DESIGN AND ANALYSIS OF TIE-IN CONNECTION SYSTEM

COMPONENTS FOR SUBSEA LABORATORY Keval K. Patil1, D. P. Hujare2, A. H. Purohit3

1Post graduate Student in Dept. of Mechanical Engg. at Maharashtra Institute of Technology, Pune, India 2Associate Professor in Dept. of Mechanical Engg. at Maharashtra Institute of technology, Pune, India

3Principal Engineer- FEA at Aker Powergas Subsea Solutions Pvt. Ltd. Pune, India

kevalpatil@gmail.com

ABSTRACT:

Subsea engineering is a vast field for the design, analysis, construction, installation and integrity management of subsea trees, tie-in connection, manifolds, jumpers, wells. The subsea technology used for offshore oil and gas production is a highly specialized field of application that places particular demands on engineering which carries some unique aspects related to the inaccessibility of the installation, operation and servicing. Tie-in connection systems are used to connect various subsea production system components like tree to tree, pipeline end to tree or manifold, tree to manifold. This article demonstrates design and analysis of scale down parts of tie-in connection system. The FEA results indicate analyzed parts are safe under required standards which further validated by numerical calculations and testing.

Keywords— FEA; LE; MAWP; ROV; CAD

I. INTRODUCTION

Subsea production system is consisting of various components like Manifold, X-mas trees, tie-in connections, oil and gas well. Scale down

models of this parts are designed for subsea laboratory which is under construction. In this study emphasis is given on design and analysis of tie-

in connection system. Tie-in connection systems are the joints between various subsea components and those joints should be automatic and leak

proof. Various types of vertical and horizontal tie-in connection systems and related connection tools are used for the tie-in of flowlines, umbilicals,

and other applications. In the flowlines tie-in systems are used to connect tree to tree, pipeline end to tree or manifold, tree to manifold and for

subsea control systems tie-in systems are used to connect umbilicals to tree or manifold [1].

A. Subsea laboratory

Figure 1 shows the block diagram of subsea laboratory. Production and injection X-mas trees are connected to the manifold using tie-in

connection system. This tie-in connection system is made up of various parts like termination, porch, support frame, guide posts and clamp

connector etc. Porch consist of inboard hub, porch plate and it is fixed parts of Tie-in connection system which is bolted to either X-mas tree or

manifold. X-mas trees and manifold are placed first to their respective positions and then termination with pipeline is placed in between them.

Termination is floating parts which is guided by guide post during and its consist of outboard hub, termination plate and clamp connector. Support

frames are attached to the guide posts which supports the termination during the installation [2].

Figure 1 Block diagram of subsea laboratory

Hub is nothing but the end of the pipe line. End of the pipeline which is connected to the x-mas tree is inboard hub and which is connected to

termination is called outboard hub. The clamp connector is used to join these two ends. The clamp connector is closed by rotating some stud bolts.

The stud bolts are rotated by remotely operated vehicle (ROV). Between the hubs, O-rings and a metal-to-metal seal gives sealed connection. Subsea

pipeline connections nowadays are connected by use of a connection tool called asstroke tool and torque tool operated by a ROV. The ROV arms

activate hydraulic valves on the tool then ROV provides the tool with hydraulic power and the whole connection operation can be observed using

cameras placed on the ROV [3].

The above study highlighted the invention in the techniques used for the connecting various subsea components and it also describes the process

related to tie-in connection components design and installation. However, the final connection of tie-in is often a forgotten theme and seems almost

like an industry secret. This article contains design and verification of various components of tie- in connections system of subsea laboratory.

II. NEED AND OBJECTIVE

Modern subsea fields are moving deeper and deeper from the seashore and use of drivers for manual connection of tie-in connection system is

defunct. Fully automatic tie-in connection using clamp connector is necessary as subsea fields are now more than 1000m deeper and humans can

reach up to 400m deep from sea surface. Standard designs of tie-in connections are set for the 6-inch pipe line connections and as a scale down

model this subsea laboratory has 2-inch pipe line. The key challenge for this study is to design and analyses of tie-in components for 2-inch pipe line

to satisfy installation, operation and testing conditions.

III. ANALYTICAL CALCULATIONS A. Clamp Connector Analysis

a. Axial force acting on the clamp [4]

������ � ��� ∗ 2π cos θ2 sin� � �µ �1�

Figure 2 Equilibrium of bolt forces and radial clamp line loads.

b. The tangential bending stresses

���� � ��� ∗ ���–�� �!" ∗ C$ % δ&'()*I&'()* �2�

Nomenclature

θ = Hubs slop

µ = coefficient of friction between hub and clamp

P = Pressure inside the hub

MI = Moment at the hub centre due to bolt load

RHO = Outside radius of hub neck

RHi = Inside radius of hub neck

R = Inside radius of hub

Ic = Height of the lip

Fblolt= Bolt load on the clamp

Faxial = Axial force acting on the clamp

S = First moment of inertia w.r.t. base line

Ibase = Moment of inertia of the clamp w r t base

Iclamp= Moment of inertia w r to principle axis

R = Inside radius of hub

M = Moment in N.m

σ = Stress induced in the component in N/mm2

r = distance between the force and circular pipe

Cw= Width of the clamp

Ct = Thickness of the clamp

tip = Thickness of the lip at the tip

tbase = Thickness of the lip at the base

Aclamp= Cross sectional area of the clamp

Ar= Cross sectional area of the clamp body without lip

Ic = Height of the lip

Mlip= Moment at the lip of clamp segment

F= Bolt pretension load in N

c. Longitudinal stress at outer surface of the clamp [4]

���� � F(-.('A&'()* � 6 ∗M'.*C$2 �3�

B. Hub analysis

a. Bolt Pretension (F) calculation,

b.

4 � �2 56� �µ ∗ 78cos 9 � 7: ∗ µ; �4�

c. Longitudinal stress developed in the hub because of bold load

d.

�= � % π ∗ P ∗ R@.2 �M'πAR@B2 %R@.2 C �5�

c. Axial stress developed inside the hub [4]

�2 � E ×G2 × 5 × GH2 � 2 × GH × G �G2AGHI � 2 ×GHJ × GC– A2 × GH ×GJC % G �6�

e. Longitudinal stress developed in the hub because of stroke tool load

f. �J � M ∗ KL �7�

e. Von-mises stress calculation

�NOP � QA�=2 %�22C ∗ A�22 %�J2C ∗ A�=2 %�J2C2 �8�

C. Support frame analysis

a. Tensile stress acting on the body, � � 4 ∗ KL �9�

b. Torque acting on pipe end due the force F T � F ∗ r �10�

c. Shear stress acting on the body,

W � XY �11� d. Max principle stress acting on pipe

�Z�� � �2 � Q5[�2\2 � AW2C; �12� e. Min principle stress acting on pipe

�Z�� � �2 % Q5[�2\2 � AW2C; �13�

f. Von-mises stress developed

�N] � ^�A�=2C–�= ∗ �2 �A�22C� �14�

IV. METHODOLOGY A. Cad modelling

In the present study of tie- in connection system, scale down models of various parts of tie-in connection system are modelled according to design

requirements. CAD software Solid works is used to create geometry.

Figure 3 Tie-In connection system

Figure 4 FE model of hub assembly

B. Finite element analysis

Commercial CAE software Abaqus 6.13-4 is used to carry out the analysis. The installation strength analysis performed on the hub assembly,

termination plate and support frame. The objective of the analysis is to investigate that the design is able to handle the design and testing loading

conditions. C3D8R: An 8-node brick with reduced integration and hourglass control type elements are used for meshing. The mesh refinements

are considered at more utilization parts of assembly. Materials and material properties used for assemblies are shown in the table below.

SS316L is the standard molybdenum-bearing grade which is the low carbon version of 316 grade stainless steel. It has excellent corrosion resistance

capability with excellent weldability. Best choice for marine application that’s why called as marine-grade steel. Nickel alloy 625 is excellent

corrosion resistance and high strength nickel based alloy [4]. The finite element models of Assemblies are simplified for the analysis which can

be seen in Figure 4, Figure 5 and Figure 6.

TABLE I

MATERIAL PROPERTIES

MATERIAL ELASTIC MODULUS

[GPA]

POISSON'S

RATIO

YIELD STRENGTH

[MPA]

SS316L 193 0.25 170

NICKEL ALLOY 625 205 0.3 414

Figure 4 shows FE model of hub assembly which carries multiple loads like fluid pressure, bolt pretention, bending moment due to the stroke

tool force and end cap force(ECF). ECF is the effect of pressure in longitudinal direction.

Loads acting on hub assembly are shown in table 2,

TABLE II

LOADS ACTING ON HUB ASSEMBLY

Loads acting Unit Magnitude

Pressure N/mm2 4.5

End cap force N/mm2 5708

Bolt pretension N 21056

Bending moment N.mm 1750000

Stroke tool is placed between the notch of termination plate and porch plate. Porch plate is fixed with fixed boundary conditions and analysis

is done for calculating strength of termination plate.

Figure 5 FE model for termination plate assembly

Figure 6 FE model for support frame assembly

Plate of hollow cylindrical pipe is fixed and force is applied at point Rp-6 as shown in figure 5 and structural strength analysis is carried out on

support frame assembly.

V. EXPERIMENTATION

Testing of the tie-In connection system is carried out according to the ASME code section VIII. Tie in connection is tested for installation,

operating and testing loading conditions using stoke tool and hydraulic hand pump. Tie-In connection system with stroke tool attached can be seen

in figure 7.

Figure 7 Test rig and stroke tool

Termination assembly is lowered down by using chain block and guided by guide posts which rest on support frames. Support frames carries

the termination assembly load of 400 Kg. Now hubs are stroked together using stroke tool which has 1 KN load capacity and clamps are

tightened using clamp screw. Now test pressure of 4.5 bar is applied by hydraulic hand pump and maintained for 15 minutes after that pressure is

reduced to until it reaches to the value equal to the maximum allowable design pressure. A visual examination and liquid leak test is used to check

for cracks and leaks in all connections and welded joints. Design was safe under all loading and testing conditions also satisfies the ASME code

section VIII standards. Testing results obtained are agreed with physical reasoning and expectations.

VI. RESULTS

Finite element analysis of modelled parts is done using ABAQUS 6.13-4. The structural analysis is performed on hub assembly according to

the requirements stated in ASME VIII Div. 2 [5] and analysis of support frame assembly and termination plate assembly is done according to the

ISO 13628-7 BS 2005 standard [6]. Figure 8, figure 9 and figure 10 shows the FEA results.

Figure 8 Von-Mises stress distribution in the hub assembly

Figure 9 Von-Mises stress distribution in the termination plate assembly

Figure 10 Von-Mises stress distribution in the support frame assembly

Red circle indicates the area of the part where max von-mises stress is developed. For support frame and termination plate as loads are equally

taken by two same parts stresses developed are half of the value showing in the result. Analysis result shows that von-mises stress developed in

every part of the assemblies is below the yield value of the material hence all designs are safe for von-mises stress criterion.

VII. DISCUSSION OF RESULTS A. Von-mises stress

Table 3 shows von-mises stresses developed in the parts by FEM and analytical method. Von-mises stress generated in the clamp screw is

higher than other parts because of direct bolt load acting on the clamp screw. Von-mises stresses developed are less than yield stress of the

material hence parts are safe for von-mises stress criterion.

TABLE III

VON-MISES STRESS

Parts Material

Yield

stress

(N/mm2)

Analytical

(N/mm2)

FEM

(N/mm2) Test

Hub SS136L 170 103.5978 101.8

Safe as per

ASME VIII,

Division 2

criterion

Clamp Segment SS136L 170 89.235 94.5

Clamp

Screw

Nickel alloy

625 414 205.88 200.0

Support Frame SS136L 170 81.404 83.65

Termination

Plate SS136L 170 81.75 81.60

B. Global Criterion

Table 4 shown max local strain developed in each part is less than 2% hence satisfy global criterion for FEM and analytical both.

TABLE IV

LOGARITHMIC STRAIN (LE) DISTRIBUTION

Parts Material FEM (*e-4) Analytical (*e-4) Test

Hub SS136L 4.537 5.2725

Safe as per

ASME VIII,

Division 2

criterion

Clamp Segment SS136L 5.319 5.4338

Clamp

Screw

NICKEL

ALLOY 625 1.029 1.004

Support Frame SS136L 0.118 0.121

Termination Plate SS136L 0.124 0.09613

VIII. CONCLUSION

In this present work, hub assembly, support frame and termination plate of tie-in connection system were modelled on Solid Works software.

Finite element analysis was performed on ABAQUS software according to the ISO 13628-7 BS 2005 and ASME section VIII, Div-2 standards.

The plots of von-mises stress distribution, PEEQ and LE distribution were plotted and analysed. The finite element analysis showed that the

designed assemblies are safe. FEA results further validated by numerical calculation results. Testing was performed according to the ASME code

section VIII standard using hydraulic hand pump. Results obtained from analysis and experimentation shows tie-in connection system meets both

analysis and testing standards.

REFERENCES

[1] Chakrabarti, S., “Handbook of offshore engineering,” Volmes 1-2. Elsevier, 2005, pp. 1-34

[2] Yong Bai and Qiang Bai, Subsea Engineering Handbook, 1st Edition,: Elsevier, pp. 1-19, 571-701

[3] Qiang Bai and Yong Bai, “Subsea Pipeline Design, Analysis, and Installation

[4] Improved design rules for pipe clamp connectors, Cornelis J. Dekkera, Walther J. Stikvoortb, International Journal of Pressure

Vessels and Piping 81 (2004) science direct.

[5] Submarine Pipeline Systems, offshore standard DNV-OS-F101, October 2013

[6] ASME VIII, Div. 2 “Boiler & Pressure Vessel Code, Alternative Rules, Rules For Construction Of Pressure Vessels” july 1,

2015.

[7] ISO 13628-7:2005, “Petroleum and natural gas industries -- Design and operation of subsea production systems:

Completion/workover riser systems.”

[8] Ocean Engineering Series Volume 3, Elsevier 2001, Pages 305-323, Pages 305-323

[9] Christie, A. Kishino, J. Cromb et al., “Subsea Solutions,” 2000.