Simulations for Structural Integrity Assessment at TWI

What is Structural Integrity? Why is it important?

New and aging assets may not live up to their intended design life. For that reason, structural integrity assessment is an engineering field that plays a fundamental role in ensuring that structures are fit to do what they are designed to under normal operating conditions and are safe when conditions exceed the original design intent. Integrity is not just a case of good design; it needs to be maintained and periodically assessed throughout the life of a structure.

The most common damage mechanisms to structural integrity are:

Corrosion (local metal loss)
Fatigue (due to cyclic loading)
Crack-like flaws (due to fatigue or welding defects)
Creep damage (high-temperature applications)

Established fitness-for-service (FFS) and engineering critical assessment (ECA) standards such as API 579/ASME FFS-1 and BS 7910 provide the approaches and calculation methods to assess the susceptibility and acceptability of the above damages on simple structural configurations. However, when structure configurations and loadings are more complex, the damage is near a structural discontinuity, or there is a desire to reduce the conservatism in the assessment, Finite Element Analysis (FEA) can be used to provide a more accurate result.

Finite Element Analysis at TWI

TWI’s modeling team are world-leading experts in applications of FEA for structural integrity assessments. The Numerical Modelling and Optimisation section at TWI is made-up of Chartered Engineers, Chartered Mathematicians, and NAFEMS-certified Professional Simulation Engineers. TWI offers a variety of computational engineering capabilities including FEA, computational fluid dynamics (CFD), and data analysis. Our team sits as members of the British Standard 7910 committee, the UK nuclear structural integrity code R6, and are highly cited researchers in fracture, fatigue, and damage mechanics, having recently received an award from the International Conference on Ocean, Offshore and Artic Engineering (OMAE).

Figure 1: Level 3 FFS for metal loss on an aboveground storage tank

Assessing Structural Integrity with FEA

TWI identifies and applies the most appropriate technology to support our client's decisions regarding the safe operation of a structure. Our activities span across the aerospace, automotive, oil & gas, and power generation sectors, and include the structural integrity assessments for:

FEA for an FFS on crack-like flaws on a power boiler reheater header
Creep analysis using FEA for an FFS on the main steam pipeline found susceptible to creep damage
Creep-relaxed stress analysis using FEA for an FFS on high-energy piping of a power boiler
Fracture and fatigue of petroleum road fuel tankers with the results presented to UK Parliament
Corrosion of well conductors, incorporating in-line inspection (ILI) data directly in the models
Dents and gouges of subsea pipelines that were identified by Remotely Operated Vehicles
Tubular joints in offshore jacket structures, using constraint-based fracture mechanics
Fracture and strength of radioactive waste disposal canisters
Hydrogen-induced stress cracking (HISC) of duplex stainless steel joints for subsea service

TWI has internationally-recognized laboratories for materials characterisation, fracture and fatigue testing, environmental testing, and full-scale performance qualification. The modeling techniques that TWI applies for structural integrity assessments have been validated experimentally with decades of evidence to give confidence to our clients.

For more infomation please email:

engineering@twisea.com