What Is 3-Roll RBE?

1. Edge Preparation

Before any bending takes place, the steel plate must be properly prepared. Heavy steel
plates are usually cleaned, inspected and checked for surface or internal defects.
Ultrasonic testing may be used depending on the project specification.

Milling

Edge milling machines prepare the two longitudinal edges of the plate. The edges are
machined into a precise welding groove profile, such as a V-groove,
double-V groove or double-Y groove.

The bevel angle may be designed according to the welding process and pipe specification,
for example 30° or 37.5°, together with a controlled
root face.

Tolerances

Accurate edge preparation is essential. The two edges must remain parallel, and the
plate width tolerance must be tightly controlled. If the edge geometry is not accurate,
the later forming, seam closing and welding processes may suffer from poor alignment,
uneven root gap or excessive high-low mismatch.

2. 3-Roll Bending and Edge Crimping

The RBE process forms a flat plate into an open cylindrical shell without using massive
diameter-specific press dies. This makes it different from JCO or UOE forming routes.

3-Roll Bending

The prepared plate is passed through a hydraulic three-roll bending machine. The rolls
apply controlled and adjustable pressure to gradually bend the plate into an open
cylindrical shape.

During this process, the plate is progressively curved into an open U,
O or cylindrical form, depending on the forming stage and machine setting.

Reverse Edge Crimping

A common limitation of traditional three-roll bending is that the extreme longitudinal
edges of the plate may remain relatively flat. These flat edge zones can affect seam
closing, weld fit-up and final pipe roundness.

To solve this problem, the open shell is sent to a crimping or reverse-bending machine.
This equipment bends the plate edges in the opposite direction so that the edge radius
matches the radius of the pipe body. This step helps eliminate flat spots near the weld
seam area.

3. Seam Closing and Fit-Up

After roll bending and edge crimping, the two longitudinal edges of the open pipe shell
must be brought together and fixed before the main welding process.

Closing

Heavy-duty clamping fixtures, fit-up rolls or hydraulic closing devices are used to pull
the longitudinal edges together. The goal is to create a stable seam condition before
welding.

Fit-Up and Tack Welding

Good fit-up is one of the most important quality factors in LSAW pipe production. The
root gap must be uniform, and internal or external high-low misalignment must be kept
within the project tolerance. In many pipe specifications, the high-low mismatch is
strictly controlled, for example less than 1.6 mm, depending on the
standard and wall thickness.

The pipe shell is held in position by fit-up rolls or clamping devices. Tack welding,
often using GMAW or MIG welding, is then applied along the longitudinal seam to hold the
shell together before the main submerged arc welding stage.

4. Welding Process

The main weld is usually completed by Submerged Arc Welding, also known
as SAW. This welding method uses a granular flux to protect the arc and
molten weld pool, producing a deep, stable and high-quality weld.

For LSAW pipe production, welding is normally performed on both the inside and outside
of the pipe. Depending on the pipe size, wall thickness and productivity requirement,
single-wire or multi-wire SAW systems may be used.

The welding process must be carefully controlled to ensure weld penetration, weld bead
shape, mechanical strength and compliance with the applicable pipe standard.

5. Pipe Support and Handling

During tack welding, internal welding and external welding, the pipe must be accurately
supported and rotated. Specialized pipe handling systems are therefore required.

These systems may include motorized rollers, adjustable pipe supports, transfer cars and
alignment systems. Their purpose is to keep the pipe stable and correctly positioned
during welding, inspection and transportation between process stations.

6. Full-Body Expansion

After welding, the pipe may go through a mechanical full-body expansion process. The
expansion machine applies controlled radial force from inside the pipe to slightly expand
the pipe body.

This process helps improve pipe roundness, reduce dimensional deviation and relieve part
of the residual stress generated during forming and welding. For high-specification LSAW
pipes, expansion is often a key process for achieving final dimensional accuracy.

7. Typical Process Flow of 3-Roll RBE

8. Main Equipment Used in a 3-Roll RBE Line

9. Why Use the 3-Roll RBE Route?

The 3-roll RBE route can be useful when pipe manufacturers need flexible production for
different pipe diameters without investing in a complete set of diameter-specific forming
dies.

• Suitable for large-diameter longitudinal welded pipe production
• More flexible for different diameters compared with die-based forming routes
• Can reduce tooling cost for certain production ranges
• Combines roll bending flexibility with expansion-based dimensional correction
• Can be used for customized pipe production and project-based pipe manufacturing

10. 3-Roll RBE vs. Standard Plate Rolling

In ordinary plate rolling applications, the goal is usually to roll a plate into a cylinder
or cone for tanks, vessels or general fabrication. In 3-roll RBE pipe production, the goal
is much more demanding. The formed shell must meet strict requirements for seam alignment,
roundness, weld quality and final pipe tolerance.

Therefore, when evaluating a 3-roll solution for pipe production, buyers should not only
ask for the price of a rolling machine. They should also confirm the complete process
route, including plate preparation, edge crimping, fit-up, welding and expansion.

Conclusion

The 3-roll RBE process is a flexible forming route for producing
large-diameter LSAW pipes. It uses three-roll bending as the main forming method, while
relying on edge crimping, accurate seam fit-up, submerged arc welding and full-body
expansion to achieve the final pipe quality.

For buyers considering this process, the most important question is not only whether the
plate can be rolled, but whether the complete forming and welding route can meet the
required pipe diameter, wall thickness, roundness, seam quality and final application
standard.