Summary

Hot rolling mills use high-pressure water to remove oxide scale from steel before rolling. This process is called descaling. Its backbone is the high-pressure descaling piping that carries water from the pumps to the nozzles. This article explains how descaling works and what affects its performance. It also covers general requirements for pressure piping. Finally, it presents a case study: an upgrade of the main descale pump pipe by WCE’s MET business unit.

1. What Is Descaling and Why Does It Matter?

Steel reacts with oxygen while it is reheated before rolling. As a result, a layer of oxide scale forms on the surface. If the mill does not remove it, the rolls press the scale into the product surface [1]. In addition, the scale damages the surface and wears the work rolls [3]. For this reason, hot rolling mills install descalers with high-pressure water nozzles [1].

2. Key Principles of High-Pressure Descaling Piping and Water Jets

2.1 Jet Impact Is the Main Mechanism

A water jet hits the steel with two forces: impact and shear. Of these, impact force does most of the work. One study measured jet velocities above 130 m/s at a spray pressure of 20 MPa [2]. Impact rises with higher pressure and flow rate. However, it falls as the nozzle distance or spray angle increases [2].

2.2 System Pressures Are Very High

For example, one study of a hot strip mill descaler describes two header pairs. The front pair runs at about 21 MPa. Meanwhile, the rear pair runs at about 30–38 MPa [3]. Therefore, every pipe, fitting, and flange in the line must handle these pressures safely.

2.3 Nozzle Layout Affects Uniformity

A single nozzle cannot cover the full strip width. Consequently, the sprays must overlap. Poor offset angles leave more residual scale next to the overlap zones. The researchers suggest adjusting nozzle angles rather than raising water pressure, which wastes energy [1].

2.4 General Requirements for Plant Pressure Piping

ASME B31.3 Process Piping covers the full lifecycle of plant piping. It sets requirements for materials, design, fabrication, erection, examination, inspection, and testing [4]. In practice, repairs to high-pressure descaling piping therefore focus on weld quality, flange alignment, and pressure testing before restart.

3. Case Study: Main Pipe Descale Pump Upgrade by WCE MET

• Scope: Upgrade of the main high-pressure water pipe of an in-plant descale pump system
• Client: Leading steel sheet manufacturer in Thailand
• Duration: 1–7 September 2026 (7 days)
• Progress: 100% complete, on plan

This project drew on MET’s expertise in high-pressure water piping inside operating plants. First, the team removed the old pipe section. Next, it fabricated and welded a new spool and aligned the flanges. Finally, the team pressure-tested the line before handover. As a result, the descaling system returned to service in line with the production plan.

The cover image is a concept illustration. In the background, a perspective line drawing shows a pump room. On the right, a diagram traces the line from the pump to the main pipe. An orange highlight marks the new pipe section. A Detail: A cross-section and the four work steps complete the drawing. All images were created with AI assistance, so no person or client can be identified.

4. Lessons from This Project

Descaling directly affects steel surface quality. When it stops, the production line feels the impact. For this reason, maintenance on high-pressure descaling piping must fit the planned shutdown window. In addition, the work must be ready to hold operating pressure as soon as the system restarts.

5. WCE Services

WCE’s MET (Maintenance Engineering and Technology) business unit provides maintenance for industrial machinery and plant systems. Its services include installing and upgrading high-pressure piping.

Contact: +66 65-937-6283 | international@wce.co.th | www.wce.co.th
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References

1. Pohanka, M., Votavová, H., Resl, O., & Kotrbáček, P. (2023). The Effect of Water Jet Overlaps in a Descaler on the Quality of the Surface of the Hot-Rolled Steel. Metals, 13(10), 1722. https://doi.org/10.3390/met13101722 (accessed 28 October 2026)
2. Gongye, F., Zhou, J., Peng, J., Zhang, H., Peng, S., Li, S., & Deng, H. (2023). Study on the Removal of Oxide Scale Formed on 300 M Steel Special-Shaped Hot Forging Surfaces during Heating at Elevated Temperature by a High-Pressure Water Descaling Process. Materials, 16(4), 1745. https://doi.org/10.3390/ma16041745 (accessed 28 October 2026)
3. Zapata, O., Guerrero-Mata, M. P., & Colás, R. (2007). Simulation of Descaling during Continuous Hot Rolling. 2007 ABAQUS Users’ Conference. https://www.3ds.com/assets/invest/2023-10/simulation-descaling-continuous-2007.pdf (accessed 28 October 2026)
4. ASME. (2022). ASME B31.3-2022: Process Piping. American Society of Mechanical Engineers. https://www.csagroup.org/store/product/ASME%20B31.3-2022 (accessed 28 October 2026)