Pipeline tie-ins are among the most demanding activities in pipeline construction, modification, maintenance, and expansion projects. A tie-in may be required when a new pipeline section must be connected to an existing operating line, when a branch connection needs to be installed, or when a section of pipeline must be isolated before modification.

The challenge becomes greater when the existing pipeline cannot simply be shut down.

In these situations, specialized intervention methods such as hot tapping, stopple isolation, and line stopping can allow work to be performed while maintaining some level of pipeline service. However, these methods are not interchangeable. Each has different objectives, equipment requirements, operating limitations, risks, and application conditions.

This field guide explains the differences between hot tap, stopple, and line stop methods and provides a practical framework for selecting the appropriate approach.

Important: Pipeline intervention work on operating or pressurized systems should be engineered and executed by qualified specialists using approved procedures, equipment, applicable codes, and project-specific risk controls. The information below is a technical overview, not a field procedure for performing a live-line intervention.

What Is a Pipeline Tie-In?

A pipeline tie-in is the connection of a new pipeline, branch, replacement section, equipment connection, or modification to an existing pipeline system.

Typical tie-in work can include:

• Connecting a new pipeline to an existing line
• Adding a branch connection
• Connecting a new facility to an operating pipeline
• Replacing a damaged pipeline section
• Installing a valve or fitting
• Modifying an existing pipeline network
• Connecting pipeline sections during expansion
• Isolating part of a system for maintenance

The tie-in method depends heavily on whether the existing pipeline can be taken out of service.

If a complete shutdown is possible, conventional isolation and tie-in methods may be sufficient.

If shutting down the pipeline would cause unacceptable operational or commercial consequences, engineered intervention methods may be considered.

Hot Tap, Stopple, and Line Stop: The Basic Difference

The easiest way to understand the three methods is to look at their primary purpose.

The important distinction is that hot tapping creates access, while line stopping and stopple systems are primarily associated with isolation.

In many complex projects, these methods are used together rather than as alternatives.

1. What Is Hot Tapping?

Hot tapping is a pipeline intervention method used to make a connection to an existing pipeline while it remains in service, subject to the suitability of the pipeline, fluid, operating conditions, equipment, procedure, and applicable requirements.

A typical hot-tap arrangement involves establishing a branch connection or fitting on the existing pipeline and using specialized equipment to create an opening through the fitting into the pipeline.

The opening can then provide access for a new connection, future intervention, or another engineered pipeline operation.

Typical Hot Tap Arrangement

A conceptual hot-tap system may include:

1. Existing pipeline
2. Welded or mechanically attached fitting
3. Isolation valve
4. Hot-tap machine
5. Cutting tool
6. Branch connection
7. Control and monitoring equipment

The exact configuration depends on the pipeline design and intervention method.

Why Use Hot Tapping?

Hot tapping may be considered when maintaining pipeline service is important.

Potential advantages include:

• Avoiding a full pipeline shutdown
• Maintaining supply to downstream users
• Connecting new branches to an operating line
• Reducing operational disruption
• Creating access for subsequent intervention work

However, hot tapping is not automatically suitable for every operating pipeline.

The pipeline material, wall thickness, fluid, pressure, temperature, flow conditions, fitting design, welding requirements, and operating history all need to be evaluated.

Hot Tap Does Not Mean “No Risk”

Because hot tapping involves intervention on an operating pipeline, engineering and procedural controls are critical.

Factors that may need assessment include:

• Pipeline wall thickness
• Corrosion and remaining wall
• Material properties
• Fluid composition
• Pressure
• Temperature
• Flow conditions
• Pipeline diameter
• Fitting design
• Welding procedure
• Heat input
• Ignition risk
• Hydrogen or other hazardous components
• Equipment compatibility
• Emergency response

A qualified engineering and specialist intervention team should establish whether the proposed hot-tap arrangement is suitable.

2. What Is a Line Stop?

A line stop is a temporary isolation technique used to restrict or stop flow through a pipeline at a selected location.

Unlike a hot tap, whose primary purpose is creating access, a line stop is intended to establish temporary isolation so that work can be carried out on a downstream or upstream section.

A line stop typically involves creating an engineered access point and installing a temporary stopping device inside the pipeline.

Why Use a Line Stop?

A line stop may be considered when:

• A pipeline section must be isolated
• A complete shutdown is undesirable
• Maintenance is required downstream
• A pipeline section needs modification
• A valve replacement is required
• A tie-in must be completed while other sections remain operational

The line-stop device temporarily changes the flow condition within the pipeline.

The exact stopping technology depends on the pipeline and intervention system.

Line Stop and Valve Isolation Are Not the Same

A permanent pipeline valve provides a designed isolation function as part of the pipeline system.

A line stop is generally a temporary intervention system installed specifically for the maintenance or modification activity.

This distinction is important when developing the isolation strategy.

A project may use a temporary line stop where an existing valve arrangement does not provide the required isolation or where installing/replacing permanent valves is part of the planned work.

3. What Is a Stopple?

“Stopple” is commonly used in pipeline intervention terminology to describe a specialized temporary pipeline isolation system.

Stopple systems are associated with installing a temporary stopping device inside a pipeline through an engineered intervention connection.

The system can allow a section of pipeline to be isolated while other parts of the system remain in service, subject to the design and operating conditions.

A stopple arrangement may involve:

• Hot tap connection
• Isolation valve
• Stopple machine
• Stopping head
• Bypass arrangement where required
• Pressure-control equipment
• Monitoring equipment

The exact system configuration depends on the pipeline application.

Why Use Stopple Isolation?

Stopple systems can be useful when a project requires temporary isolation of an operating pipeline without relying solely on a conventional shutdown.

Applications can include:

• Pipeline repair
• Valve replacement
• Pipeline modification
• Tie-in work
• Section replacement
• Maintenance activities
• Pipeline rerouting
• Facility modifications

A stopple operation is generally part of a broader engineered intervention plan rather than a simple piece of equipment that can be selected independently.

Hot Tap vs Stopple vs Line Stop

The terms are sometimes used interchangeably in informal discussions, but they describe different functions.

The key point is:

Hot tap = access/connection.

Line stop = temporary isolation.

Stopple = specialized temporary isolation system.

In actual projects, a hot tap can be the first step used to install the connection required for a line stop or stopple operation.

How a Typical Hot Tap and Stopple Project May Work

A simplified project sequence may look like this:

Existing pipeline ? Engineering assessment ? Hot-tap connection ? Isolation valve ? Intervention equipment ? Temporary isolation ? Tie-in/maintenance ? Reinstatement

This is a conceptual sequence only. Actual project procedures can vary significantly.

For example, a project may require two temporary isolation points so that a pipeline section can be isolated between them.

A bypass may also be installed where continued flow to downstream users is required.

The actual sequence should be developed and approved by the responsible engineering and specialist intervention team.

When Is Hot Tapping Considered?

Hot tapping can be considered when the primary requirement is to create a connection to an existing pipeline without taking the complete line out of service.

Typical examples include:

Adding a Branch Connection

A new branch pipeline needs to connect to an operating main line.

Connecting New Facilities

A new facility, processing unit, distribution section, or pipeline may need to connect to an existing system.

Installing Access for Intervention

A controlled access point may be required for subsequent pipeline intervention.

Supporting a Line-Stop Operation

A hot-tap connection may form part of a temporary isolation arrangement.

When Is Line Stopping Considered?

Line stopping becomes relevant when the project requires temporary isolation rather than simply access.

For example, imagine an operating pipeline that supplies a downstream facility.

The project requires replacement of a section upstream of that facility.

If shutting down the complete pipeline is undesirable or impractical, a temporary isolation system may be engineered so that the required section can be isolated while maintaining service elsewhere.

The actual feasibility depends on pipeline conditions and the proposed intervention design.

When Is Stopple Isolation Considered?

Stopple systems may be considered when a project requires a more specialized temporary isolation arrangement.

They can be particularly relevant for major pipeline modifications where isolation of a pipeline section is required while the remaining system continues operating.

Applications can include:

• Major pipeline tie-ins
• Pipeline replacement
• Valve replacement
• Sectional repairs
• Pipeline rerouting
• Facility expansion
• Temporary isolation during construction

The appropriate system should be selected based on the engineering requirements rather than simply choosing a “stopple machine” by pipe diameter.

The Role of Bypass Systems

Bypass arrangements can be an important part of temporary pipeline isolation.

Consider a pipeline that must remain operational while a section is isolated.

A bypass may allow controlled flow around the isolated section, depending on the system design.

A conceptual arrangement could be:

Pipeline flow ? Temporary isolation ? Bypass ? Temporary isolation ? Pipeline flow

The bypass design depends on:

• Required flow rate
• Pressure
• Fluid properties
• Pipeline diameter
• Available connection points
• Duration of isolation
• Temperature
• Operational requirements
• Hydraulic considerations

Bypass systems must be engineered specifically for the application.

Key Engineering Factors Before Selecting a Tie-In Method

The method should not be selected based solely on pipe diameter.

A proper assessment may include:

1. Pipeline Diameter

The pipeline size affects intervention equipment, fittings, access, and stopping technology.

2. Wall Thickness

Remaining wall thickness is particularly important for interventions involving welding or mechanical penetration.

Existing corrosion must also be considered.

3. Pipeline Material

The material grade can influence welding, cutting, temperature control, and equipment compatibility.

4. Internal Fluid

The fluid inside the pipeline is a major consideration.

Factors can include:

• Flammability
• Toxicity
• Corrosivity
• Temperature
• Pressure
• Phase
• Chemical composition

5. Operating Pressure

The intervention equipment and connection system must be suitable for the applicable operating conditions.

6. Operating Temperature

Temperature can influence equipment selection, welding conditions, seals, and intervention procedures.

7. Flow Conditions

Flow rate and velocity may influence hot-tap and isolation feasibility.

8. Pipeline Condition

Existing corrosion, erosion, cracking, deformation, coating condition, and previous repairs may affect suitability.

9. Required Isolation

Determine whether the project requires:

• No isolation
• Single temporary isolation
• Double isolation
• Isolation with bypass
• Permanent isolation
• Section replacement

10. Duration of Intervention

The required duration can influence equipment configuration and temporary works.

Hot Tap vs Line Stop: When the Functions Are Combined

One of the most important concepts for project planners is that hot tapping and line stopping are not necessarily competing methods.

They can be sequential parts of the same intervention.

For example:

Step 1: Establish a suitable hot-tap connection.

Step 2: Install an isolation valve.

Step 3: Introduce a temporary stopping device.

Step 4: Establish the required isolation.

Step 5: Perform the planned tie-in or maintenance work.

Step 6: Restore the pipeline to the required operating configuration.

The actual sequence, equipment, and controls must be established by the responsible specialist contractor.

Common Pipeline Tie-In Mistakes

Mistake 1: Treating Hot Tap and Line Stop as the Same Thing

Hot tapping primarily creates access, while line stopping provides temporary isolation.

Mistake 2: Selecting Equipment Only by Pipe Diameter

Equipment compatibility depends on more than diameter.

Operating pressure, temperature, wall thickness, fluid, material, fitting design, and isolation requirements also matter.

Mistake 3: Ignoring Existing Pipeline Condition

A new intervention connection should not be considered independently of the condition of the existing pipe.

Corrosion and reduced wall thickness can materially affect the engineering assessment.

Mistake 4: Assuming an Existing Valve Provides Adequate Isolation

Existing valve condition, leakage, configuration, and isolation requirements should be evaluated as part of the project isolation plan.

Mistake 5: Treating a Stopple as a Standalone Machine

Temporary isolation is a complete intervention system involving connections, valves, stopping equipment, pressure control, monitoring, and project procedures.

Mistake 6: Ignoring Fluid Hazards

The fluid inside the pipeline can fundamentally affect whether and how an intervention is performed.

Mistake 7: Failing to Plan Reinstatement

The intervention plan should consider not only installation and isolation but also how the pipeline will be returned to its intended operating configuration.

Field Checklist for Pipeline Tie-In Planning

Before selecting a hot tap, line stop, or stopple solution, the project team should establish:

Pipeline Information

• Nominal pipe size
• Actual outside diameter
• Wall thickness
• Material grade
• Pipeline age
• Corrosion history
• Previous repairs or modifications

Operating Information

• Operating pressure
• Operating temperature
• Flow rate
• Fluid composition
• Normal operating condition
• Required shutdown limitations

Tie-In Information

• New connection size
• Branch configuration
• Required isolation location
• Required isolation duration
• Bypass requirement
• Permanent or temporary modification
• Required reinstatement arrangement

Engineering Information

• Applicable codes and standards
• Approved drawings
• Welding requirements
• Inspection requirements
• Risk assessment
• Emergency response plan
• Specialist intervention requirements

This information gives the intervention contractor a much stronger basis for selecting the appropriate equipment and method.

Safety and Operational Considerations

Pipeline intervention on an operating system can involve significant hazards.

Potential hazards can include:

• High pressure
• Flammable fluids
• Toxic fluids
• Stored energy
• Hot work
• Loss of containment
• Fire or explosion
• Unexpected flow
• Equipment failure
• Pipeline integrity issues

For this reason, hot tapping, line stopping, and stopple operations should be handled by qualified personnel using engineered procedures and appropriate specialist equipment.

Important controls may include:

• Pipeline integrity assessment
• Engineering review
• Approved intervention procedure
• Permit-to-work system
• Isolation and contingency planning
• Pressure monitoring
• Equipment inspection
• Emergency response planning
• Controlled work area
• Appropriate PPE
• Communication between operations and intervention teams

The exact requirements depend on the pipeline, fluid, jurisdiction, project specification, and applicable standards.

How to Choose Between Hot Tap, Line Stop, and Stopple

A practical decision framework is:

If you primarily need to create a connection:

Consider hot tapping, subject to engineering assessment and suitability.

If you need temporary flow isolation:

Consider a line-stop system, subject to the required intervention design.

If you need specialized temporary sectional isolation:

Consider a stopple system, particularly where the project requires engineered isolation of an operating pipeline section.

If you need both access and isolation:

A combined intervention strategy may use:

Hot Tap + Valve + Line Stop/Stopple

The final selection should be based on engineering requirements rather than terminology alone.

Why Equipment Selection Matters

A pipeline intervention system should be treated as a complete engineered solution.

Important equipment categories can include:

• Hot tapping machines
• Line-stop machines
• Stopple machines
• Hot-tap fittings
• Isolation valves
• Temporary bypass systems
• Pressure-control equipment
• Stopping heads
• Hydraulic or mechanical actuation systems
• Monitoring instruments
• Pipeline cutting equipment

The equipment must be compatible with the pipeline dimensions and operating conditions for the intended application.

Pipeline Tie-In Equipment from SSEGPL

SSEGPL supplies equipment for pipeline construction, fabrication, welding, handling, and related pipeline applications.

For specialized pipeline intervention projects, equipment selection should be based on the actual application rather than a generic pipe-size requirement.

When discussing a pipeline tie-in equipment requirement, buyers should provide:

• Pipe diameter
• Wall thickness
• Material
• Operating pressure
• Operating temperature
• Fluid/service
• Required connection size
• Required isolation arrangement
• Field or workshop application
• Project requirements

This information allows the equipment supplier and responsible engineering team to determine the appropriate equipment configuration.

Conclusion

Hot tapping, line stopping, and stopple isolation serve different functions within pipeline modification and tie-in work.

Hot tapping is primarily used to establish access or a connection to an operating pipeline.

Line stopping is primarily used to establish temporary isolation within a pipeline.

Stopple systems provide a specialized approach to temporary pipeline isolation and can be part of complex intervention projects.

In many real-world projects, these methods are combined rather than selected as completely separate alternatives.

The correct choice depends on the pipeline’s diameter, wall thickness, material, fluid, pressure, temperature, integrity condition, required isolation, bypass requirements, and project objectives.

For pipeline contractors and operators, the most important principle is to begin with the pipeline operating conditions and engineering requirements, then select the intervention method and equipment that can satisfy those requirements through an approved and properly controlled procedure.

Frequently Asked Questions