Setting the Plate on Metal Plate

What is the difference between plate and sheet metal?

Determining the difference between metal plate and metal sheet comes down to one primary factor: thickness (also referred to as the gauge). And the magic number when it comes to thickness is 4.8 MM (.1889”)

Anything under 4.8 MM is metal sheet, while metal plate is anything thicker. Of course, the thicker the material the greater the weight added the application, which could be a concern for some.

Typically, though, those that are manufacturing applications that require plate are less concerned about weight and more about durability—i.e., bridges and construction equipment.

What is the difference between PMP and CMP?

Metal plate falls under one of two categories: PMP (plate mill plate) or CMP (continuous mill plate). For the record, CMP is also referred to as SMP (strip mill plate) in the carbon steel world.

The difference between PMP and CMP comes down to how it is produced.

CMP is made from a cast slab and rolled as a coiled product. In other words, think of a line of coil rolled out to which multiple pieces of plate are cut on a continuous basis. This produces widths of 48”, 60”, and 72” with a thickness range of .1875-.500”.

PMP is made from ingot and rolled one plate at a time. This method helps achieve larger widths of 84”, 96”, and 120” with a thickness range of .1875-6”.

Do all grades come as both PMP and CMP?

For stainless steel, most common grades like 304, 316, and 201 are made in both CMP and PMP, varying simply by thickness.

It’s a different story in the carbon steel world. While several common grades, including A36, 516-70, Grade 50, can be made as both PMP and CMP, other grades like A514 and API2H50 are generally only produced as PMP.

When to use PMP vs. CMP?

Here are a few factors to consider when determining which applications call for what type of metal plate.

Fabricated parts: Knowing that PMP can achieve larger widths, this is usually the preferred type of metal plate should the application call for some degree of fabrication. 

Welding: Would the integrity of your application be compromised by welding multiple pieces together (CMP)? If so, PMP would be a better fit as they are generally produced at greater dimensions.

Availability: This is a consideration given the fact that not all steel mills produce the same volume of both PMP and CMP. This factor has become magnified given the lower capacity utilization rates and other market factors that are causing a tightness in supply. 

Jim Reed, Ryerson’s senior product manager, supply chain, highlights how current market conditions are creating a unique situation for stainless steel plate.

“In the stainless world there are really only two domestic mills that make plate mill plate—one of which is currently on strike. But there is a third if consider the fact that NAS (North American Stainless) calls their discrete plate PMP, and that is because it is thicker than 3/8”. Normally it is going to be like ½” to 2 ½” x 48” or 60” wide because those come out of a slab, not a coil.”

Cost: Here is where the script has flipped a bit as of late. In normal times, PMP is more expensive than CMP due to the extra steps involved with making it when compared with CMP. But with regards to carbon steel, that hasn’t necessarily been the case as of late.

Mark Gross, Ryerson’s senior product manager, carbon flat roll supply chain, explains: “In normal times, PMP is more expensive than SMP (CMP), but that trend has flipped at a substantial rate lately due in large part to the fact that the prices of sheet is so high these days. Another factor is that certain plate mills will share production lines with sheet mill plate, and since the sheet mill plate is more profitable to produce, given current conditions, they will choose to prioritize making that over PMP.”

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