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Summary: Offshore wind tenders from CNOOC (500 MW, 28 units of 18 MW) and Guangdong Energy Group (1,130 MW across three projects) landed within two weeks of each other. Tower shells, monopiles and jackets are all blast-cleaned onshore before coating. This article walks through the mix used on thick-walled rolled plate, tight inner shells and flange faces.

Two large offshore tenders in two weeks

On September 30, Guangdong Wind Power released a bundled tender covering Gaolan II, Xuwen Dongyi and Xuwen Yangqian, split into five lots totaling 1,130 MW. Gaolan II accounts for 500 MW with 36 planned turbines of 14 MW in water 31 to 35 m deep. Xuwen Dongyi adds 400 MW with 29 units of 14 MW. Xuwen Yangqian is a repowering scheme that removes 33 turbines of 1.5 MW from a site commissioned in May 2009 and installs 17 units of 13 MW and above.

Then on October 10 came the CNOOC tender for Shanwei Red Bay IV: 500 MW, 28 units of 18 MW class, water depth of 34 to 43 m.

Why thick rolled plate is harder to blast than flat plate

Tower shells are rolled from plate that runs 20 to 40 mm thick. Mill scale on hot-rolled heavy plate bonds tightly to the surface, and by the time the steel reaches the blasting line it usually carries a rust layer on top of it.

Two requirements pull in opposite directions. Stripping scale quickly calls for larger particles and higher impact energy. Producing an even profile across the whole surface calls for finer particles. Run a single size and one of the two suffers. The targets engineers normally work to are Sa2.5 cleanliness and Rz 75 to 100 μm.

Three zones, three mixes

Outer shell. S460 alloy cast steel shot does the stripping work first. Angular steel grit follows to cut the profile. A shot-to-grit ratio of 7:3 is the usual starting point and is adjusted for plate thickness.

Inner shell. Working inside the shell leaves little clearance. The blast wheel cannot reach every corner, and fine control matters more than raw impact. S330 is the practical choice here, because larger media tend to over-blast the edges without reaching the interior.

Flange faces. These are mating surfaces and must stay fine. Finish with a smaller shot size and keep angular grit off them entirely, so the mating faces do not pick up scratches that show during assembly.

Controlling profile on every batch

Abrasive recirculates inside the machine and breaks down as it works, so particle size distribution drifts on its own. A single-size charge will hold profile for a while and then start to wander.

Grading solves this. Several shot and grit sizes are blended in proportions calculated from the workpiece material, plate thickness, machine parameters and target profile. On the same machine, a graded charge holds Sa2.5 and Rz 75 to 100 μm across a run, which lifts the first-pass acceptance rate.

Our corporate standard Q/HX 001-2026 caps non-spherical particles at 5 percent, holds sulfur and phosphorus below 0.03 percent, requires density of at least 7.4 g/cm³, and specifies a cyclic life of 2,200 cycles or more.

The cost that matters is consumption, not price per tonne

A cheap abrasive looks good on the purchase order and expensive on the shop floor. Higher breakage means more fines and more material fed for the same area. On a wind tower order that runs for months, a 30 percent gap in consumption outweighs a small difference in unit price, and that is before rework costs from a failed profile check.

Wind installation windows do not negotiate. One day lost on the blasting line moves coating, shipment and lifting back with it. We keep 28 warehouse bases across China with 72-hour delivery on standard grades and same-day dispatch in Hubei and surrounding provinces. S330, S390, S460, S550 and 1.0 cut wire shot are held in stock, and every batch ships with an inspection report.

Wuhan Hongxin Lixin Metal Products Co., Ltd. (Mali Steel Shot brand) — 25 years in metallic abrasives, producing alloy steel shot, stainless steel shot, cut wire shot and angular steel grit to GB/T 18838.4, SSPC and ISO 9001. Website: http://www.sisball.com/ . Hotline: 400-038-8928.