Pressure Vessel CUI Inspection: Plan Exposure Before UT
Plan pressure-vessel CUI inspection in Australia: select insulation openings, verify exposed-wall UT and record areas still unexamined.
PetroBot Technologies ·
English technical guide for asset-integrity and industrial-inspection professionals in Australia.
For insulated vessel work packs in Australia, tie each opening to a water-entry clue, qualify exposed-wall UT and carry unopened bands into the handoff.
Direct answer
For pressure-vessel CUI inspection, choose insulation openings from the vessel's material, service, coating, wetting history and the integrity decision. Photograph the jacket and insulation before removal. Examine the revealed coating and steel, then accept thickness readings only where the approved procedure gives a valid response at a mapped location. MagRover can collect visual and UT data on a suitable exposed ferromagnetic route after adhesion, access, coupling and recovery checks. Show unopened, obstructed and rejected locations on the gap map, with a named follow-up method or owner decision.
Technical sources: API RP 583 — Corrosion Under Insulation and Fireproofing scope, AMPP — Understanding Corrosion Under Insulation, PetroBot — Pressure Vessel Inspection and additional references.
Key takeaways
- Tie each proposed opening to a named vessel zone, credible water-entry path and inspection decision.
- Photograph jacket and insulation as found; a stain or failed seal is a clue, not a wall-thickness result.
- Map exposed coating and steel before cleaning, then record every change made for examination.
- Accept UT only where the approved procedure produces a repeatable response on the actual surface and geometry.
- Carry unopened insulation, rejected readings and physical obstructions into the gap map.
- Assign engineering disposition, coating repair and weatherproof reinstatement before the work pack closes.
What decision must this CUI inspection support?
A crew finds a low value in a patch beside a failed nozzle seal. The shell below the seam is still jacketed. Define whether the result calls for more exposure, repair or an engineering review, then name the area and evidence needed for that decision.
Start with the controlled vessel ID and drawing revision. Confirm material, design and nominal-thickness records, current and past service, operating temperature, coating and insulation system, earlier CUI findings, repairs, leaks and wetting history. Identify the owner-adopted inspection basis and the authorized inspector and engineering roles. API 510 covers in-service vessel inspection, rating, repair and alteration; API RP 572 addresses vessel inspection practice. Those documents frame the program, while the owner's adopted requirements govern this asset.
Fix a coordinate convention before insulation comes off: a permanent axial datum, distance along the shell, a declared circumferential zero and direction, and named head, nozzle and support zones. Photograph and label an attempted point against that convention even if its UT response is later rejected. A nearby good value never silently replaces the planned location.
Why a bare spot cannot clear an insulated vessel
Contact UT measures only where the qualified probe has access and a valid back-wall response. Suppose an opening exposes the shell above a saddle. The accepted points describe that exposed patch. They do not measure the jacketed strip below it, the head transition or the steel behind a nozzle pad. Keep those zones separate on the map.
A dry-looking opening is equally local. Water can enter at another penetration, move within an insulation system and remain out of sight. Describe what the opened area showed; leave the adjacent closed surface as unopened insulation. Widen the exposure or specify another validated method when the integrity decision needs evidence there.
Read the jacket before removal
Survey the accessible jacket on the shell and heads before anyone disturbs the weather barrier. Record open laps, failed sealant, loose bands, punctures, wet or displaced insulation, staining below seams, and changes around nozzles, clips, supports and terminations. Give each photograph a vessel coordinate and viewing direction; mark jacket areas the crew could not reach.
Moisture can enter through damaged jacketing and stay concealed. A stain gives the team a place to investigate, not a wall-thickness result. Record how each clue changes the opening priority without calling it proof of corrosion.
How should the team choose where to open?
Use the owner's CUI assessment to combine material and service, insulation and coating design, wetting history, earlier findings, jacket condition, geometry and consequence. API RP 583 addresses inspection and mitigation of CUI on pressure vessels, among other assets. Choose each opening around a question whose answer could change the next decision.
Mark the proposed opening limits on a controlled drawing and in field photographs. Include a comparison area only when it helps answer a defined question. If an opening reveals damage reaching its edge, the qualified inspection plan needs an expansion rule; the original small patch cannot stand in for the surrounding covered wall.
| Field clue or history | Opening question | Evidence to collect | Still unknown afterward |
|---|---|---|---|
| Failed nozzle seal | Did water reach the shell at this penetration? | As-found insulation, coating and metal views; valid exposed-wall UT | Condition beneath the neighboring jacket. |
| Stain below a jacket lap | Does the wetting path continue down the shell? | Located views along the opened path and accepted readings where needed | Wall outside the opened path. |
| Earlier local CUI | Has the known affected area changed or extended? | Revisit matched coordinates and examine exposed boundaries | Unopened extensions and unmatched historical points. |
| Head or support transition | Can the chosen method reach the geometry? | Documented access trial and a separate technique decision | Steel behind pads, supports or closed insulation. |
Define the exposure and restore plan
Agree the operating state, permits, isolation and area controls with the site before removal. Confirm insulation materials and handling precautions, safe access, weather protection, marking method, surface-preparation limits and where removed material will go. A live vessel can impose temperature and process restrictions that change both exposure and UT technique.
Before a crawler trial, confirm that the configured equipment is permitted in the work area. Route the tether clear of hot surfaces and pinch points, control the area below the run and agree how the crew will retrieve the crawler if adhesion or communication fails. Record any jacket or metal the crew cannot safely reach as an access gap.
Assign who photographs the jacket before cutting, the insulation layers during removal and the steel before cleaning. Name who will assess coating damage, repair it, reinstate insulation and seal the weather barrier. Reinstatement is part of the inspection handoff: an open or poorly restored jacket creates a new water-entry path.
Set hold points for unexpected leakage, suspect deep loss, damaged supports or any condition outside the planned scope. The site and owner-authorized roles control work and disposition. PetroBot's role is the bounded inspection acquisition agreed for suitable access.
What should be recorded on the revealed metal?
Record the opening boundary and insulation condition first. Photograph coating color, blistering, disbondment, deposits, staining, visible pits and exposed steel before wiping or grinding changes the surface. Tie each view to the vessel datum and document physical scale in the field record.
After the as-found record, prepare only the area and finish required by the approved visual or UT procedure. Log what was cleaned, where coating was removed and which features remain obscured. A visible pit is an observation; a valid UT value is a measurement. Neither alone assigns the corrosion mechanism or the remaining-life decision.
Compare previous photographs and thickness data only when the location, surface, setup and repair history can be matched. The same general area on a drawing is not necessarily the same measurement point.
Where can MagRover fit?
MagRover supports visual and UT acquisition on accessible, prepared ferromagnetic vessel surfaces. For this job, first remove the insulation along a proposed route and confirm that the exposed shell or head is suitable. Demonstrate magnetic adhesion, stable travel, obstacle clearance, probe seating, coupling, position tie-in, tether behavior and recovery on representative geometry before crediting a run.
A camera view records visible condition. A contact-UT result requires its own accepted response. Robot travel alone establishes neither UT coverage nor the condition behind unopened insulation. If the route fails a trial, retain the planned locations and hand them to another qualified method or access plan.
| Route feature | Demonstrate before acquisition | If it fails |
|---|---|---|
| Material and coating | Adhesion on the actual prepared ferromagnetic surface | Use a qualified non-robotic access or method. |
| Curved shell or head | Stable travel, probe seating and repeatable response | Reposition, change technique or leave the point rejected. |
| Nozzle, pad or support | Clearance and recoverable path around the feature | Map the obstacle and examine it separately. |
| Opening edge | Enough exposed route for controlled entry, exit and location tie-in | Revise the exposure with the owner or use another method. |
What makes each UT result usable?
The approved procedure controls material velocity, equipment checks, calibration or verification, surface condition, coating treatment, couplant, temperature, curvature, probe seating, signal quality and recording. At the actual test location, obtain a resolved, repeatable back-wall response. Record an unstable signal or no response as rejected, with the location and reason, rather than replacing it with the nearest convenient value.
ASTM E797/E797M-21 is a manual pulse-echo contact practice, mainly for flat, parallel material. Its scope limits use on non-parallel or concentric geometry and at temperatures above 93 °C. It cannot qualify a robotic route on this vessel. ISO 16809:2025 covers ultrasonic thickness determination; ISO 16831:2025 covers thickness-equipment verification. Demonstrate the approved robotic procedure on representative vessel geometry and conditions.
A thin indication deserves a method check before interpretation: confirm the setup and location, examine the response, then expand the mapped examination as the qualified procedure directs. Keep the initial signal and any rejected attempt in the record.
Treat nozzles, welds and obstacles separately
A nozzle neck, reinforcement pad, clip, saddle and head-to-shell transition changes the surface and the available route. Give each feature its own coordinate and technique decision. Do not interpolate a valid shell point through a pad, weld, jacket remnant or shadowed area to manufacture coverage.
Ordinary thickness UT does not resolve crack-like concerns. If the vessel damage review calls for weld or cracking examination, the owner specifies a qualified method and personnel for that mechanism. Keep that examination separate from the CUI thickness map.
How should credible wall loss be confirmed and expanded?
When a value is low or a response is inconsistent, stop treating the first number as settled. Recheck the probe setup, coupling, surface and back-wall signal at the original coordinate. Keep both the initial and confirmation records. If the condition is credible, map its exposed extent using the owner-approved procedure and expand the opening when the boundary remains unresolved.
Join the accepted thickness map with the as-found coating and metal photographs, service and repair history, and any other qualified examination. A thickness value cannot, by itself, tell which wall face lost metal. The authorized inspector and engineer decide inspection density, minimum acceptable thickness, further access, repair and continued service under the vessel's adopted program.
State what remains unexamined
Use separate evidence states on the final drawing: planned; jacket or insulation visual only; exposed metal visually examined; valid UT point or scan segment; attempted UT rejected; physically blocked; unopened insulation; complementary method pending; and engineering disposition pending. Show the opening outline and each valid result's actual location. A continuous crawler path is not a continuous band of accepted UT.
If the owner uses a through-insulation screening method, qualify it for this vessel, damage form and geometry. Show its footprint and blind spots separately from the exposed-wall UT map. Use the result to choose the next opening only within that method's demonstrated limits.
The gap map should answer a practical question: if the decision depends on the unopened lower shell, who will expose it, examine it by another qualified method or carry the uncertainty into the owner review? A blank area on the drawing is not an acceptable substitute for that answer.
What belongs in the CUI handoff?
Close the pack with the controlled asset and drawing revision, inspection decision, CUI risk rationale, coordinate convention, opening boundaries, before-and-after photographs, surface preparation, accepted and rejected UT with method settings, physical obstacles, unopened bands and any complementary-method results. Keep the coating repair and insulation reinstatement record with the same locations.
Name the owner for every unresolved zone and every engineering decision. The inspector should be able to point to a nozzle or jacket seam on the drawing, follow the as-found photographs to the exposed steel, see which readings were accepted, and tell where the evidence stops. The next opening or method then has a clear owner and reason.
Risk clue
Locate wetting history, jacket condition and the question it raises.
Planned opening
Mark the boundary and owner-approved access on the vessel drawing.
As-found record
Photograph jacket, insulation, coating and steel before changing them.
UT decision
Accept a procedure-valid response or record the attempt as rejected.
Remaining gap
Name unopened, blocked and unresolved surfaces.
Owner action
Assign further examination, repair, reinstatement and disposition.
Frequently asked questions
Can contact UT inspect a pressure vessel through intact insulation?
The planned MagRover contact-UT workflow needs a suitable exposed and prepared metal route. For covered steel, the owner must expose it or specify a separately validated method with its own coverage limits.
Which vessel insulation areas should be opened first?
Use the owner's CUI plan, material and service history, jacket condition, water-entry details, earlier findings and the decision the inspection must support. Mark each proposed opening and its purpose on a controlled vessel drawing.
Does a dry-looking jacket rule out CUI?
No. Record the jacket as found, but its appearance does not establish the condition of the steel beneath it. Keep unopened areas on the gap map.
Can a MagRover reading represent the unopened band beside it?
No. Credit mapped, procedure-valid readings only on the exposed route actually examined. The adjacent jacketed band remains unexamined unless another validated method covers it.
What should happen when a low or unstable reading appears?
Check setup and back-wall response at the original coordinate, preserve the first attempt, and expand examination under the approved procedure when the result is credible. Send the mapped evidence to the owner-authorized inspector and engineer.
Who decides whether the vessel can remain in service?
The owner-authorized inspector and engineering roles apply the vessel's inspection basis, design and service information, and any needed assessment. PetroBot supplies the agreed inspection evidence.
Technical references
- API RP 583 — Corrosion Under Insulation and Fireproofing scope
- AMPP — Understanding Corrosion Under Insulation
- PetroBot — Pressure Vessel Inspection
- PetroBot — MagRover
- API 510 — Pressure Vessel Inspection Code
- API RP 572 — Inspection Practices for Pressure Vessels
- ASTM E797/E797M-21 — Manual Ultrasonic Pulse-Echo Contact Method
- ISO 16809:2025 — Ultrasonic Thickness Determination
- ISO 16831:2025 — Verification of Ultrasonic Thickness Equipment
- HSE — Inspection and Non-Destructive Testing
Show the opening plan before booking the crawler
Share the vessel ID and drawing, material, service and temperature, insulation and coating type, nozzle and support layout, prior CUI or UT records, suspected water-entry locations, proposed openings, surface preparation, access and area controls, and the decision the evidence must support. PetroBot can review whether an exposed ferromagnetic route suits MagRover visual and UT acquisition and where another method or access plan is needed.