Hot tapping is the creation of a branch connection on a pressurized, in service pipe or vessel without shutting the system down and without draining it. A fitting with an isolation valve is attached, usually welded, and the wall is drilled under full operating pressure. The severed section, the coupon, is safely retained. The plant stays in production.

Is hot tapping safe during operation?

Hot tapping is an established procedure, but it is a live intervention on an active pressure boundary. Safety does not depend on the drilling itself, it depends on the decision before it. Wall condition, weldability of the actual base metal, sufficient flow for heat dissipation, the medium and its ignitability, and personnel exposure decide go or no go. FRALEX GLSC structures exactly that decision.

Which standards apply to hot tapping?

The practice relevant references are API 2201 (Safe Hot Tapping Practices) and ASME PCC-2, Article 2.11 (Hot Tapping and In Service Welding). The design frame of the line comes from construction codes such as ASME B31.3 or EN 13480. These standards describe how to execute a tap on a sound component. Whether the specific aged line qualifies in its actual condition is not answered conclusively by any of them.

What is the minimum wall thickness for in service welding?

There is no universal limit. What matters is the remaining, actually measured wall thickness in the weld area, not the nominal value. If the remaining thickness is too low, the risk of burn through rises because the heat is not safely dissipated. API 2201 and ASME PCC-2 therefore require a condition assessment and a qualified in service welding procedure with limited heat input. The value is always object specific.

What is the difference between hot tapping and line stopping?

Hot tapping creates a connection. Line stopping uses such a tap to temporarily isolate the flow, for example to work downstream without shutting the whole plant. Hot tapping is often the first step, line stopping the second one built on it. Both are live interventions on the pressure boundary.

When is hot tapping not permissible?

It becomes critical with insufficient remaining wall thickness, materials with poor weldability, missing or unstable flow for heat dissipation, media with high ignition or reaction risk, and an unclear documentation basis. In such cases the real deliverable is not the tap, it is the justified no go. That judgment is exactly what FRALEX captures.

GLSC // Global Leak Sealing Code

Hot Tapping

Creating a branch on a line that is under pressure and stays in production. Technically well controlled and established for decades. And still one of the interventions where the real failure does not start at the drill, but in the decision before it.

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Author Frank Havemann25 years of field experiencearound 6.000 accompanied interventions

Definition

What hot tapping is

In hot tapping, a fitting with an isolation valve is applied to a pressurized, in service line, usually welded, in some cases clamped. The wall is then drilled under full operating pressure with a dedicated machine. The severed piece of material, the coupon, is safely retained. The valve stays in place as a permanent connection.

The purpose is stated simply: create a new connection without shutting the plant down and without draining the system. No standstill, no production loss, no major shutdown. This is where the commercial appeal comes from, and this is where the risk comes from that the construction codes do not capture.

The grey zone

Where the codes end

Construction codes such as ASME B31.3 or EN 13480 describe how a line is designed and built. Procedure standards such as API 2201 and ASME PCC-2, Article 2.11, describe how a tap on a suitable component is executed cleanly. Both assume an intact, specification compliant starting condition.

On site, however, the fresh line from the datasheet is rarely what you face. You face a line that has been in service for ten, twenty or thirty years, with real wall loss, a welding history, and a medium that has changed the material. The question is then no longer how to tap. The question is whether this specific component qualifies at all in its actual condition.

None of these standards answers that question conclusively. It sits between manufacturing code and operational responsibility. This is the liability vacuum that FRALEX closes systematically. Not with a new material, but with a traceable decision.

Decision logic

The six questions before the tap

FRALEX GLSC turns the experienced technician gut feeling into a testable structure. Before every hot tap there are six questions whose answers are documented and owned.

1. Remaining wall thickness

Not the nominal value counts, but the actually measured wall thickness in the planned weld and drill area. Too little remaining thickness means the welding heat is not safely dissipated into material and medium. The result is burn through, an uncontrolled release exactly where the work is happening.

2. Weldability of the actual base metal

The material on the datasheet and the material after years in the medium are not the same. Carbon equivalent, embrittlement and hydrogen cracking decide whether an in service weld is permissible at all. This assessment needs a qualified procedure, not routine.

3. Flow and heat dissipation

A stable flow carries the introduced heat away and protects against burn through. If the medium is static or the flow is unstable, the entire risk picture shifts. In certain configurations, the absence of flow alone is a reason for a no go.

4. Medium and ignitability

Composition, ignition temperature, reactivity and possible deposits determine which procedures are permissible and which protective measures become mandatory. A flammable or reactive medium shifts the line between acceptable and irresponsible significantly.

5. Personnel exposure

Who stands where when the wall is breached. The live intervention takes place on an active pressure boundary. Assessing personnel exposure is part of the decision, not an appendix after it.

6. Documentation and liability

Whoever owns a live intervention must be able to justify it afterwards. If the reliable basis for the condition is missing, the basis for the release is missing. A cleanly documented no go is legally stronger than an undocumented go that happened to work out.

Normative frame

The relevant reference documents

API 2201Safe Hot Tapping Practices. Procedure and safety requirements

ASME PCC-2, Art. 2.11Hot Tapping and In Service Welding. Repair and tapping on pressure equipment

ASME B31.3Process Piping. Design frame of the process line

EN 13480Metallic industrial piping. European design frame

API 570Piping Inspection Code. Condition assessment of in service lines

FRALEX GLSCThe decision layer above them. Go or no go in the actual condition

The first five rows say how to build, inspect and tap. The last row says whether you may do it here and now. Integrity is a decision, not a material property.

FAQ

Common questions

Short, reliable answers to the questions that come up before every hot tap. For the full logic: the GLSC in the Veritas Library.

Creating a branch on a pressurized, in service line without shutdown and without draining. A fitting with an isolation valve is applied and the wall is drilled under pressure, the severed piece safely retained.

Established yes, but it remains a live intervention on an active pressure boundary. Safety depends on the decision before it: wall condition, weldability, flow, medium and personnel exposure. FRALEX GLSC structures exactly that decision.

The practice relevant references are API 2201 and ASME PCC-2, Article 2.11. The design frame comes from ASME B31.3 or EN 13480. They describe execution on a suitable component, not whether the aged line qualifies in its actual condition.

There is no universal limit. What matters is the actually measured remaining wall thickness in the weld area. Too little material means burn through risk because the heat is not dissipated. The standards therefore require condition assessment and a qualified procedure with limited heat input.

Hot tapping creates the connection. Line stopping uses that tap to temporarily isolate the flow. Hot tapping is often the first step, line stopping the second. Both are live interventions on the pressure boundary.

With insufficient remaining wall thickness, poor weldability, missing or unstable flow, high ignition or reaction risk of the medium, or unclear documentation. Then the real deliverable is the justified no go.