summarizes the minimum average effective wall thickness for each section of pipe. These minimum values represent the lowest values obtained from the PII testing less 5% to account for measurement error. As these are the average value over a length of pipe, they are not directly comparable to the ultrasonic results presented earlier.

Table 5: Summary of PII wall thickness measurements

PipeSonic estimates that over 95% of the material loss has been internal due to the limited surface corrosion seen on site. Although it is challenging to compare the ultrasonic tests as they represent “spot” checks, the rate of wall loss appears to have increased very slightly from 2002 to

2024, possibly due to loss of internal coating.

Table 6: Comparison of minimum wall thickness and annual wall loss rates

Figure 9: P7 (29°16'57.26"N, 103°19'56.24"W)

Figure 10:P28 (29°16'12.18"N, 103°18'15.25"W) min Max

0.197 0.254

2002 Ultrasound 0.216 0.0008 2022 Ultrasound 0.187 0.0010 2024 Ultrasound 0.204 0.0007

2024 PII 0.193 0.0009

Thickness (in)Year Annualized Loss (in)

REMAINING SERVICE LIFE / END OF ECONOMIC SERVICE

The most basic method of forecasting the remaining service life is to assume a constant linear loss based on the original wall thickness and the present values. This was the method adopted by Stantec in their 2022 report where they calculated the remaining service life (RSL in years) as follows: 𝑅𝑆𝐿 = ℎ𝑝𝑟𝑒𝑠𝑒𝑛𝑡−ℎ𝑚𝑖𝑛 ℎ𝑛𝑒𝑤−ℎ𝑝𝑟𝑒𝑠𝑒𝑛𝑡 × 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 𝑦𝑒𝑎𝑟 − 𝑌𝑒𝑎𝑟 𝑖𝑛𝑡𝑎𝑙𝑙𝑒𝑑5

Table 7 summarizes results for each pipe segment using this formalism with the corrected ℎ𝑚𝑖𝑛 value of 0.089 and corrected annualized loss rates taken from the 2024 field measurements.

Table 7: Remaining surface life at constant wall loss

Table 8: Estimated remaining min,wall thickness 2024/50

5 Big Bend National Park Condition Assessment of Park Water Systems /BIBE 317515 / Stantec #17731165 Nov 23 2022 Pg 18-19

ID Start End S1 P1 P2 315.8 0.188 0.00055 180 S2 P2 P3 423.6 0.215 0.00016 790 S3 P3 P4 297.7 0.204 0.00031 374 S4 P4 P5 101.3 0.208 0.00026 465 S5 P5 P6 131.0 0.212 0.00021 593 S6 P6 P7 492.0 0.199 0.00038 288 S7 P7 P8 673.5 0.190 0.00052 193 S8 P8 P12 1,485.7 0.191 0.00050 205

S10 P12 P13 509.1 0.189 0.00053 187 S11 P13 P14 395.1 0.212 0.00020 616 S12 P14 P15 764.2 0.194 0.00046 226 S13 P15 P16 308.1 0.206 0.00028 415 S14 P16 P17 686.6 0.196 0.00043 246 S15 P17 P19 1,192.9 0.181 0.00065 141 S16 P19 P20 326.0 0.181 0.00065 141 S17 P20 P22 1,195.8 0.187 0.00055 178 S18 P22 P28 4,471.1 0.190 0.00051 198 S19 P28 P30 413.7 0.216 0.00015 849 S20 P30 P31 315.0 0.209 0.00024 490 S21 P31 P32 533.8 0.203 0.00033 346

Corrosion rate (in/yr)

RSL2024 Min Thickness

Segment Length (ft)

Year Constant Loss Accelerating Loss 2024 0.1930 0.1930 2025 0.1921 0.1921 2026 0.1912 0.1911 2027 0.1903 0.1901 2028 0.1895 0.1890 2029 0.1886 0.1878 2030 0.1877 0.1866 2031 0.1868 0.1853 2032 0.1859 0.1839 2033 0.1850 0.1825 2034 0.1842 0.1810 2035 0.1833 0.1793 2036 0.1824 0.1776 2037 0.1815 0.1758 2038 0.1806 0.1739 2039 0.1797 0.1719 2040 0.1789 0.1697 2041 0.1780 0.1675 2042 0.1771 0.1651 2043 0.1762 0.1626 2044 0.1753 0.1599 2045 0.1744 0.1570 2046 0.1736 0.1541 2047 0.1727 0.1509 2048 0.1718 0.1475 2049 0.1709 0.1440 2050 0.1700 0.1440

The constant loss method provides an unrealistic picture of the pipe’s remaining service life. A more realistic model can be formulated by recalling that corrosion losses on pipes such as the fill line in Big Bend which suffer limited external pitting are proportional to the inner surface area which is proportional to the inner diameter 𝐷and the segment length:

𝜕ℎ

𝜕𝑡

= −𝛽𝐷(𝑡) → 𝐷(𝑡) = 𝑂𝐷0 − 2ℎ(𝑡)

As the pipe wall thins over time, the inner radius increases:

ℎ(𝑡) = 0.5𝑂𝐷0 − (0.5𝑂𝐷0 − ℎ0)𝑒2𝛽𝑡

Bear in mind as well that higher operating pressures will require both a thicker ℎ𝑚𝑖𝑛 and increase the rate of wall loss even faster as the pipe wall expands out further in response to the increased pressures.

ℎ𝑚𝑖𝑛 as calculated using the AWWA method previously described also overestimate remaining life by setting the end of life as the point of actual failure. Instead, a probabilistic value should be computed which minimises the potential for failure to less than the average annual failure rate for similar pipes.

Using data from Utah State University6 this value is ℎ𝑚𝑖𝑛 = 0.156. Using that value of ℎ𝑚𝑖𝑛 and the area-based formalism set out above, the estimated remaining service life decreases to a more realistic estimate of 40 years remaining safe operating life for the thinnest portions of pipeline.

Figure 11traces the wall loss for the weakest segment of the fill line from its installation through to its present value (green diamond) through to its estimated end of economic life in 2064 (red diamond).

6 See: Folkman, Steven, "Water Main Break Rates In the USA and Canada: A Comprehensive Study" (2018). Mechanical and

Aerospace Engineering Faculty Publications and Barfuss, S. "Water Main Break Rates In the USA and Canada: A Comprehensive Study" (2023). Mechanical and Aerospace Engineering Faculty Publications

Figure 11: Estimated end of safe operating life for S15

Assuming operating conditions remain the same, reinspecting the pipe using PipeSonic’s PII technology in 3-4 years would allow for a more accurate estimation of the remaining service life.

If the pipe’s operating conditions change, especially if the regular operating pressures or flow rates increase, then the inspection should happen sooner, ideally right after completion of the modifications to better quantify the effect of these changes on the pipe’s remaining service life.

Figure 12: Testing at P1 29°16'54.94"N, 103°20'14.48"W)

Figure 13 P2 (29°16'55.40"N, 103°20'10.99"W)

Figure 14: Inlet at treatment plant

DETAILED CONDITION ASSESSMENT RESULTS

The following charts present the variations in wall thickness vs distance for the pipe length at a resolution of 30 feet. This means that the value represents a rolling average centred every 30 feet along the pipeline. This is a result of the best propagating test signals which have a wavelength of approximately 15 feet.

SEGMENT 1

SEGMENT 2

SEGMENT 3

SEGMENT 4

SEGMENT 5

SEGMENT 6

SEGMENT 7

SEGMENT 8

SEGMENT 9

SEGMENT 10

SEGMENT 11

SEGMENT 12

SEGMENT 13

SEGMENT 14

SEGMENT 15

SEGMENT 16

SEGMENT 17

SEGMENT 18

SEGMENT 19

SEGMENT 20

SEGMENT 21

EXPOSED PIPE SEGMENTS

EXPOSED PIPE SEGMENTS

Approximately 3% of the pipe surface is exposed to the elements. While a few of these exposed areas, particularly those in the drainage area which are occasionally submerged, do show some evidence of minor to moderate surface pitting, most of the exposed pipe surface retains at least some of the original surface coating or other protective patina. The average wall thickness measured at these points in 2024 was approximately .209" or 93% of the original wall thickness.

Most of the wall loss is due to internal corrosion.

In the areas heighted in yellow in Appendix 2, the pipe is either located in the drainage area or is in the hiking path and subject to foot traffic. These areas total approximately 323 linear feet (±5').

Should the Park Service desire to extend the life of these segments, it could be beneficial to clean these surfaces, re-coat them with a protective epoxy or other coating, and where appropriate, either encase the pipe in concrete or burry it with light native cover. Untreated pipe should not be buried in concrete.

SUMMARY & RECOMENDATIONS

Based on the results of the PII assessment and the updated pipe materials obtained from the Crane catalogues, the fill line appears to be in good condition for a pipe of its age. No segments appear to be at risk of imminent failure and no active leaks were discovered.

If no changes are made to the basic operating conditions, and the exposed pipe segments are provided with improved protection from moisture and human traffic then a remaining service life of up to 40 years is possible for the weakest pipe segments, and over 50 years for the other portions of the line. These estimates can and should be verified by another inspection of the weakest pipe segments (S1, S7, S10, S15, S16, and S17) in 3-4 years. If operating conditions change, especially if pressures or flow rates increase, then reinspection of those segments should be completed sooner.

APPENDIX 1: LEAK DETECTION VIA CORRELATION

APPENDIX 1: LEAK DETECTION VIA CORRELATION

Non-invasive acoustic leak detection via correlation is based on the ability to measure sounds from water leaks. Sounds are assumed to propagate at a speed (𝑐) that is characteristic of the pipe material and geometry. Figure 15 illustrates the scenario where two sensors are installed on a pipe and a leak is at a distance 𝐿1 from sensor 𝑆1. The leak sound requires 𝐿1/𝑐 seconds to travel from the leak location to the sensor. Similarly, the leak signal reaches sensor 𝑆2 in (𝐿 − 𝐿1)/𝑐.

The arrival time difference (𝐿 − 2𝐿1)/𝑐 may be determined by cross-correlating the two signals. If 𝑐 is known, 𝐿1 can be determined. Commercial instruments such as the Gutermann Aquascan are convenient tools.

Figure 15: Leak detection arrangement.

Sensors S1 and S2 are usually positioned on valves or hydrants.

APPENDIX 3: POTENTIAL REMEDIATION SITES FOR

EXPOSED PIPE

APPENDIX 3: POTENTIAL REMEDIATION SITES FOR EXPOSED PIPE

APPENDIX 4: INSPECTION IMAGES

Table 9: Air Release Valve Images

Table 10: Oak Spring pump house interior images

Table 11: Blow-off valve (29°16'44.43"N, 103°19'38.40"W)

Table 12: Repair clamp (29°16'51.83"N, 103°19'46.11"W)

Table 13: P12 ( 29°16'50.64"N, 103°19'44.78"W

Table 14: Distressed Pipe (29°16'41.10"N, 103°19'31.92"W)

Table 15 P22 (29°16'31.65"N, 103°18'59.35"W)

Table 16: Various Test Points

Figure 16: P15 (29°16'43.15"N, 103°19'30.34"W)

Figure 17: P17 (29°16'37.42"N, 103°19'26.87"W)

Figure 18: P31 (29°16'5.04"N, 103°18'10.83"W)

Figure 19: P16 (29°16'41.14"N, 103°19'31.93"W)

Figure 20: P16 (29°16'41.14"N, 103°19'31.93"W)

Figure 21: P16 (29°16'41.14"N, 103°19'31.93"W)

Table 17: Exposed pipe at trail head (P30, 29°16'9.07"N, 103°18'12.85"W)

Table 18: Exposed Pipe ( 29°16'7.57"N, 103°18'12.28"W)

Table 19 Exposed Pipe (29°16'7.57"N, 103°18'12.28"W)

Table 20: Exposed Pipe (29°16'50.78"N, 103°19'45.21"W)

Table 21: P19 (29°16'32.15"N, 103°19'15.71"W)

Table 22: Exposed Pipe (29°16'52.02"N, 103°19'46.30"W)

Table 23 Exposed pipe (29°16'51.35"N, 103°19'45.59"W)

Table 24: Exposed Pipe ( 29°16'53.15"N, 103°19'46.47"W)

Table 25: Exposed pipe (29°16'52.59"N, 103°19'46.68"W)

Table 26 P31 (P31 (29°16'5.04"N, 103°18'10.83"W)

Figure 22: Exposed pipe (29°16'42.81"N,103°19'30.28"W)

Figure 23: P10 (29°16'54.91"N, 103°19'46.24"W)

Figure 24: P11 (29°16'52.58"N, 103°19'46.69"W)\