RemLife™

Across industries, determining the structural integrity and remaining life of assets plays a key role in effective asset management. With ALS’s RemLife software, our clients have unparalleled confidence knowing their asset’s risk profile is minimal and life-cycle profitability is maximised.

The ALS RemLife software provides asset managers with optimisation solutions for their asset’s productivity and life-cycle profitability. Within this, the assessment of creep, creep-fatigue and fatigue damage and associated costs can be estimated for different operating scenarios.

RemLife software is utilised by asset managers and engineers to perform rapid, cost effective and accurate Fitness-For-Service and remaining life assessments on plant operating at elevated temperatures or pressures, or both. These assessments provide an understanding of the asset condition and damage accumulated due to base load operation or cycling due to pressure, temperature transient conditions.

The ALS RemLife remaining life assessment approach delivers outcomes superior to a Level 2 EPRI defined life assessment for creep rupture, creep-fatigue and low cycle fatigue analysis where the stresses are determined via the software using integral analytical stress solutions and a full Level 3 assessment where Finite Element Analysis (FEA) determined stresses can be directly entered.

Remaining life assessment and cycling of plant within the power industry

Due to changes in demand and competition, many power plants such as coal fired, combined cycle gas and thermal solar plants are subject to flexible operation. A feature of flexible operation is that units may cycle in a 2-shift pattern and also if running at close to design output, are expected to respond rapidly to load changes on the system, thus ensuring that the grid maintains the specified frequency and voltage.

Due to the rigorous demands imposed by load varying operations in competitive markets, asset managers need to quantify the incremental costs of cycling generating units to ensure profitability and to better select, run, and upgrade production units. Furthermore, technical, operations, and maintenance staff need to understand, plan, and react to the complex nature and interaction of equipment, processes, and failure modes brought on by cycling.

RemLife software was originally developed by Australian Nuclear Science and Technology Organisation (ANSTO) Dr. Warwick Payten, one of Australia’s leading experts in the field of high temperature remaining life assessment and fracture mechanics, specifically for the power industry. With the ability to break down complex plants into simple components, RemLife can be utilised effectively in various other process industries where creep, low cycle fatigue and creep-fatigue may occur. This can include components such as refinery heaters, reactors, reformers and coker’s.

RemLife™ Software

The software was originally designed to bridge the gap between ‘back of the envelope’ calculations for base rupture and fully detailed finite element analysis for creep-rupture and combined creep-fatigue analysis. It enables a quick and easy screening approach and understanding to which assets are at risk due to their past and planned future operating regime, as well as a detailed approach for components which are determined to be at risk. Future operational regimes can be rapidly assessed and their impact on the component calculated.

Since its beginnings in 2005, RemLife has been developed into a full Fitness-For- Service software package with several highly integrated submodules that allow a seamless transition from a crack initiation to crack growth studies. Beyond this, RemLife assessments can study the remaining life of boiler and superheater tubes based on oxide thickness readings, and assessment the localised thinned areas at room and elevated temperatures in the creep range.

(*) Finite Element Analysis (FEA) stress results can be entered directly for a Level 3 assessment.

The creep-fatigue crack initiation module of the RemLife software uses a combination of methodologies to calculate both the base rupture damage as well as the cyclic damage due to start-ups and shutdowns. This is achieved under the guidelines of the EDF Energy R5 “Assessment Procedure For The High Temperature Response of Structures”, based on time fraction, ductility exhaustion, and strain energy density exhaustion.

CrackLife, the fracture mechanics and module integral to the RemLife software, is based on the guidelines of BS7910 “Guide to methods for assessing the acceptability of flaws in metallic structures” and the EDF R6 code for the assessment of the integrity of structures containing defects. For high temperature the R5 code which deals with the more complex issues of combined loading at high temperatures.

The TubeLife module is based on internationally recognized research results for oxide kinetics for steal in a steam touched environment. It allows the calculation of remaining life of boiler and superheater tubes based on oxide thickness field measurements.

ScarLife module is based on BS7910 contained procedure an augments for the assessment of localised thinned areas at ambient and elevated temperatures within the creep range. 

A number of international design standards are used for the calculations of primary and secondary stresses. These are based on the use of analytical expressions for the determination of thermal stress, using an analytical expression for metastable thermal stresses and mapped thermal stress response.

Cycle Costing Module is a simulator based on general economic solutions that allows the effects of unit cycling on both the damage sustained by the equipment and the economic benefits or not of the chosen cycling regime to be studied.

The principal factors to be considered during cyclic operation are:

• Increased capital spend for component replacement.
• Increased routine 0&M cost from higher wear and tear.
• Lower availability due to increase in failure rate and increased outage time.
• Increased fuel cost from reduced efficiency and non-optimum heat rate.

This gives the ability to rapidly run different load profiles and shifting strategies to gauge the impact on individual components and the unit as a whole.

Creep-Fatigue and Fatigue Initiation Calculations

Utilises the methodologies supported by following approaches:

R5 & R6, API579/ASME FFS-1 and RCC-MR:

• Time fraction approach
• Ductility exhaustion
• Strain energy density exhaustion

Creep, Creep-Fatigue and Fatigue Crack Growth

BS7910, R5 & R6, API579/ASME FFS-1:

• Extensive library of stress intensity and reference stress solutions
• C*
• C(t)
• Paris Law

Extensive Material Library

Stress calculations can be performed utilising the following codes or via finite element analysis:

RemLife™ Calculations

The following calculations are typically performed as part of the assessment:

Initiation Study:

• Determine the loading history.
• Calculate metastable thermal stresses.
• Determine the cyclic stress-strain deformation loops.
• Obtain creep-fatigue endurances.
• Calculate the total creep-fatigue damage.
• Assess whether crack initiation will occur.
• Calculate economic consequences of cyclic damage.

Crack Growth Study:

• Calculate the crack growth rates for creep, creep-fatigue or fatigue.
• Incorporate findings into the Failure Assessment Diagram (FAD) for mode of failure and life prediction.
• Determine the critical defect size.