Strength analysis of adhesive joints of riser pipes in deep sea environment loadings
© Zhang et al.; licensee Springer. 2013
Received: 2 September 2013
Accepted: 30 October 2013
Published: 30 December 2013
Nowadays, adhesive joints are widely used in riser pipes, which are subjected to many kinds of loadings in deep sea, such as external pressure, internal pressure, tension, torsion, bending, and also a combination of these loadings. Adhesive joints of riser pipes are the most dangerous parts in term of strength, as singular stress fields exist at the end of the interface between the adhesive and the adherends, so it is very important to evaluate the strength of adhesive bonded joints for riser pipes in deep sea environment loadings. In this research, the strength of adhesive joints of riser pipes is studied under external pressure, internal pressure, tension, torsion, bending loadings, and it is found that singular stress fields exist around the end of the interface. The riser pipe under external pressure, internal pressure and tension loading is more prone to break than under bending and torque loading.
Due to low manufacturing costs, low stress concentration and ease of maintenance, adhesive joints are most frequently used in numerous industrial sectors such as automobile, shipbuilding, aeronautical, etc., replacing or supplementing traditional joining technologies, such as welding or riveting. Adhesive bonded joints are also widely used in riser pipes because of their light weight, high strength, and high corrosion resistance. With the wide use of adhesive joints, many research works have been done to evaluate their strength including experimental and analytical methods [2–8].
The mismatch of different materials properties may cause stress singularity at the end of the interface between different materials, which leads to failure of the bonding part in structures, so it is very important to analyze the stress singularity field for evaluating the strength of adhesively bonded joints. Many researchers did some valuable work to analyze the stress singularity field at the end of interface between the adhesive and the adherends, such as Koguchi et al. , Kilic et al. , Van Tooren et al. , and Goglio and Rossetto , Tilscher . Zhang  proposed one easy method to evaluate the effect of adhesive thickness and length on the strength of adhesive joints. Moreover, Zou and Taheri  analyzed stress distributions of adhesive bonded sandwich pipe joints subjected to torsional loadings. Da Silva et al. made a detailed and comprehensive comparion between studies about adhesively bonded joints [16, 17].
Here r, θ are the polar coordinates around the interface edge, a, β are Dunders’ parameters which are expressed by Possion’s ratio v and shear modulus G.
In this paper, the scaling model with the following dimensions was used: adhesive thickness h0 = 6 mm, cover thickness h1 =10 mm, total length 2 L = 200 mm and coupling length 2c = 25 mm. The outer diameter of the adherend was 140 mm and the inner diameter was 110 mm. The adherend steel elastic properties were E = 70,000 MPa, v = 0.33. The adhesive material elastic properties were E = 3500 MPa, v = 0.30, which means that the existence of singular stress fields condition a(a-2β) > 0 is satisfied at the edge of interface between adhesive and adherend.
The commercial software ABAQUS was used to perform the analysis. The finite element method model was constructed using 3-D solid elements (Figure 3). Two mesh densities were used to conduct the analysis. A coarse mesh with the mesh density of 32 rows of elements circumferentially 2 rows (radially) · 30 rows (axially) was used to model the pipe region, while the mesh density was doubled to model the joint region. Moreover, the mesh of the joint region was graded along the axial direction of the pipe, finer toward the free edges of the joint.
Results and discussion
External pressure loading case
Internal pressure loading case
Generally, the internal pressure of a riser pipe is higher than the external pressure to prevent buckling of the pipe, and in this research, an internal pressure P ip = 15.0 MPa was chosen. The boundary conditions for this case were: u r = 0, at x = 0; u x = 0, x = 0; and u s = 0, x = 0.
Tension loading case
Bending loading case
Torque loading case
Comparison of stress intensity fields between the cases of external pressure, internal pressure, tension, bending and torque loading
Stress values at the end of the interface are related to the element sizes, and models under different loading cases have the same mesh sizes in this paper. From the comparison, it can be said that different loading cases have different gradients of stress lines. The gradient of stress lines indicates the index of the singular stresses singularity at the end of the interface. If the loading values increase, the stress values at the end of the interface will also increase, without changing the gradient of the stress lines. So the gradients of stress lines are only related to the loading conditions if the mesh sizes do not change.
In this paper, a 3D adhesive joint model was constructed using FEM, and the singular stress field around the end of the interface between the adhesive and the adherend was analyzed for cases of external pressure, internal pressure, tension, bending and torque loadings. Singular stress fields exist for all the loading cases, and the stress singularity is larger for cases of external pressure, internal pressure and tension loading compared to the cases of bending and torque loading, which means that the riser pipe under external pressure, internal pressure and tension loading is more prone to break than under bending and torque loading in deep sea environment.
The authors appreciate the reviewer’s constructive comments and detailed feedback for improving the manuscript. This research was supported by Science Foundation of China University of Petroleum, Beijing (No. 2462013YJRC44), and the National Basic Research Program of China (973 Program) Grant No. 2011CB013702.
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