Contact Us

Force Main Inspections

Get a Quote
force main inspections

Introduction

Force mains are a pressurized component of gravity sewer systems that transport wastewater to a discharge point. They are advantageous in areas where challenging topography prevents the use of a gravity-reliant system, as they reduce the size and depth of sewers and decrease construction and maintenance costs. However, force mains are challenging to maintain, inspect, and repair due to the inability to take them offline for extended periods and the limited access points for inspection or maintenance. Traditional inspection methods like televising, flushing, or jetting are not effective for force mains, leading to their exclusion from regular assessment and maintenance programs. As a result, municipalities are often forced to react to force main failures rather than prevent them. Pipers® represent a solution that provides a phased, cost-effective way to identify defects and separate the good pipelines from the bad.
See Case Study

Force main risks

The vast majority of force main failures can be attributed to three main factors: internal corrosion, structural deterioration, and low sourcing velocity. A good understanding of the force main and its high-risk locations is an integral part of force main risk management.

  • Internal Corrosion

    Over 60% of existing force mains are composed of ferrous materials like steel, cast iron, and ductile iron. The primary cause of failure in these force mains is internal corrosion due to hydrogen sulfide (H2S) gas. Increased amounts of H2S in wastewater can be caused by high retention times at pump stations and low velocity flow which results in long travel times. H2S can then form into gas pockets at high elevation points. Air release valves are essential in mitigating gas pockets and the subsequent hydrogen sulfide damage that occurs at high elevation locations.

  • Hydraulic grade line inspection

    While moving through a pipeline, Pipers® measure the pressure. This pressure is a combination of pipeline characteristics (e.g. pipeline roughness, inside diameter, and elevation) and operational characteristics (e.g. speed). The hydraulic grade line (HGL) is calculated based on the measured pressure and the force main elevation to account for the effects of hydrostatic pressure changes (i.e., pressure increases caused by the force main descending and pressure decreases caused by it climbing). The hydraulic grade line indicates the amount of frictional pressure loss throughout the force main, where regions of the hydraulic grade line with a steeper slope experience more flow friction suggesting increased internal surface roughness and/or diameter restrictions.

  • Low Sourcing Velocity

    The minimum self-cleaning velocity for a force main is two feet per second. Below this velocity, deposits can build up which will restrict capacity and can be a risk for abrasion over time. Low points are at risk of significant deposit buildup if a self-cleaning velocity is not achieved. In addition, heavier particles in the wastewater can accumulate forming a solid deposit which can result in a flow regime with a sliding bed or an abrasion. Both types of solid deposits can cause long-term force main problems if left unaddressed. Finally, gas pocket formation is more likely to occur at slower velocities.

Pipers® comprehensive inspection of force mains

From the force main risks section it has become clear that gas pockets at high points and deposits at low points jeopardize force main safety. Pipers®, INGU’s free-floating inspection tools, provide a comprehensive assessment of force mains. Pipers® effectively identify gas pockets (and leaks), deposits, and magnetic features in a single inspection. The free-floating design allows Pipers® to navigate the force main’s flow without getting stuck in air release valves or regions with significant gas pockets, deposits, or tees.

solution e - Force Main Inspections

Gas Pocket Detection

The Pipers® record sounds caused by gas pockets, pumps, and other noise sources in the pipeline. Gas pockets are usually louder than the background noise in the pipeline and can be confirmed by the specific spectral signature at its location. The spectral signature of a gas pocket can be distinguished from a leak because they are generally spread out and appear abruptly, whereas a leak is a point source with a single intense peak that fades away on each side.

solution f - Force Main Inspections

Hydraulic Grade Line Inspection

While moving through a pipeline, Pipers® measure the pressure. This pressure is a combination of pipeline characteristics (e.g. pipeline roughness, inside diameter, and elevation) and operational characteristics (e.g. speed). The hydraulic grade line (HGL) is calculated based on the measured pressure and the force main elevation to account for the effects of hydrostatic pressure changes (i.e., pressure increases caused by the force main descending and pressure decreases caused by it climbing). The hydraulic grade line indicates the amount of frictional pressure loss throughout the force main, where regions of the hydraulic grade line with a steeper slope experience more flow friction suggesting increased internal surface roughness and/or diameter restrictions.

solution b - Force Main Inspections

Magnetic Inspection

Pipers® measure the magnetic flux density (MFD) inside pipelines using passive tri-axial magnetic flux sensors. In the analysis process of ferromagnetic pipelines, joints and spools are identified. The main part of the Pipers® MFD analysis is focused around characterizing the spools. Spools with a different magnetic flux density compared to surrounding spools are identified as outlier spools. These outlier spools are then labeled with the most probable cause, e.g. metal loss and pipeline features (ARVs, casings, …).

solution i - Force Main Inspections

Leak Detection

Pipers® record all sounds while moving with the flow through the pipeline making them sensitive to even the smallest leaks.

Want to see INGU Pipers® in action?

See Case Studies
force main inspections

Over 100 Force Main Inspections

INGU’s Pipers® have inspected over 100 force mains across the United States and Canada. These inspections encompassed a wide range of pipeline lengths, from 0.05 to 70 miles, and diameters, from 3 to 108 inches. The force mains inspected were composed of both metallic materials (such as ductile iron and cast iron) and non-metallic materials (such as PVC and HDPE), and were designed for various pressure ranges.
Request a Quote

Stay in the loop