project profile

INDUSTRY
NATURAL GAS

APPLICATION
CURED-IN-PLACE-LINING

CLIENT
BGE

background & situation

A 42” cast iron main in Baltimore, a critical source for gas, had been repaired over 75 times with internal clamps/mechanical seals. The large diameter original main, dating back to the 1900s, was buried more than 10 feet, under businesses, a school and a residential area. It also crossed under a railroad bridge . Baltimore Gas and Electric (BGE) looked to Progressive Pipeline Management (PPM) and Miller Construction to rehabilitate the 840 feet segment with Starline® Cured-in-Place-Lining (CIPL)  in approximately three weeks.

BGE ruled out replacing the gas main for multiple reasons. Replacement estimates were very high, there would have been significant disruption and a complex permitting process.  Full ‘trench and replace’ would have required road closures, costly excavation over every connecting joint, and expensive steel pipe. Multiple permits would have been needed to dig under the railroad bridge. Businesses, residents and the K-12 school would have experienced a long disruption.

CIPL was a cost-effective and critical strategy for leak reduction, and allowed the utility to take advantage of the 100+ years of additional life that CIPL can restore back into their pipeline inventory.

Scope

Once project plans were set, the utility and Miller Construction excavated three access pits, and organized any shutdowns and diversion to the gas service lines. Miller Construction removed the 75 internal clamps  and mechanical seals that had been installed to prevent leaks.  

The project was divided into two segments. The first, 208 feet long, included four 90-degree vertical bends and two 45-degree vertical bends. After the first 90-degree bend, a 42-inch drip pot located 18.5 feet deep required special attention. A stainless steel bridge was built and installed by Miller Construction to support the inversion and protect against unintended over-pressurization within the annular space of the drip pot fitting.

The second segment, 532 feet long, included three 45-degree bends and a 16-inch service tee that was being abandoned, leaving a void in the pipe. Before lining, PPM installed a structural reinforcement patch (SRP) inside the pipe at the tee fitting.

CCTV crawlers and advanced multi-camera models were used to inspect anomalies or unaccounted for structural defects. The internal pipe surface was cleaned and prepared using grit and a special tool called a spin blaster. Two high-CFM rated dust collecting vacuum units, creating over 50mph airflow, were deployed to reclaim the grit.  A second CCTV inspection confirmed the segment was clean, clear and ready for lining.

The installation process began by loading the large diameter material into a large remotely steerable pressure drum. The liner was pneumatically inverted and maneuvered through the pipeline while maintaining 8-psi during the ambient temperature curing. A bluetooth/cellular remote pressure device provided real-time pressure readings of the internal curing along with any possible fluctuations.  PPM improved work-flow efficiency and preserved the workspace with a unique anchoring device.  While segment one was curing, the crew simultaneously cleaned and lined the second segment.

After curing, the liner was depressurized and the ends cut out. Final post-lining CCTV inspection confirmed that the liner was perfectly bonded to the host pipe. BGE performed a standard 25-lb 24-hour pressure test before putting the main back online.

Challenges

A major challenge was working within the confined space of the lining pit, located in an alley behind an industrial business. The excavated pit was 15 feet deep and 25 feet long, bordered by a brick foundation wall and a loading dock. There was extremely tight spacing for the heavy vehicles and crews required for cleaning, sand blasting and lining. Fast-moving crews had to have access to move, set up and operate the equipment. To lift equipment in and out of the constrained space, BGE brought in a crane. 

Ensuring environmental and safety compliance was also critical. The geometry of the pipe and the depth of the pits meant that crews were working up to 8 hours a day inside a trench. Safety protocols and confined space entry procedures for BGE and PPM were put in place to protect the crews performing the clamp removals inside the pit.  

Another major concern was water infiltration. The pipeline and excavations were below the water table for Baltimore. Water from a nearby culvert was deemed a significant contamination risk.  As a safety precaution, BGE employed an environmental subcontractor to keep pumps running 24/7, preventing flooding and protecting the nearby stormwater system.

OUTCOMES & RESULTS

Due to excellent planning, preparation and collaboration, the lining was completed ahead of schedule. Disruption to the community was minimal. Excavation and trenching did not extend into the roadway and traffic flowed with minimal interruptions. Each segment’s cleaning, inspection, lining and curing took approximately three days.

Rehabilitating the 42-inch pipeline with 3 pits in total over three weeks proved far more viable than full replacement. The decision to line resulted in significant cost and time savings. Had BG&E opted for replacement of the main, deep pits would have been excavated every twelve feet. Excavating under the railroad bridge may have been nearly impossible because of the embedded steel pillars. Costs of materials, excavations and environmental compliance would have been extraordinary.