Overview of Static Equipment Inspection

5. How to Interpret Inspection Results

Inspection results provide critical insights into the current condition of equipment and are essential for determining whether it is safe, reliable, and fit for continued service. Interpretation involves comparing actual findings against design criteria, industry codes, and operational requirements, while also considering long-term risk factors such as degradation mechanisms and operating environment.

Thickness Measurements

Wall thickness data obtained through ultrasonic testing (UT), radiographic testing (RT), or other NDE methods is compared with:

• Original design thickness – the as-built condition of the equipment.

• Minimum allowable thickness (tmin) – calculated using applicable codes (e.g., ASME, API).
  If the measured thickness approaches or falls below tmin, the equipment may no longer safely withstand design pressures. Engineers also evaluate localized thinning, uniform corrosion, and potential stress concentration areas. Predictive models may be used to estimate how quickly remaining thickness will be consumed.

Flaw Detection

Surface and subsurface defects detected by NDE methods (such as MT, PT, UT, or RT) are assessed for:

• Size and depth – small, shallow flaws may be tolerable, while larger or deeper flaws often require repair.

• Location – cracks near welds, nozzles, or high-stress regions pose greater risks than those in low-stress zones.

• Orientation – flaws aligned with principal stresses can propagate more rapidly.
  Acceptance criteria outlined in relevant standards guide whether equipment can remain in service, needs repair, or must be removed from operation.

Corrosion Assessment

Corrosion evaluations consider both the current extent of metal loss and the rate of deterioration over time. Key steps include:

• Comparing multiple inspection data points to establish corrosion trends.

• Estimating corrosion rates (mm/year) to forecast remaining life.

• Distinguishing between different corrosion mechanisms (uniform, pitting, MIC, galvanic).

• Identifying critical areas where localized corrosion could lead to sudden failure.
  This information supports remaining life calculations and the planning of proactive maintenance or replacement.

Leak and Pressure Test Results

Hydrostatic or pneumatic pressure tests provide a direct check of mechanical integrity. Key points in interpretation include:

• Presence of leaks – even small leaks indicate defects or weaknesses in welds, joints, or materials.

• Test pressure performance – equipment must sustain pressures above design operating levels without deformation or rupture.

• Post-test evaluation – re-inspection may be required to check for new cracks or distortions caused by the test itself.
  Failure during a pressure test is a critical finding requiring immediate investigation and corrective action.

Thermal Imaging Analysis

Infrared thermography reveals abnormal heat signatures on operating equipment. Interpretation focuses on:

• Hot spots – often caused by insulation damage, refractory failure, or fluid leaks.

• Uneven temperature distribution – may signal blockages, fouling, or internal flow restrictions.

• Connections and joints – abnormal heating can indicate loose or corroded bolting, flange leaks, or electrical faults.
  Thermal imaging is especially valuable for detecting issues without requiring shutdown.

Risk-Based Evaluation

Inspection results are most powerful when integrated into a risk-based inspection (RBI) framework, where both probability and consequence of failure are evaluated. Interpretation includes:

• Ranking equipment by criticality to prioritize inspection and maintenance.

• Identifying high-risk components requiring closer monitoring.

• Balancing inspection intervals with acceptable risk levels.

• Supporting decision-making for repair, replacement, or continued service.
  By combining condition data with risk assessment, companies can optimize inspection resources and maintain safety while reducing unnecessary downtime.