PRELIMINARY PIPE STRESS ANALYSIS OF HIGH PRESSURE, HIGH TEMPERATURE EXPERIMENTAL HELIUM COOLING SYSTEM

A.K. VERMA, B.K. YADAV, A. GANDHI, A. SARASWAT, S. VERMA, E.R. KUMAR PRELIMINARY PIPE STRESS ANALYSIS OF HIGH PRESSURE, HIGH TEMPERATURE EXPERIMENTAL HELIUM COOLING SYSTEM A.K.VERMA Institute for Plasma Research Bhat, Gandhinagar, Gujarat, India Email: adityakumar@ipr.res.in B.K. YADAV, A. GANDHI, A. SARASWAT, S. VERMA, E. R. KUMAR Institute for Plasma Research Bhat, Gandhinagar, Gujarat, India Abstract Institute for Plasma Research (IPR) is developing an Experimental Helium Cooling Loop (EHCL) as a part of R&D activities in fusion blanket technologies. EHCL is similar to the First Wall Helium Cooling System (FWHCS) of LLCB TBM and in this loop first wall mock ups up to one fourth size of blanket can be tested. The Test Section Module (TSM) of EHCL is designed to remove heat load of ~75 kw. Similar to the FWHCS, EHCL is also high-pressure high-temperature system which produces significant moments in the piping system. This leads to forces and moments in the piping support and equipment nozzles. During the earthquake, a high acceleration acts on the piping system due to this the deflection of pipes may increase the difficulty of loop operation. The paper describes the optimized loop layout of EHCL, methodology and results of pipe stress analysis. EHCL process layout is designed in a limited space (64 m 2 ). All major equipment are installed and connected through the piping and associated valves. For the protection from high energy pipes and other safety reasons, entire process area is protected by strong barricade. The pipe stress analysis is performed for sustained and occasional (earthquake) load combinations of various operating cases envisaged for TSM mock ups. The process piping code ASME B31.3 is referred for pipe stress analysis. The calculated stresses are in acceptable limit. The least available value of stress margin (about 0.29 times the allowable stress) and the corresponding displacement of 9.8 mm (x direction), 19.72 mm (y direction) and 21.76 mm (z direction) is observed in heater to TSM line. The obtained reaction and moment force results are needed as an input for the selection of pipe supports and location of supports. This pipe stress analysis results are used in the optimization of EHCL layout and further these inputs would be utilized in final design phase. 1. INTRODUCTION Experimental Helium Cooling Loop (EHCL) is a high-pressure high-temperature closed loop helium gas system [1]. This helium loop is similar to the FWHCS and designed mainly for testing various component mock-ups, which are cooled by high temperature and high pressure helium [2], [3]. The Test Section Module (TSM) mockups will undergo a series of mock-ups qualification tests for design and performance validations. The design of EHCL shall also allow experiments with any other high heat flux helium-cooled components that can be operated within the loop operating range. Major objectives of EHCL are to study the dynamics of the system at different operating conditions (shown in Table 1) and to understand the loop operation & control with associated safety aspects. To take care of pressure fluctuations & loss of inventory, the process loop is also equipped with Pressure and Inventory Control System (PICS). The integrated operation of process loop with PICS, and the understanding of high pressure high temperature piping behavior are essential for final development of EHCL. The paper mainly presents EHCL optimized loop layout and results of pipe stress analysis. 2. SYSTEM DESCRIPTION EHCL is designed for 10 MPa pressure, 450 C temperature and 0.4 kg/s flow rate. The selected size for the connection pipes is DN 50 schedule 80. The maximum operating pressure and temperature are 8 MPa and 400 C respectively [1]. The details of process parameters of EHCL are shown in Table 1. Table 1. Details of process parameters of EHCL Parameters Operating Design Heat load for TSM, kw 18-75 75 Temperature at TSM, C 100-400 450 Coolant pressure (Helium), MPa 8.0 10.0 Coolant flow rate (Helium), kg/s 0.4, 0.3, 0.2, 0.1 0.4 1

IAEA-CN-123/45 EHCL loop consists of circulators, heater, recuperator, coolers, compressors, vacuum pumps, control and safety valves, associated piping, and necessary instrumentation and control systems (shown in Fig. 1 & 4). FIG. 1. Process flow diagram of EHCL The P&ID of EHCL is presented in Fig. 1.The loop consists of a hot leg and cold leg, which are connected by recuperator. In the hot leg, TSM and electrical heater are placed, while in the cold leg circulators, dust filters and coolers are placed. In the TSM outlet line, the hot helium temperature is first reduced by the recuperator and then by the cooler. This scheme enables cold leg operation in a temperature range of 50-200 C and allows the components in the cold leg to operate in a lower temperature environment which simplifies the design of the components. In the cold leg between the recuperator and cooler, helium temperature range is 100-200 C, while between cooler and circulator discharge line, the temperature range is 50-100 C. The hot leg is designed to accommodate maximum operating temperature of 400 C and in this portion of loop helium operating temperature range is 300-400 C. Maintaining low temperature helium to the suction of the helium circulator reduces circulator power requirement. In the loop, two parallel circulators, each of 0.2 kg/s mass flow rate capacity are assembled. Based on the flow rate requirements, one or both the circulators shall be operated. Before the circulators, dust filters are installed to filter the metallic dust of the system. 3. MODELLING AND METHODOLOGY EHCL plant layout is prepared with the help of CATIA V5 modelling tool [4]. 3D layout of EHCL consists of equipment arrangement, pipe routing, supports, cable tray routing, instrumentation arrangement and impulse tube routing. The EHCL lab is constructed in 324 m 2 area, which consists of process loop, control & monitoring room, panel room, storage and maintenance area. The entire process area is fenced with metallic barricade (shown in Fig. 2).

A.K. VERMA, B.K. YADAV, A. GANDHI, A. SARASWAT, S. VERMA, E.R. KUMAR FIG. 2. EHCL internal arrangement (Process area with protective grid) High temperature pipes are routed from the top part of the facility. The necessary flexible supports and pipe looping are also foreseen in the loop layout. The high temperature lines of EHCL are insulated with CERAWOOL [5]. Insulation covers 20% more volume of the process area, but as estimated, sufficient space is still available for maintenance activities within the process area. For the routine inspection, 0.5 m space margin is available surrounding to all major components. FIG. 3. Access for inspection in EHCL process area The Reliability, Availability, Maintainability and Inspectability (RAMI) aspects are also taken into account during EHCL layout preparation. The inspection and maintenance access is shown in Fig. 3. The optimized layout is simplified for the piping analysis as shown in Fig. 4.The coordinates of EHCL pipes are used to recreate pipe models in CAESAR II software. The data exchange tools are not utilized in order to avoid common problems such as loss of bodies from the assemblies, displacement of original positions, and modification in the graphic information [6]. 3

IAEA-CN-123/45 FIG. 4. Simplified EHCL model for piping analysis CAESAR II version 5.30 is used as an analysis tool and ASME B31.3 as a reference code chosen for the analysis of EHCL pipes [7]. The modelled EHCL pipes in CAESAR II software are shown in Fig.5. FIG. 5. Modelling of EHCL pipes in CAESAR II for piping analysis

A.K. VERMA, B.K. YADAV, A. GANDHI, A. SARASWAT, S. VERMA, E.R. KUMAR The pipe stress analysis is performed for maximum operating conditions of EHCL (refer Table 1). The analysis is performed for sustained and occasional load cases. The sustain loads are due to the pressure, temperature & dead weight while the occasional loads are the additional seismic loads (earthquake loads) on the sustained loads. The input parameters considered for the analysis are illustrated in the Table 2. Table 2. Details of input data for CAESAR II analysis CAESAR Parameters Input values Design Code ASME B31.3 Pipe material SS 316 L Pipe size DN 50 schedule 80 Hot leg Temperature values, C 25,300,350,400 Cold leg Temperature values, C 25, 80, 100 Coolant pressure values, MPa 6.0,8.0,8.5, 10.0 Pipe density, kg /m 3 7850 Fluid density, kg /m 3 12.86 CERAWOOL density, kg /m 3 128 Mill tolerance % 12.5 Thermal Cycles 60,000 Allowable Stress at room temperature, MPa 115 Thermal insulation thickness for hot leg pipes, mm 100 The insulation thickness is calculated for minimum heat loss, maximum efficiency and personnel protection. The insulation thickness is estimated from 3EPlus software [8].The EHCL pipes are designed in compliance with ASME B31.3 code considering various loading conditions (operational state, maintenance and standby) [9]. The load combinations for the analysis of EHCL pipes are shown in Table 3. Table 3. Load combinations of EHCL pipes Load combination Loads Max. events Normal operation (Sustained Load Case) DW+P+T 60,000 Normal operation+ SL (Occasional Load Case) DW+P+T+ Occasional 1 IPR lies in seismic zone III and the process loop is planned to be located at ground floor of EHCL lab at IPR. FRS of Gandhinagar was used to find out the induced stress in the process loop during seismic event. The considered operational states, process parameters and load combinations for the pipe stress analysis are presented in the Table 4. Table 4. Load combinations of process piping as per planned operational states Mock-ups operational States Operational States Process parameters Load Combinations Sustain Loads Occasional Case Operation State (POS) Normal Operation State P= 7.8-8.3 MPa, T=300-400 C, F = 0.2-0.4 kg/s L1= DW+P1 (Sustain Case) L2= DW+P2 (Sustain Case) L3= DW+T1+P1 (Operating Case) L4= DW+T2+P2 (Operating Case) L5= L3-L1 (Expansion Case) L6= L4-L2 (Expansion Case) L1+ Occasional L2+ Occasional L3+ Occasional L4+ Occasional L5+ Occasional L6+ Occasional Short Term Standby (STS) Cold Standby State RP = 4.0-6.0 MPa T = 280-300 C, L1= DW+P1 (Sustain Case) L2= DW+T1+P1 (Operating Case) L1+ Occasional L2+ Occasional 5

IAEA-CN-123/45 RF = 0.2 kg/s, Ramping Baking state RP = 1.0 MPa, Temp. = 25-300 C, RF ~ 10% of F L3= DW+T2+P1 (Operating Case) L4= L2-L1 (Expansion Case) L5= L3-L1 (Expansion Case) L1= DW+P1 (Sustain Case) L2= DW+T1+P1 (Operating Case) L3= L2-L1 (Expansion Case) L3+ Occasional L4+ Occasional L5+ Occasional L1+ Occasional L2+ Occasional L3+ Occasional Long Term Maintenance (LTM) Maintenance state Ambient conditions L1= DW+P1 (Sustain Case) L1+ Occasional DW= Dead weight, P = Pressure, T = Temperature, F = Flow, RP = Reduced Pressure, RF = Reduced Flow. 4. RESULTS The major equipment of EHCL are connected with DN 50 schedule 80 pipes. The pipe material SS316 L is used for connection pipes. The temperature dependent properties of SS316 L are considered for the analysis. The summary of pipe stresses and displacements results during normal operation conditions are shown in Fig. 6. FIG. 6. Pipe stresses and displacements during normal operation condition The summary results of EHCL pipes for sustained, thermal and occasional load cases are presented in Table 5. The stress margin is calculated as margin = (1 - Stress ratio) 100. Whereas; Stress ratio = Calculated Stress / Allowable Stress. Table 5. Summary of results for pipe stresses, displacements and reaction forces Load Cases Available Stress margin % Calculated Stress % Dx, mm Displacements Dy, mm Dz, mm Fx, N Reaction Forces Fy, N Fz, N

A.K. VERMA, B.K. YADAV, A. GANDHI, A. SARASWAT, S. VERMA, E.R. KUMAR Sustained Load (W+P) 68.5 (1560) 31.5 (1560) -1.28 (1470) -0.89 (2460) -9.34 (2460) 598 (1200) -318 (630) -792 (520) Thermal Load (T) 43.1 (1100) 56.9 (1100) -8.43 (1680) 15.20 (1470) 17.26 (2460) -1437 (1380) -1931 (630) -6237 (970) Occasional Load (W+P+ Occasional) 29.4 (1470) 70.6 (1470) 9.80 (2394) 19.72 (2390) 21.76 (2390) 1638 (1200) 1044 (2020) 1024 (520) The highest value of stress about 0.706 times of allowable stress limit is estimated for Electric heater to TSM line. The maximum displacement of 9.8 mm (x direction), 19.72 mm (y direction) and 21.76 mm (z direction) is also observed in the same line. The pipe displacements would be considered during the installation of mechanical supports. The obtained reaction force results would be utilized as an input for the pipe support design. The natural frequency of the integrated EHCL piping system is 4.1 Hz. The dominating natural frequencies in X, Y & Z directions are mentioned in the Table 6. Table 6. Dominating natural frequencies and mass participation factor in X, Y & Z directions Directions Natural Frequency, Hz Mass Participation factor X 6.3 0.04515 Y 4.1 0.17246 Z 5.4 0.03385 The parameters used for the EHCL pipe stress analysis are the maximum allowable temperature and pressure. EHCL piping qualifies to meet the code stress criteria as per the process piping code paragraphs 302.3.5 for sustained loads, 302.3.6 for occasional loads and 319.4.4 for thermal expansion loads for all static and dynamic load conditions. 5. CONCLUSIONS The 3D loop layout of EHCL is modelled in CATIA V5 software. The layout also addresses clash and RAMI aspects. The piping network is used for pipe stress analysis using CAESAR II version 5.30 in accordance with process piping code ASME B31.3. In contemplation of high temperature facility, this loop is also associated with flexible looping patterns (e.g. C and S type) to avoid excess stresses in the piping network. Further, the pipe stresses are checked for sustained loads, thermal expansion loads and occasional loads at maximum operating conditions of process loop. The calculated stresses are below the allowable values for all the cases mentioned in Table 4 and sufficient margins are available in the pipes. The accepted code stress criteria verifies the integrity of piping system. The present design is to be further analyzed for whip load, fire load and other assembly loads. This analysis may lead to slight change the loop layout and accordingly the stresses would be reassessed. REFERENCES [1] B. K. Yadav, A. Gandhi, A. K. Verma, et al., Conceptual design of experimental helium cooling loop for Indian TBM R&D experiments, world academy of science, engineering and technology Int. J. Physical and Mathematical Sciences, 8 (2) (2014). [2] B.K. Yadav, A. Gandhi, A.K. Verma, et al., Helium Cooling Systems for Indian LLCB TBM, Fusion Engineering and Design, 124 (2017) 710 718. [3] A.K. Verma, B.K. Yadav, A. Gandhi, E.R. Kumar, et al., Pipe stress analysis of first wall helium cooling system for conceptual design development of IN LLCB TBM, Volume 137, December 2018, Pages 130-136. [4] 3D Modeling Solutions CATIA - Dassault Systèmes 7

IAEA-CN-123/45 [5] Ceramic fibre blankets - Morgan Thermal Ceramics (http://www.morganthermalceramics.com/media/2595/rcfblankets_murugappa.pdf) [6] Lubomir DIMITROV, Fani Valchkova, Problems With 3d Data Exchange Between Cad Systems Using Neutral Formats, Proceedings in Manufacturing Systems, Volume 6, Issue 3, 2011 ISSN 2067-9238. [7] CAESAR II - Pipe Stress Analysis coade [8] Pipe Insulation Calculate Thickness 3E Plus Software [9] Process Piping Code ASME B31.3