Hot tapping is a mechanical process commonly encountered in piping and pipeline systems. Hot tapping aims to attach fittings/branches/connections without ceasing the operation of the piping system, thus, the hot tapping process is selected when the piping system can’t be shutdown. Compared to another process such as the cold cut, the hot tapping process avoids the loss of company’s revenues and environmental issues due to the seepage of gas to the atmosphere.
Hot tapping process consists of several stages which can be seen in figure 1. In essence, this process entails the machine to drill the piping system. Figure 2 exhibits the assembly of mechanical parts utilized during the hot tapping process, as aforementioned this machine cuts the pipe, hence, the additional fitting could be mounted.
Figure 1. Hot tapping process (Rosman, 2017)
Figure 2. Assembly of mechanical parts used in the hot tapping (Rosman, 2017).
The hot tapping is categorized as a critical process (Nasution 2022), thereby, critical assessments must be done in advance to ward off the likelihood of failures. There are 3 types of failures during the hot tapping process which are Burn Through, Hydrogen Induced Cracking, and Chemical Reaction (Rosman, 2017). Detail explanations are provided below
1. Burn through
Welding process during the hot tapping produces heat that affects the integrity of the piping system, thus, before conducting the welding process in-service welding analysis could be conducted, to assess the temperature of pipe, stress, and strain (Tambunan et al 2019). Figure 3 exhibits the excess of temperature due to the welding process that might lead to the loss of mechanical strength of the piping material, subsequently the piping system is prone to experience localized ruptured due to the fluid pressure during the operation. Therefore, the leakage probably occurs afterwards.
Figure 3. Temperature of a pipe connection due to the hot tapping welding process (Asl, H. M 2013)
2. Hydrogen Induced Cracking
Since the hot tapping process is conducted when the piping system is operated, then the heat transfer phenomenon namely convection inevitably emerges. In which, the flowing fluid acts as a heat transfer medium which carries the heat stems from the welding process.
When, the heat on the heat affected zone (HAZ) is dissipated rapidly, then this can alter and reduce the mechanical strength of the pipe. 2 pipe conditions occur due to this rapid cooling rate (Rosman, 2017), firstly the pipe tends to lack of corrosion resistance, and secondly the reduction of material toughness because of the formation of hard microstructures and creep which are brittle and hard at the affected region.
One of the ways to overcome this failure is by conducting the Post Weld Heat Treatment (PWHT) after the welding process which can be seen in figure 4, thus, the strength of pipe’s material can be increased and the residual stress can be dwindled (Patel et al 2018), hence PWHT can prevent the possibility of rupture in the future.
Figure 4. Post Weld Heat Treatment Process (Patel et al 2018),
3. Chemical reaction leading to explosion
Lastly, the interplay between the fluid and the inner pipe wall surface in the high temperature environment may produce explosion. Thus, further assessment and analysis regarding this relationship has to be done properly before constructing the hot tapping process.
REFERENCES
Asl, H. M., & Vatani, A. (2013). Numerical analysis of the burn-through at in-service welding of 316 stainless steel pipeline. International Journal of Pressure Vessels and Piping, 105-106, 49–59.
Nasution, S.Y., Prasojo, B., Wismawati, E., So’im, S., Ari, M. (2022). Hot Tapping Process Analysis On Gas Distribution Pipes Online Services Using Shielded Metal Arc Welding. Politeknik Perkapalan Negeri Surabaya. Journal Welding of Technology
Patel, A.R., & Acharya, G.D. (2018). Effect of Post Weld Heat Treatment on Mechanical Properties and Microstructure of P 11 Weld : A Review.
Rosman, M, A, B. (2017). Temperature Prediction in Hot Tapping Process for High Pressure Pipeline. Universiti Teknologi Petronas.
Tambunan, S., Yatim, A., Sanjaya, P, W., Simon, M. (2019). In Service Welding Simulation of 28” Pipeline using Finite Element Method. PT 3S Engineering. IOP Conf Series: Materials Science and Engineering.
Muhamad Alim 
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