Defensible High-Temperature Analysis Workflow

The need for a structured workflow

High-temperature structural analysis is a complex, multi-step process that involves thermal analysis, structural analysis, creep constitutive modelling, life prediction and uncertainty quantification. Each step depends on the previous ones, and an error or a shortcut at any step can invalidate the entire analysis. A structured workflow ensures that all the necessary steps are performed, that the dependencies are respected, and that the analysis is defensible — meaning that the results can be traced, verified and justified. The workflow presented here is a 15-step process that covers the full scope of a high-temperature analysis, from the requirements through to the final report. The steps are sequential, but some may be iterative (e.g. the material data may need to be supplemented if the initial data is inadequate, or the FEA may need to be re-run with a refined mesh if the convergence is inadequate). The workflow is the cornerstone of a defensible high-temperature analysis practice.

Steps 1–4: Requirements and operating conditions

1. Step 1 — Requirements: Define the structural requirements — the function, the design life, the safety margin, the applicable design code and the acceptance criteria. Identify the safety-critical aspects and the consequences of failure.
2. Step 2 — Operating temperature: Determine the operating temperature range — the steady-state temperature, the transient temperatures (start-up, shutdown), the spatial distribution (gradients) and the temporal variation. Establish the temperature uncertainty (measurement accuracy, spatial variation).
3. Step 3 — Duration: Define the service duration — the design life, the operating profile (steady-state, cyclic, intermittent) and the hold times at high temperature. Determine whether the duration is in the primary, secondary or tertiary creep regime.
4. Step 4 — Loads: Define the mechanical loads — the sustained loads (pressure, deadweight, centrifugal), the cyclic loads (transients, pressure cycles), the displacement-controlled loads (thermal expansion) and the occasional loads (seismic, wind). Establish the load uncertainty.

Steps 5–7: Material data, thermal analysis and static stress

1. Step 5 — Material data: Assemble the material data — the temperature-dependent properties (modulus, yield, CTE, conductivity) and the creep properties (creep curves, rupture data, constitutive model constants). Verify that the data covers the service temperature and stress range, and that it is for the correct material condition. Document the data sources and the data quality. Fill gaps with a test programme or conservative assumptions.
2. Step 6 — Thermal analysis: Perform the thermal analysis to determine the temperature field — steady-state and transient. Verify the thermal analysis against measurements where available. The temperature field is the input to the structural and creep analysis.
3. Step 7 — Static stress: Perform the static (elastic or elastic-plastic) stress analysis at the operating loads and temperature. Identify the stress concentrations and the critical locations. Determine the initial stress state (including preload, residual stress and thermal stress). This is the starting point for the creep analysis.

Steps 8–10: Creep model, calibration and FEA

1. Step 8 — Creep model selection: Select the creep constitutive model based on the material, the loading history, the duration and the life-limiting mechanism (as described in the model selection article). Document the selection and the justification.
2. Step 9 — Model calibration: Calibrate the creep model constants to the material test data. Verify the calibration by reproducing the test data. Validate the calibrated model against data not used in the calibration. Document the calibration and the validation.
3. Step 10 — FEA: Perform the creep FEA with the selected model, the calibrated constants, the temperature field and the loads. Use appropriate time stepping (verified for convergence) and mesh (verified for convergence). Apply the correct initial stress state (from Step 7). Run the analysis for the full service life (or the relevant portion).

Steps 11–13: Deformation, rupture and creep-fatigue

1. Step 11 — Deformation assessment: Extract the creep strain, total strain and displacement from the FEA. Compare the deformation to the allowable (clearance, ovality, sag, elongation). Identify any locations where the deformation exceeds the allowable.
2. Step 12 — Rupture and life assessment: Assess the creep rupture life at the critical locations (which may differ from the maximum elastic stress location due to redistribution). Use the stress and temperature history from the FEA and the rupture correlation (stress-rupture curve or time-temperature parameter). Compare the predicted life to the design life with the safety factor. Account for the material scatter (use a lower-bound curve for safety-critical assessments).
3. Step 13 — Creep-fatigue assessment (where relevant): If the component experiences cyclic loading at high temperature, assess the creep-fatigue interaction. Compute the fatigue damage (from the cyclic strain range) and the creep damage (from the hold time). Combine the damage using an interaction rule based on test data or an established procedure. Compare the combined damage to the acceptance criterion. Do not invent universal acceptance limits — use the applicable code or a documented basis.

Steps 14–15: Sensitivity, verification and reporting

1. Step 14 — Sensitivity and verification: Perform a sensitivity analysis for the key parameters (temperature, stress, material constants, geometry). Quantify the uncertainty in the predicted life and deformation. Verify the FEA (single-element test, benchmark, convergence study). Validate the analysis against test data and service experience where available. Document the verification and validation.
2. Step 15 — Reporting: Prepare the analysis report documenting the requirements, the operating conditions, the material data (with sources), the thermal analysis, the static stress analysis, the creep model (with selection justification and calibration), the FEA (with mesh, time stepping and convergence), the deformation assessment, the rupture/life assessment, the creep-fatigue assessment (if applicable), the sensitivity analysis, the uncertainty, the verification and validation, and the conclusions. The report should be traceable (every result can be traced to its inputs) and defensible (every assumption and method is justified).

Cross-references and iteration

The workflow is not strictly linear — several steps may require iteration. If the material data (Step 5) is inadequate for the selected model (Step 8), the data must be supplemented or a simpler model selected. If the FEA (Step 10) does not converge (Step 14), the time stepping or the mesh must be refined and the FEA re-run. If the deformation (Step 11) or the life (Step 12) does not meet the requirements (Step 1), the design must be modified and the analysis re-run. The workflow should be applied with engineering judgement — the steps are a framework, not a rigid prescription. The cross-references between the steps and the companion articles in this Knowledge Base provide the detailed guidance for each step. The workflow is the integrating framework that ties the individual topics together into a defensible analysis process.

• High-Temperature Structural Analysis Fundamentals
• Creep Analysis Material Data Requirements
• Finite Element Analysis of Creep
• Creep Rupture Fundamentals
• Creep-Fatigue Damage Assessment
• Sensitivity Analysis in Creep Assessment
• Creep Analysis Verification & Validation
• Verification & Validation — Model Quality
• Failure Analysis & Structural Integrity

A defensible high-temperature analysis is not a single calculation — it is a structured 15-step workflow that covers the full scope from requirements to reporting. Every step must be performed, every assumption must be justified, and every result must be traceable. A shortcut at any step can invalidate the analysis. Follow the workflow, document each step, and the analysis will be defensible.

Configuration control and independent review

The final workflow should be configuration-controlled so that the reported conclusion can be reproduced. Geometry revision, mesh, material dataset, thermal field, load history, constitutive constants, solver version, scripts and post-processing definitions should be identifiable from the analysis record. This is particularly important in long-duration assessments, where small changes to material data or operating history can materially alter life. For safety- or mission-critical work, an independent technical review should challenge the governing assumptions, critical locations, extrapolations, sensitivity cases and acceptance logic rather than merely checking arithmetic. The review should confirm that the analysis answers the engineering requirement originally defined in Step 1 and that no later modelling refinement has quietly changed the assessment basis. Configuration control and independent review turn a technically good calculation into evidence that can be relied upon later.