On-Line Leak Sealing

Composite Repair

Brownfield Reality: How Leaks Become “Uncharacterized”

In new construction, we expect clean drawings, known materials, and controlled geometry. Brownfield work is different. Over a long service life, systems evolve in ways that are not always documented:

• Modifications and tie-ins change load paths and stress distributions
• Corrosion under insulation (CUI) removes wall thickness in unpredictable ways
• Unrecorded welds or patches create local stiffness changes and stress raisers
• Old leak clamps are welded over, extended, or simply left in place for an extended period, turning them into non-standard pipeline sections

When a leak appears on such a component, engineers is often working with limited visual access and partial wall thickness data. The challenge is not just to stop the leak, but to re-establish a load path around the defect that may not be visible

Reading the Leak from the Outside

Since the defect itself is often inaccessible, we rely on external inputs to try and define the problem, such as surface temperature patterns from contact or infrared measurements and localized wetting, staining, or insulation damage. These observations don’t explain the exact shape of the defect, but they are enough to estimate whether the medium is liquid, vapor, or mixed, gauge the likely severity of the leak, and identify critical regions around the area.

Additionally, more accurate Non-Destructive Testing (NDT) methods can be used such as, Ultrasonic Testing (UT) and Radiographic Testing (RT) which can reveal defects, their locations, and general shape.

From there, we define a working set of design conditions that the TLSD must contain. The goal is not to perfectly reconstruct the defect, but to define a design window for the enclosure and its materials.

Defining the Design Envelope

Once reasonable bounds on pressure, temperature, and medium are established, we focus on the TLSD itself. We treat the TLSD as a temporary pressure-retaining component, and design it to recognized pressure equipment standards:

• ASME Boiler and Pressure Vessel Code (BPVC) Section VIII, Division 1
• Applicable local pressure vessel standards
• Local health and safety codes and regulations

These codes provide the rules and formulae for:

• Allowable stresses
• Required wall and shell thickness
• Flange and bolt design
• Local reinforcement for openings
• Any additional local design rules impose by regional pressure equipment legislation

Rather than guessing what the defect looks like internally, we design the TLSD to safely withstand a defined maximum pressure and temperature, using stress limits and safety factors.

Mechanical Engineering of the TLSD

With the design envelope set, the TLSD is engineered much like a small, custom pressure vessel.

Key mechanical checks include:

• Hoop and longitudinal stress calculations for the TLSD shell
• Wall and shell thicknesses, including the corrosion allowance
• Bolt load calculations to ensure correct bolt size, quantity, and spacing
• Gasket or sealing groove compression to maintain contact without overstressing
• Bending and shear stresses in the enclosure body, flanges, and shells
• Axial constraints, particularly where net thrust is present due to different pressure areas on an enclosure
• Local reinforcement around injection ports, threaded connections, and vent paths
• In many cases, these checks can be performed using standard BPVC / ASME Section VIII Division 1 methods.

Finite Element Analysis (FEA) is introduced when:

• The geometry is too irregular for code formulas to apply cleanly, or
• Load paths around existing clamps or complex fittings are not intuitive

FEA then becomes a tool to confirm that the TLSD will distribute loads safely around the defect and any legacy hardware.

Practical Design Principles for Uncharacterized Leaks

Beyond the calculations, we must apply a few core design habits that consistently improve outcomes in uncertain situations.

Conservative Design

Due to the uncertainties that exist, the TLSD is designed for higher-than-expected loads.

That typically means:

• Pressure design values above normal operating pressure
• Temperature assumptions that match the highest credible line condition
• Material strength taken from code-allowable values at this temperature

The intention is to provide a solution that remains structurally sound even if the real conditions sit at the top of the anticipated range.

Fitments: Undersize, Measure, Machine

In the field, landing areas are rarely perfectly round:

• Oval pipes
• Irregular clamp surfaces
• Local wall loss

To deal with this, TLSD components are typically:

• Manufactured with undersized bores, then
• Machined on-site to match measured dimensions, in addition to
• Caulking lips to compensate for irregular clamp surfaces

This approach is especially valuable where landing surfaces are non-circular or uncertain. It avoids excessive gaps and prevents local overstressing from point contacts.

Sealing Solutions

While the TLSD body handles pressure containment, the sealing system itself is built with added factors to ensure a tight seal:

• Primary seal: Injected compound forming the immediate pressure barrier
• Secondary seal: An additional sealing groove with compound packing or void filling
• Tertiary seal: Gland followers incorporating extra sealing grooves, also injectable

This layered approach improves reliability and offers options for future re-injection without redesigning the entire enclosure.

Materials That Can Handle Many Unknowns

When the defect is not well defined, the selected materials must be able to tolerate variability and uncertainty in service conditions: changes in medium, temperature, and environment, without rapid loss of performance.

Sealants

Beruseal uses sealants engineered for both varying chemical compatibility and wide temperature ranges, in addition to some unreactive services:

• Multi-environment resistance to hydrocarbons, water, amines, and steam etc.
• Stability from low temperatures up to high-temperature service (≈500°C and above, where applicable)

The compound is selected not just for the known medium, but for the realistic spectrum of what might be present or expected.

Bolting Materials

Bolts and nuts see high stresses and, in many cases, elevated temperatures. Typical material choices include:

• ASTM A193 Grade B7, B8, B8M studs
• Matching ASTM A194 nuts (e.g., Grade 2H, 8, 8M)

Selection is based on:

• Required tensile strength
• Service temperature
• Corrosion allowance

Correct bolting is a key part of ensuring the TLSD can be tightened, maintain preload, and resist separation forces over time.

Enclosure Materials

The enclosure shell and structural components are usually fabricated from:

• Carbon steel for general-purpose service
• Stainless steel where chemical or environmental corrosion risk is high
• Low-alloy steels for specific high-temperature or strength requirements

In all cases, a corrosion allowance is built into wall thickness calculations, aligned with code and expected exposure, to ensure the TLSD remains structurally sound over its intended service duration.

Safety by Design

The engineering side only works if the procedural side is equally strong.

Before any on-line work begins, a risk assessment is carried out to establish:

• Confirmed or assumed pressure ranges
• Temperature distribution in the area
• Worksite access and escape routes
• Isolation or depressurization options

Where applicable, TLSDs are designed with:

• Relief or vent provisions to avoid trapped pressure
• Clear plans for controlled venting or emergency depressurization

One rule governs everything: Do not exceed the known design limits of the line, the TLSD, or the materials. To formalize this, every TLSD design goes through:

• Sign-off by a Professional Engineer (Pr. Eng.) and in some cases for must higher risk projects independent review by a Design Verification Engineer

This makes sure that any creative problem-solving in the field remains grounded in formal engineering accountability.

Design Verification and Learning from the Field

Every TLSD design lives in two worlds: In calculations, where assumptions are made and checked and the field, where the device is installed, pressurized, and exposed to real conditions. When geometries are straightforward, BPVC / ASME Section VIII Division 1 methods are sufficient for verification. In more complex cases, FEA is brought in to visualize stress distributions and validate the chosen wall thicknesses, flanges, and bolt patterns.

After installation:

• Performance is monitored where practical
• Feedback is captured from inspections and follow-up visits

Over time, this turns “unknown” cases and uncharacterised leaks into problems with proven solutions.