What should be done to the surface of the steel pipe before installing a bolted coupling?

Before installing a bolted coupling on a steel pipe, it is essential to remove oil, dirt, loose scale, and rust from the surface of the pipe. This preparatory step ensures that the coupling can create a proper seal and fit securely, which is critical for the integrity and functionality of the pipeline system. Any contaminants or irregular surfaces can interfere with the coupling's ability to clamp down effectively, potentially leading to leaks or failures in the joint.

Proper surface preparation also aids in preventing corrosion and extending the lifespan of the installation. Clean surfaces allow for better contact between the coupling and the pipe, providing a stronger bond. Additionally, ensuring the removal of rust not only enhances the aesthetic aspect of the installation but also guarantees that there are no weak points that rust can create once the coupling is in place.

While applying a protective coating, marking the end for insertion depth, and checking the inner coupling for debris are all important steps in pipeline assembly and maintenance, they serve different purposes that do not address the immediate need for a clean surface on the pipe before coupling installation.