Length Measurement Methods for LSAW Pipe: A Complete Technical Guide

Accurate length measurement is a crucial part of LSAW pipe (Longitudinal Submerged Arc Welded pipe) production and quality inspection. Since LSAW pipes are widely used in high-demand industries such as oil and gas transmission, structural engineering, and offshore projects, ensuring precise dimensional control directly affects product performance and installation efficiency.
This article provides a comprehensive overview of the most common and effective LSAW pipe length measurement methods used in modern manufacturing.

1. Optical Grating Ruler Measurement

The optical grating ruler method is based on light interference principles. Two fixed-length grating rulers are installed at both ends of the LSAW pipe, and the rulers are driven by rods positioned near the pipe edges. The pipe length is then determined by analyzing the interference pattern of the reflected light.

Advantages:

· Extremely high measurement accuracy

· Suitable for precision manufacturing environments

Disadvantages:

· High equipment cost

· Sensitive to dust, vibration, and ambient light changes

· Requires regular calibration and maintenance

Although precise, this method is typically reserved for laboratory or high-value production lines due to its cost and complexity.

2. Camera-Based Optical Measurement

This technique uses image processing to determine the pipe length. A series of evenly spaced photoelectric switches are installed along the conveyor rollers, with a light source and camera placed at the opposite side. As the LSAW pipe passes through the detection zone, the system calculates its length by analyzing the captured images and corresponding light-switch signals.

Features:

· Enables real-time, continuous online measurement

· Suitable for high-speed production lines

· Reduces manual intervention

Camera-based systems are ideal for automated production environments where continuous monitoring and digital integration are required.

3. Encoder-Based Length Measurement

In this approach, an encoder is mounted on a cylinder that moves the pipe along the rollers. On the opposite side, a series of photoelectric switches detect the pipe’s movement. When the end of the pipe triggers the last switch, the system records the encoder’s displacement, which corresponds to the total length of the LSAW pipe.

Key Points:

· Reliable mechanical measurement principle

· Some measurement errors may occur due to sensor sensitivity

· Requires lifting the pipe during measurement

This method is common in mid-size fabrication facilities due to its simplicity and affordability.

4. Improved Encoder Measurement Method

This advanced method provides indirect length measurement. It uses two mobile measuring trolleys placed at both ends of the pipe. Each trolley has an encoder that records the travel distance between a reference point and each end of the pipe. The sum of these two distances gives the total pipe length.

Advantages:

· Eliminates interference from supports under the pipe

· Simple operation in complex industrial environments

· Measurement accuracy within ±10 mm and repeatability ≤5 mm

The improved encoder method is one of the most efficient and field-adaptable solutions for large-diameter LSAW pipe inspection.

Conclusion

Accurate length measurement ensures compliance with production standards and helps maintain pipeline integrity during installation.
Among these methods, manufacturers often choose based on factors like production scale, precision requirements, and cost.
Whether you are calibrating a new production line or improving inspection accuracy, understanding these measurement technologies will help ensure every LSAW pipe meets stringent engineering specifications.