Elevated-Temperature Life Assessment

This article provides some new developments in elevated-temperature and life assessments. It is aimed at providing an overview of the damage mechanisms of concern, with a focus on creep, and the methodologies for design and in-service assessment of components operating at elevated temperatures. The article describes the stages of the creep curve, discusses processes involved in the extrapolation of creep data, and summarizes notable creep constitutive models and continuum damage mechanics models. It demonstrates the effects of stress relaxation and redistribution on the remaining life and discusses the Monkman-Grant relationship and multiaxiality. The article further provides information on high-temperature metallurgical changes and high-temperature hydrogen attack and the steps involved in the remaining-life prediction of high-temperature components. It presents case studies on heater tube creep testing and remaining-life assessment, and pressure vessel time-dependent stress analysis showing the effect of stress relaxation at hot spots.

Corrosion and Remaining Life Assessment

This article illustrates the use of the fitness-for-service (FFS) code to assess the serviceability and remaining life of a corroded flare knockout drum from an oil refinery, two fractionator columns affected by corrosion under insulation in an organic sulfur environment, and an equalization tank with localized corrosion in the shell courses in a chemicals facility. In the first two cases, remaining life is assessed by determining the minimum thickness required to operate the corroded equipment. The first is based on a Level 2 FFS assessment, while the second involves a Level 3 assessment. The last case involves several FFS assessments to evaluate localized corrosion in which remaining life was assessed by determining the minimum required thickness using the concept of remaining strength factor for groove-like damage and evaluating crack-like flaws using the failure assessment diagram. Need for caution in predicting remaining life due to corrosion is also covered.

Comparative Study on Remaining Life Assessment of a Pressure Vessel, Working in Severe Conditions, Based on Results of Metallographic Replicas and Creep Tests

The paper presents and compares the results on the reliability and remaining life assessment of a reactor (coxing box) from a petrochemical plant. The reactor shell is made of 16Mo5 (W1.5423) steel, with a thickness of 25 mm, plated with 3 mm thick X6CrAl13 (W1.4002) stainless steel. The assessment was made in two steps. For preliminary remnant life assessment, specifications of section VII of the ASME code was used followed by iRiS‑Thermo expert system. Further, experimental creep and metallographic replica analysis were performed. Results comparison of the two methods applied revealed a reduction of the preliminary estimated remaining live obtained using metallographic replica analysis. Based on the results obtained, the possibility to extend the service duration of the coxing box in the safety condition, using current process parameters, with of 20.000 hours was highlighted.

REMAINING LIFE ASSESSMENT DAN KASUS LAJU KOROSI PADA LPG STORAGE TANK KAPASITAS 50 TON

LPG Storage Tank berkapasitas 50 Ton yang telah terinstalasi dan beroperasi sejak tahun 2010 akan dikaji kelayakan dan sisa umur pakai dari pressure vessel tersebut. Metode pengujian yang dipergunakan adalah Non-Destructive Testing (NDT) - Ultrasonic Testing (UT) pada bagian shell dan head untuk mendapatkan nilai actual thickness dari pressure vessel serta dilakukan Visual Examination. Nilai thickness tersebut dipergunakan untuk menganalisis dan mengkalkulasi thickness required (Treq), nilai Corrosion Rate (CR), Maximum Allowable Working Pressure (MAWP) serta umur sisa (Remaining Life) dari LPG Storage Tank tersebut. Dari hasil analisa serta perhitungan maka didapat umur sisa pakai dari LPG Storage Tank kapasitas 50 Ton adalah 18 tahun dengan nilai laju korosi sebesar 0,043 mm/thn

Crude Furnace Floor Creep Assessment and Remaining Life Assessment due to Hot Spots

Fitness for Service (FFS) assessment and remaining life assessment of the furnace floor plates in a crude charge heater where hot spots up to 500°C have been observed during operation in 2018 was undertaken as a pre assessment prior to the unit turnaround. The remaining life assessment results would provide the turnaround team with firm scope for repair in order to resintate the bottom plate and avoid discovery scope. Two Finite Element (FE) models were created to account for hotspot temperature conditions measured at November 2018 and June 2019. Each of these FE models involved successive loading conditions, so that the effects of each loading scenario could be investigated. The loading conditions were applied in steps, in the following order: 1. Gravity. 2. Temperature, modelling hotspot behaviour. 3. Creep, viscoelastic analysis. Utilising the FE models created for the two hotspot conditions, remaining life was calculated and suggested that the worst location for creep damage is near burner 2 (the maximum creep damage location of the November 2018 condition). Based on the assessment, the following recommendations are made: 1. Continue to observe and maintain temperatures below the creep temperature range (i.e. no additional hotspots are created and temperatures are not increasing). 2. Undertake creep testing from metal samples. 3. Re-inspect in 8 years at the same locations where metallographic replication was performed in September 2019.