preliminary pipe stress analysis of high pressure, … · this pipe stress analysis results are...

A.K. VERMA, B.K. YADAV, A. GANDHI, A. SARASWAT, S. VERMA, E.R. KUMAR

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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: [email protected]

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 m2). 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) mock-

ups 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

mailto:[email protected]

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 m2 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).


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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].

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


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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 /m3 7850

Fluid density, kg /m3 12.86

CERAWOOL density, kg /m3 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)


L3= DW+T1+P1 (Operating Case)


L5= L3-L1 (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+ Occasional

L2+ Occasional

IAEA-CN-123/45

RF = 0.2 kg/s,




L3+ Occasional

L4+ Occasional

L5+ Occasional

Ramping Baking state RP = 1.0 MPa,

Temp. = 25-300 °C,

RF ~ 10% of F




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 %

(Node)

Calculated

Stress

%

(Node)

Displacements Reaction Forces

Dx, mm

(Node)

Dy, mm

(Node)

Dz, mm

(Node)

Fx, N

(Node)

Fy, N

(Node)

Fz, N

(Node)


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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

http://waet.org/author/b-k-yadav

http://waet.org/author/a-gandhi

http://waet.org/author/a-k-verma

IAEA-CN-123/45

[5] Ceramic fibre blankets - Morgan Thermal Ceramics (http://www.morganthermalceramics.com/media/2595/rcf-

blankets_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

https://insulationinstitute.org/tools-resources/free-3e-plus/

preliminary pipe stress analysis of high pressure, … · this pipe stress analysis results are...

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