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New Orleans Large Diameter Force Main Reliability

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In response to the impacts from Hurricanes Katrina and Rita, the Sewerage and Water Board of New Orleans (S&WB) renegotiated its Consent Decree with the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Justice (DOJ). These modifications included revised delivery of existing commitments and new obligations. Out of concern for the condition of S;amp;WB's two major sewer force mains (72- and 54-inch steel pipelines), the EPA required a reliability assessment to demonstrate that a replacement or installation of redundant force mains is not required.

The 66-/72-inch steel force main extends approximately 6 miles from Sewage Pump Station A (SPS A) to the East Bank Sewage Treatment Plant (EBSTP) and dates from 1975. The 54-/60- inch steel force main extends approximately 3 miles from SPS D to the EBSTP and dates from 1961. The force mains were protected from external corrosion with a coal tar enamel coating. At least some of the underground piping was wrapped with a fiberglass asbestos felt to protect the coal tar coating. The aboveground piping and the piping going through casing pipes was encased with a 2-inch cement mortar (gunite) coating to protect the coating. The pipelines included a number of “canal” crossings, including the Industrial Canal (a.k.a., the Inner Harbor Navigation Canal) which is a controlled (locks) open channel along its route between the Mississippi River and Lake Pontchatrain.

Due to the continuous operations of the SPSs A and D, as well as the various smaller pump stations that feed into the force mains, the force mains could not be shut down for any appreciable amount of time. Led by MWH global experts, a specialized team, including civil engineers, corrosion experts, and sampling and testing technicians executed a program of destructive and non-destructive testing and structural evaluation without adversely impacting S&WB's operations. Further, the testing and evaluation was performed with a compressed schedule in order to meet the Modified Consent Decree deadline.

The testing program to be detailed in this paper included:

Environmental database search

Visual inspection

Hydraulic model evaluation

Corrosion protection system inspection and potential testing

Coupon extraction for destructive testing

Non-destructive ultrasonic testing

Non-destructive guided wave testing

This paper will detail the results of the testing program and present the force main reliability conclusions based on the analysis and structural condition of the force mains.
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Keywords: condition assessment; force main reliability; steel force main structural evaluation

Document Type: Research Article

Publication date: 01 January 2011

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