**4. Rehabilitation of pipe**

*Adhesives and Adhesive Joints in Industry Applications*

studied using SEM images as shown in **Figure 2**.

increases [20].

**3.4 Effect of surface texture**

surfaces can be seen in **Figure 8**.

adhesive bond strength increases [11].

*Load capacity of different pre-bond surfaces.*

**S. no Surface morphology Area fraction (%) Ra** 

squeezed out of the patch which increases the fibre volume fraction and reduces adhesive layer between SS plate and carbon fibre. Hence the adhesive bond strength

Surface preparation is very essential in adhesive bonding; a proper surface may provide a high bond strength. In order to find the proper surface to the adhesive bonding, the adherent surfaces were prepared with plane surface cleaned with acetone, chemical etched surface, sandblasted surface and surface texture created in the form of circular cavities at different densities with a depth of 80 ±5 μm as shown in **Figure 1b**. The surface roughness was measured using a 3D microscope, and the values can be seen in **Table 2**. The surface morphology of the samples was

The samples for tensile test was prepared with the optimal conditions like 100 mm bond length, 700 mm of Hg and 20% NSA + 80% SA mixture heated to 55°C. Tested results can be seen in **Table 2**. The specimens were failed by delamination between steel and carbon fibre interface (no residues of fibres). The failed

From the results, it was evident that the circular surface cavities spread over the 33% of the bonded area were shown a maximum bond strength of 14.15 kN, which is 26% higher than plane surface, 38% higher than etched surface and 12% higher than sandblasted surface. Surface texturing increases the surface roughness of the adherent which in turn increases the mechanical interlocking, and hence the

1 Circular cavities 10 8.81 13.35

2 Sand blasted 100 0.87 12.62 3 Plane sample 100 0.68 11.24 4 Etched surface 100 0.32 10.25

**(μm)**

25 20.73 13.83 33 27.08 14.15

**Load capacity (kN)**

**60**

**Figure 8.**

**Table 2.**

*Surface of the adherent after failure in tension test.*

The damaged SS pipes were considered for rehabilitation. The rehabilitation capacity was evaluated using hydrostatic pressure test. Here, a man-made through-all defect with 10 mm diameter was machined over an 200 mm diameter pipe. This through-all hole defect was covered with a two-component solid state adhesive (M-Seal). The pipe was tested for hydrostatic pressure with M-Seal adhesive after 24 hrs. A pressure of 500 ± 30 kPa was observed with M-Seal adhesive.

The pipe surface around the defect was prepared as plane surface cleaned with acetone, etched surface, sandblasted surface and sandblasted surface with circular cavities spread over 33% bonded area. The rehabilitation was done on defect filled with M-Seal adhesive; then the composite patch proposed during the present study as 100 × 100 mm bond area (the fibres in the adhesive bonding of SS plates are aligned in the loading direction with a length of 100 mm) with [0/90]3 carbon fibre layers, 700 mm of Hg and 20% NSA + 80% SA mixture heated to 55°C was applied.

These hydrostatic tests were conducted on the rehabilitated pipes as shown in **Figure 9**, and the results were given in **Table 3**. From the results, it is evident that the failure pressure of a pipe can be changed with surface texture. A maximum of 3852 ± 50 kPa was achieved with a pipe surface prepared with the combination of sandblasting and circular cavities. It is 62.8% higher than the plane surface.

#### **Figure 9.**

*Pipe hydrostatic pressure testing (left side) and surface prepared before patching (right side).*


**Table 3.** *Hydrostatic pressure of pipes.*
