Ensuring safety during industrial fluid system maintenance is critical. The pressure or flow within a single line poses a significant risk to technicians working on gauges or measurement devices. As a best practice, isolating any fluid system line before maintenance is a fundamental safety measure.
Industry standards recommend the use of two block valves in sequence when bleeding out an energized leg in a fluid system. This double block valve setup is among the safest ways to achieve zero pressure and zero flow, ensuring a secure working environment.
Engineers typically employ one of two methods when designing block valve isolation configurations. The first involves adding a third valve between the two block valves to vent or bleed off any residual pressure that may be leaking from the first valve. The second approach utilizes a third valve to divert flow around the section under maintenance via a bypass loop. Both methods enhance safety and efficiency during system isolation and maintenance.
Key Locations for Isolation Configurations in a Plant
To maintain industrial fluid systems safely, technicians must have the means to isolate specific lines effectively. Essential locations requiring isolation configurations include:
- Devices or components that require regular maintenance, such as filters, valves, or transmitters.
- Systems, skids, or pipelines needing reconfiguration, repair, or replacement.
- Sections of the main process piping requiring servicing or maintenance.
- Instrumentation lines branching off the process line, such as sampling stations or measurement devices.
- Sampling systems with calibration fluids or streams that are periodically switched on or off.
Isolation Configuration Options
To prevent unintentional pressure buildup due to valve leakage, industry best practices discourage reliance on a single block valve. Instead, two main configurations are recommended for isolating fluid lines:
1. Double Block and Bleed (DBB) Configuration
A double block and bleed (DBB) setup is a simple and effective method for isolating a fluid system. It is commonly used in process-to-instrumentation transitions, where process interface valves isolate the instrument. This configuration consists of two block valves with a bleed valve positioned between them to vent any trapped pressure.
2. Bypass Loop Configuration
A bypass loop not only isolates the section under maintenance but also redirects fluid flow to maintain system operation. In this configuration, the first block valve may be a three-way valve that diverts flow around the maintenance area, reducing downtime. Bypass loops are particularly useful in preventing hydraulic shock, or “water hammer,” which can occur due to sudden shutoff events.
Depressurization and Safety Considerations
Before maintenance begins, depressurizing the fluid system is crucial. A best practice is to employ two sequential block valves to prevent pressure buildup in the isolated section. While high-quality valves are designed for tight shutoff, leaks may still occur due to factors such as temperature fluctuations, improper maintenance, or valve mis selection.
To mitigate such risks, it is advisable to use a second block valve along with a bleed valve. For continuous operations where downtime is not feasible, a bypass loop configuration can maintain system integrity while allowing for component replacement.
Choosing the Right Block Valves
The two most common block valve types in instrumentation lines are ball valves and needle valves. Selecting the appropriate valve is essential to maintaining system safety and efficiency.
Ball Valves
- Ideal for quick shutoff and high flow applications.
- Provide clear visual flow indication through handle positioning.
- Can cause hydraulic shock if closed suddenly, potentially damaging upstream equipment.
- Best used with a bypass loop to prevent sudden pressure spikes.
Needle Valves
- Designed for gradual shutoff, preventing hydraulic shock.
- Suitable for flow control and metering applications.
- Certain designs include rotating or soft stem tips to minimize leakage risk.
Integral Double Block and Bleed (DBB) Valves
- Reduce potential leak points and simplify installation.
- Offer compact, space-efficient solutions for critical shutoff applications.
- Help to achieve positive isolation against upstream pressure.
- Enable in situ calibration of downstream field instruments.
- Provide an extra layer of safety against failures.
Avoid using non-shutoff components, such as pressure regulators, in isolation configurations. While regulators can reduce flow, they are not designed for complete shutoff. A proper block valve should be installed upstream for safety.
Additionally, installing a pressure indicator downstream of the second block valve is a best practice to allow for visual pressure checks before maintenance begins.
Enhancing System Safety and Reliability
Proper isolation of fluid system lines with block valves enhances maintenance safety and boosts system uptime and plant efficiency. BMT’s Double Block and Bleed valves are designed to meet the fugitive emission requirements such as ISO 15848 parts 1 &2.
To learn more about best practices for fluid system configuration and training opportunities, contact BMT Superlok’s team of experts today. Contact Us