Pacific Flow Control recently completed a 42-inch Double Block and Bleed (DBB) line stop on AWWA C303 pipe, providing the additional level of pipeline isolation required for downstream confined-space work.
This project is a good example of how the requirements of the work taking place downstream can determine the type of line stopping solution needed. Installing a line stop is not simply about stopping flow. When workers need to enter a confined space, the isolation method must also address the specific safety requirements associated with that work.
Why Double Block and Bleed Isolation Was Needed
For this project, work was being performed in a downstream confined space. A conventional single isolation point would not provide the required isolation arrangement for the planned confined-space entry.
Under WorkSafe's confined-space requirements, certain situations involving adjacent piping can require isolation through methods such as disconnecting, blanks or blinds, or an acceptable Double Block and Bleed system. For substances that are hazardous because of pressure, temperature, or quantity, the regulations also provide for other appropriately engineered isolation methods.
This meant the isolation strategy had to be considered as part of the overall project design rather than simply installing a standard single line stop.
What Is Double Block and Bleed (DBB) Isolation?
Double Block and Bleed, commonly referred to as DBB isolation, uses two isolation barriers with a bleed point between them. The purpose of this configuration is to provide an additional level of protection between the live pipeline and the downstream work area.
The space between the two isolation points can be monitored or relieved through the bleed. If the upstream isolation point allows material to pass, the bleed provides a means of identifying and managing that leakage rather than relying solely on a single barrier.
WorkSafe's requirements for a DBB system include provisions for the bleed arrangement, verification of the downstream block's ability to withstand line pressure, lockout, and monitoring to ensure the bleed remains unobstructed while the confined space is occupied.
Double Block and Bleed Isolation Options
The diagram below shows several examples of Double Block and Bleed (DBB) isolation configurations that can be performed by Pacific Flow Control. Depending on the existing pipeline infrastructure, site conditions, and project-specific isolation requirements, DBB can be achieved using different combinations of line stops, existing line valves, valve inserts, nitrogen line freezing, and hot-tapped bleed points.
Every pipeline and confined-space application is different. Our team can evaluate the existing system and develop a Double Block and Bleed solution tailored to the specific requirements of the project, helping provide the necessary isolation while minimizing shutdowns and modifications to existing infrastructure.
Two Isolation Points, Different Ways to Get There
When additional isolation is required, the appropriate solution depends on the pipeline configuration, site conditions, available space, operating pressure, and requirements of the downstream work.
One approach may involve installing a second independent line stop, creating two separate isolation points.
Another option may be to design a Double Block and Bleed line stopping configuration that provides the necessary dual isolation and bleed arrangement for the application.
Determining the right method before mobilization is critical. On a 42-inch AWWA C303 pipeline, adding another stop can have significant implications for excavation requirements, fittings, equipment, installation time, and overall project cost.
Planning Isolation Before the Work Begins
This project demonstrates why it is important to understand exactly what will happen downstream of a line stop before selecting an isolation method.
Before designing a line stopping solution, several factors should be considered:
- Will workers be entering a confined space?
- What level of isolation is required for the planned work?
- Is a single line stop sufficient for the application?
- Is secondary isolation required?
- Can a second line stop be installed?
- Can a DBB configuration provide the required isolation?
- What are the pipe material, diameter, operating pressure, and site constraints?
- Does the proposed isolation method require engineering review or certification?
Addressing these questions during the planning stage can help prevent field changes, additional excavation, project delays, and unexpected costs.
Specialized Line Stopping Solutions from Pacific Flow Control
Every live pipeline project is different. Pacific Flow Control provides specialized line stopping, Double Block and Bleed isolation, hot tapping, bypass, valve insertion, and other live pipeline solutions for municipal, utility, and industrial infrastructure.
This recent 42-inch DBB line stop on AWWA C303 pipe demonstrates how the right isolation strategy can be developed around both the pipeline itself and the work that needs to happen downstream.
If your project involves confined-space entry, large-diameter pipe, limited existing isolation, or complex shutdown requirements, contact Pacific Flow Control. Our team can review the application and help develop a line stopping and isolation solution designed around the specific requirements of your project.