State of Technology Report for Force Main Rehabilitation, Final ...

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2.5 Redundancy Many force mains are located at critical points in sewerage systems. As a result, if they have to be taken out of service due to a failure, then by-pass pumping or the use of honey trucks is necessary. One way in which utilities plan for this is to install dual parallel force mains thus providing redundancy. During an emergency, such as a failure in one line, the parallel line can be used to maintain a minimal level of flow such that any upstream wetwell does not overflow or sewers become surcharged, or at least the use of honey trucks (required to keep the sewage from swamping any lift stations) is minimized. The other advantage in having a redundant line is the ability to take one line out of service for an intrusive (internal) inspection and/or repairs. Over 45% of utilities contacted indicated that they had at least one redundant force main in their system. For those reporting in the affirmative, an average of 14% of the systems had some redundancy built in. However, some utilities actually reported in the WERF survey having a larger number of redundant systems than total force mains so this number is suspect. This limited sampling would suggest that perhaps about 5% of the total number of force mains do have some redundancy built in. Parallel mains to enable one main to be out of service are seldom installed. Those utilities that do have parallel mains generally installed them because extra capacity was needed over and above that available from an existing main. The parallel main is then installed to provide additional capacity and not the total capacity. Thus, the opportunity for redundancy and operational security is not taken. Current practice is not to install parallel mains to provide redundancy. Installing alongside existing mains considered critical is done only very occasionally. 2.6 Cause of Failure in Force Mains Based on the WERF survey, almost universally, with 92% of the responders in the affirmative, utilities attempt to identify the cause of the failure in the force main. The utilities were asked to identify the most common factors relating to failures in their force mains. Various causes are discussed below. It is important to understand the typical failure modes and mechanisms of force mains in order to select the most appropriate repair, rehabilitation, and replacement technologies. 2.6.1 Ferrous Force Mains. Figure 2-6 shows that internal corrosion was rated as being responsible for ferrous force main failures 26.2% of the time, ahead of all other known causes. External corrosion at 19.2% and third-party damage at 19.4% are the next most common causes of failures. Combining internal and external corrosion, corrosion appears responsible for failures in force mains in nearly 46% of cases. After third-party damage, joint leakage at 15.2%, surge pressure at 10.2%, and insufficient capacity at 9.8% are the next most significant causes of force main failures. 2.6.2 Non-Ferrous Force Mains. Figure 2-7 shows the most common single cause of failure in non-ferrous force mains is third-party damage, which accounts for 36% of failures. Corrosion and structural failure together account for 54% of failures. It is considered likely that some of the structural failures reported for cementitious pipes (AC, RCP, and PCCP) are due to corrosion. Figure 2-7 is based on a weighted average of failure causes for each pipe material. The main causes of failure vary significantly by pipe material. For each pipe material type, the main causes of failure are as follows: (1) PVC – third-party damage, (2) PCCP – corrosion, (3) RCP – corrosion, (4) AC – third-party damage, and (5) PE – third-party damage. 9
Proper inspection of force mains would allow a utility to identify signs of corrosion and leakage, which represent 61% of the reported causes of failure in ferrous mains and 30% in non-ferrous mains. For example, with information on remaining wall thickness of ferrous mains, a utility could plan on repair, rehabilitation, or replacement before a force main fails. No amount of inspection can eliminate third party damage, which is the second leading cause of failure overall and the leading cause in non-ferrous mains. However, utilities can be prepared with proper emergency repair procedures in place. Figure 2-6. Causes of Failure in Ferrous Force Mains (WERF, 2009) Figure 2-7. Causes of Failure in Non-Ferrous Sewer Force Mains (WERF, 2009) 10
Page 1 and 2: EPA/600/R-10/044| March 2010 | www.
Page 3 and 4: DISCLAIMER The work reported in thi
Page 5 and 6: Introduction EXECUTIVE SUMMARY Forc
Page 7 and 8: The use of close-fit liners is ofte
Page 9 and 10: A whole host of ASTM specifications
Page 11 and 12: CONTENTS DISCLAIMER ...............
Page 13 and 14: 6.0: OPERATION AND MAINTENANCE.....
Page 15 and 16: DEFINITIONS Cured-in-place pipe (CI
Page 17 and 18: 3-D three-dimensional AASHTO ACP AR
Page 19 and 20: UV ultraviolet WERF Water Environme
Page 21 and 22: wastewater conveyance systems (EPA,
Page 23 and 24: • Section 8: Findings and Recomme
Page 25 and 26: Figure 2-2. Diameter Distribution o
Page 27: Figure 2-4. Location of Force Mains
Page 31 and 32: 0.03% of the overall length. There
Page 33 and 34: Table 3-1. Summary of Renewal Techn
Page 35 and 36: 3.3.3 Joint Repair 3.3.3.1 Internal
Page 37 and 38: more appropriate to a water main wh
Page 39 and 40: are, however, several communities (
Page 41 and 42: Table 3-3. Properties of Hunting Po
Page 43 and 44: 3.4.3.1 Symmetrical Reduction Close
Page 45 and 46: Rolldown Rolldown was developed in
Page 47 and 48: Subline Subline, offered by Subterr
Page 49 and 50: On-Site Expandable PVC Close-Fit Li
Page 51 and 52: 3.4.4.2 Semi-Structural CIPP Liners
Page 53 and 54: inch (150 mm) liner down to 60 psi
Page 55 and 56: 3.4.5.1 Adhesive-Backed Woven Hose
Page 57 and 58: US. Primus Line is a seamless, wove
Page 59 and 60: Figure 3-21. Summary of Replacement
Page 61 and 62: favorable to stringing out a long l
Page 63 and 64: 3.5.1.3 Pipe Slitting. Pipe slittin
Page 65 and 66: 4.1 4.0 TECHNOLOGY SELECTION CONSID
Page 67 and 68: head loss to maintain flow capacity
Page 69 and 70: ferrous main, this can be an intern
Page 71 and 72: 5.0 DESIGN AND QA/QC This section w
Page 73 and 74: thickness? It can still support the
Page 75 and 76: pipe’s design life. Once again, i
Page 77 and 78: ASTM F1533 The renewal process invo
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AWWA M55 PE Pipe - Design and Insta
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Most of the controversy over the ap
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up to each individual manufacturer.
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For pressure applications, a hydros
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Dimensional checks on the pipe diam
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5.6.2.3 CIPP Long-Term QA/QC Requir
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Figure 6-1. Polyurethane Pipeline C
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in currents or potentials indicate
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could also be used in force mains.
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7.0 GAPS BETWEEN NEEDS AND AVAILABL
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80 Table 7-1. Technology Gaps and C
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82 Table 8-1. Parameters for Evalua
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8.5 Sound, Risk-Based, Decision-Mak
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9.0 REFERENCES Aggarwal, S.C. and M
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Technology/Method Spray - On Lining
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Technology/Method Spray - On Lining
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Technology/Method Spray - on Lining
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Technology/Method Close Fit/Tension
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Technology/Method Close Fit PE/Symm
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Technology/Method Symmetrical Reduc
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Technology/Method Rolldown/Close Fi
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Technology/Method Subcoil/Close Fit
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Technology/Method PE Liner/ Cement
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Technology/Method Subline/Close Fit
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Technology/Method Fold and Form PE
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Technology/Method Fold -and - Form/
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Technology/Method Fold -and - Form/
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Technology/Method Fold -and - Form
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Technology/Method Fold -and - Form
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Technology/Method Close - Fit Linin
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Technology/Method CIPP/Pull In Plac
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Technology/Method CIPP/Inversion wi
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Technology/Method CIPP/Direct Inver
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Technology/Method CIPP/ Inversion a
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Technology/Method CIPP/Glass Fiber
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Technology/Method CIPP/Pull in Plac
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Technology/Method CIPP/UV Light Cur
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Technology/Method CIPP/Glass Reinfo
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Technology/Method CIPP with Carbon
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for Rehabilitated Sections V. Costs
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Technology/Method Woven Hose Lining
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Technology/Method Saertex - Liner®
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Technology/Method Hose Liner/Pulled
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Technology/Method Glass Reinforced
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Technology/Method Sliplining/HDD/Pi
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State of Technology Report for Force Main Rehabilitation, Final ...

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