Vapor is leaking from a broken shell-flange gasket when the vessel is heated, and the proposed repair is to weld a plate inside the vessel across the flange gap. The stated design condition is 25 kPa at 150°C; those values do not by themselves make an improvised weld repair safe or code-compliant.
What does the vapor leak tell you about the joint?
A gasketed flange seals by compressing a compatible gasket between suitably aligned sealing faces. A leak means that the joint no longer maintains an effective seal under its actual conditions. A visibly broken gasket is a finding, not necessarily the root cause: replacing it without correcting the cause can lead to another leak.
The discussion raises possible concerns about bolt size, gasket width, flange stiffness, flange rotation, face flatness, and joint assembly. The drawing and dimensions are not sufficiently clear to treat those observations as confirmed design defects. Check the vessel drawings and measure the actual joint before drawing conclusions.
| What you observe | Possible cause to investigate | What to check |
|---|---|---|
| Gasket is broken or damaged | Incorrect gasket selection, installation damage, uneven compression, or joint movement | Removed gasket condition, material compatibility, dimensions, and installation record |
| Leak appears during heating | Thermal expansion or temperature-dependent changes in the joint or gasket | Leak behavior during the heat-up cycle, joint alignment, and process conditions |
| Uneven gasket contact or repeat leakage | Uneven bolt loading, flange misalignment, face damage, or flange rotation | Sealing-face condition and flatness, bolt condition, tightening sequence, and flange geometry |
| Bolting or flange dimensions appear marginal | Insufficient joint capacity may be possible, but visual estimates are not a design check | Design documents, measured dimensions, bolt specifications, gasket supplier input, and engineering review |
Separate a gasket or joint problem from a vessel-boundary defect. Inspect the gasket seating faces, shell flange, welds, and adjacent shell for damage or deformation. Have a qualified vessel engineer determine whether the leak originates only at the gasket joint or whether the pressure boundary itself is compromised. Check before proceeding: identify the leak location and document the actual joint and damage.
Why is an internal plate weld not a routine gasket repair?
The proposed plate would change the vessel’s pressure-retaining construction rather than restore the original gasketed joint. Even at a stated design pressure of 25 kPa, the vessel remains a pressure-containing system operating at a stated design temperature of 150°C. Pressure, temperature, contents, geometry, material, and applicable construction requirements all affect whether a repair is acceptable.
A weld can introduce heat, shrinkage, residual stress, local distortion, and material compatibility problems. Distortion may affect the flange faces or shell; the repair can also make future inspection or gasket replacement more difficult. Welding from inside the vessel also requires the vessel to be taken out of service and prepared under approved hot-work and confined-space controls. Do not weld over a live, pressurized, hot, or inadequately cleaned vessel.
Calling a weld a “seal weld” does not make it an approved pressure-boundary repair. Its acceptability depends on the vessel’s construction requirements and an engineered repair plan. The field report specifically cautions that the construction code must be checked; a low pressure or a temporary label is not a substitute for that review.
Check before proceeding: confirm the vessel’s construction documentation, material, service, and repair requirements with the responsible vessel engineer and site authority. If that review does not authorize the proposed weld repair, do not perform it.
How should you decide whether the service permits temporary containment?
First identify the vessel contents and the consequences of release. The discussion distinguishes water or steam service from hydrocarbon service and notes that a temporary enclosure may be unacceptable for hydrocarbons. That is a warning to make a service-specific risk decision, not a blanket approval for water or steam. Vapors can be hazardous even when the liquid contents are not; assess toxicity, flammability, exposure, ignition, and environmental consequences using the site’s process-safety procedures.
Do not use epoxy, high-temperature RTV, or a commercial leak-sealing enclosure as an informal substitute for an engineered repair. These approaches were suggested in the discussion, but no product, temperature rating, chemical compatibility, pressure rating, or acceptance criteria were established. A sealant that appears to stop a leak may conceal deterioration without restoring a verifiable pressure boundary.
Compare options with the responsible engineer and operations team:
| Option | Decision basis | Key limitation |
|---|---|---|
| Isolate and replace the gasket | Preferred when the joint can be safely dismantled and the flange remains serviceable | Requires resolving access and shutdown constraints, plus correcting the cause of failure |
| Engineered temporary leak-containment system | Consider only when designed, rated, installed, and approved for this service and condition | Service compatibility and acceptance must be confirmed; a generic “temporary box” is not a universal solution |
| Welded repair | Use only under a reviewed repair plan that meets applicable vessel requirements | Requires qualified engineering, materials, welding controls, inspection, and acceptance |
| Unspecified adhesive or sealant | No basis for acceptance from the information given | Product suitability and pressure-boundary integrity are unverified |
Check before proceeding: record the contents, operating state, release hazards, and approved temporary-control decision. If service suitability or approval is unresolved, isolate the vessel and do not improvise a seal.
How do you investigate the gasket and flange before replacement?
Use a controlled shutdown and the site’s isolation, depressurization, cooling, draining, cleaning, and access procedures. A vessel opened for inspection may still contain hazardous residues or an unsafe atmosphere; follow the applicable confined-space and hot-work controls. Do not infer that it is safe because the process pressure is low.
- Review the vessel drawings, joint details, gasket specification, bolt specification, and available maintenance records.
- After safe isolation and opening, inspect the removed gasket for cracking, extrusion, uneven compression, chemical attack, or other damage. Record the failure pattern before discarding it.
- Inspect and measure the sealing faces, alignment, flange condition, and adjacent welds or shell. Check for distortion, damage, corrosion, or evidence of uneven contact.
- Verify bolt material and condition, gasket dimensions and material, and the actual assembly method. Have the gasket supplier and vessel engineer review selection and joint requirements where needed.
- Compare measured construction with approved design information. Treat comments about 3/4-inch bolts, a 40 mm flange, or an overly wide gasket as items to verify, not established facts about this vessel.
Torque alone does not prove a sound joint: the required joint load depends on the design, gasket, bolting, condition, and assembly procedure. Use the approved tightening method and sequence for the joint rather than increasing bolt load by guesswork; excessive load can damage the gasket, bolts, or flange.
Check before proceeding: resolve whether the joint can be returned to service with a correctly selected gasket and controlled assembly, or whether the flange or pressure boundary needs repair.
Which repair path should you approve?
If the inspection confirms a serviceable flange and the problem is limited to the gasket, replace the gasket with a suitable material and dimensions selected for the service. Correct the cause of failure, then assemble the joint using the approved procedure. This preserves the intended joint design and avoids introducing an unreviewed weld.
If the joint cannot be dismantled promptly, refer the case to the vessel engineer and site integrity authority for an approved temporary repair or operating disposition. They must evaluate the actual contents, conditions, geometry, materials, and construction requirements. A temporary containment system may be an option only when its suitability and installation are approved. If a weld repair is proposed, obtain an engineered repair plan that addresses materials, welding, inspection, and acceptance before any work begins.
Do not authorize an internal plate weld merely because the vessel is intended for replacement later. Until the replacement is installed, the existing vessel must remain within an approved safe operating condition. If the leak cannot be controlled under an approved plan, keep the vessel out of service.
Check before proceeding: obtain a documented repair or operating disposition identifying the responsible approver and required inspection and acceptance criteria.
How do you verify the repair before returning the vessel to service?
Follow the approved repair and commissioning plan; do not invent a test pressure or test method. The responsible engineer must specify the acceptance criteria in accordance with the vessel’s construction and repair requirements. Verify that the repaired joint or pressure boundary has passed the specified examination or test and that there is no leakage at the approved conditions.
- Confirm the work matches the approved repair plan and that required inspections and records are complete.
- Verify the gasket or repair materials, joint assembly, and any specified examination or pressure test meet their documented acceptance criteria.
- Return the vessel to service only through the approved startup sequence, monitoring the joint for leakage as process conditions change.
- Record the repair, inspection results, operating conditions, and any follow-up actions. If leakage recurs, isolate the vessel and reopen the root-cause investigation rather than adding sealant or weld metal.
End-to-end check: confirm documented acceptance, start the vessel under the approved procedure, and verify the flange remains leak-free at the specified operating conditions.
FAQ
Can I weld a plate over a leaking vessel flange?
Not as an improvised repair. The vessel engineer must review the construction requirements, service, materials, and repair plan and approve the work before welding.
Does 25 kPa make a temporary weld repair safe?
No. The stated design condition is 25 kPa at 150°C, but pressure alone does not establish repair acceptability. Contents, temperature, vessel construction, and repair requirements also matter.
How do I find the cause of a broken flange gasket?
Inspect the removed gasket and sealing faces, measure alignment and flange condition, and review gasket and bolt specifications and assembly records. Investigate uneven loading, damage, compatibility, and heat-related joint movement.
Can I use RTV or epoxy to stop a vessel flange leak?
Do not rely on unspecified sealant as a pressure-boundary repair. Confirm any proposed product’s service suitability and obtain engineering and site approval for the containment method.
How do I verify the vessel repair before startup?
Complete the inspections and test specified in the approved repair plan, verify the documented acceptance criteria, then start under the approved procedure and check for leakage at the specified operating conditions.