Internal vs External Pressure Vessel Inspections

What external inspection can establish

An external examination can identify accessible evidence such as surface corrosion, leakage, distortion and deterioration around supports or connections. It can also reveal changes in installation or service conditions that warrant a closer review. Insulation, coatings, guards and nearby structures can restrict the view.

A sound-looking exterior does not establish the condition of the inside surface. Localised internal attack, deposits and damage concealed beneath insulation require a considered examination strategy. Record which surfaces were visible and which conclusions rely on other evidence.

What internal inspection adds

Internal examination provides access to surfaces and features not visible from outside, including areas affected by internal contents or deposits. Its value depends on preparation, cleanliness, lighting and access. Opening a vessel is not equivalent to examining every internal feature.

Entry and preparation must be managed under the site’s competent safety arrangements. Inspection planning is not an entry procedure. Some vessels cannot be entered or adequately viewed, so alternative evidence may need engineering review rather than an informal declaration that an internal inspection is unnecessary.

When comparing access options, scope pressure vessel inspections around the surfaces and damage mechanisms that need examination.

Choose around damage mechanisms

Ask where deterioration is credible and what evidence would detect it. General wall thinning, local pitting and cracking are different questions. A few external thickness readings may support one question while leaving another unanswered. A method should be selected for the mechanism, material, geometry and access.

Where an alternative to internal examination is being considered, establish its technical basis, coverage and limitations with competent personnel. Operational convenience alone does not demonstrate equivalence. The applicable inspection framework and jurisdictional context still need to be considered.

• Which surfaces and connections are of concern?
• Can preparation expose the areas that matter?
• What NDT coverage is needed to supplement visual examination?
• What remains uncertain after the proposed work?

Make the comparison useful for shutdown planning

Separate tasks that can be completed while equipment remains installed from those requiring opening, cleaning or removal of obstructions. Agree who provides each enabling task and how newly found damage will be escalated. This prevents a nominal inspection booking from becoming an unplanned outage without a decision-maker available.