UHP Graphite Electrode

UHP graphite electrode are mostly made of 100% high-specification needle coke. Compared with HP and RP grades, UHP electrode requires highest technical expertise in each of the main process steps in making them, particularly baking, extrusion and graphitizing.

Features

The electrodes come with a wide range of sizes, but diameter of  600mm and 700mm high performance. UHP graphite electrode is often used for ultra high power electric arc furnaces (EAF) with current density greater than 25 A/cm2.

The length of EAF graphite electrodes can be up to 2900mm. They are usually packed with pre-set graphite nipple, which allows one electrode to be joined together with another. In an EAF, three electrodes are often joined together to form a column, with new electrodes added to the top of a column as electrodes are consumed upwards from the tip. In a DC furnace, one column is used, but in an AC furnace three columns are used simultaneously.

The rate at which UHP graphite electrodes are consumed in an EAF depends on the steelmaking or other raw materials used, the grades of steel being produced, and the amount of supplemental (chemical) energy used. EAFs typically consume electrodes at a rate of around 2 kg per tonne of steel produced, with some specialty steel applications consuming at a slightly higher rate.

Hgraphite’s focus is being a very good partner with the steel industry and to foster long-term relationships with clients, delivering products to customers when and where they want them at a fair price.

Ultra-high-power (UHP) electrodes are often found inside of electric arc furnaces, or EAFs, which are used in most metal shops. Capable of reaching extremely high temperatures to melt even some of the hardest metals, ultra-high-power (UHP) electrodes play a vital role in melt-shop operations, yet they have never received that much attention when it comes to relevant markets, at least not until 2018.

UHP electrodes are made using many different materials, including petroleum coke, needle coke, and coal pitch. There are many steps to the production process.

Following calcination, the UHP must be kneaded, pressed, roasted, graphitized, machined, and finally released into an electric arc furnace (EAF) for the steelmaking process to begin. Graphite electrode quality is indicated by the name, ranging from ordinary power graphite electrode (lowest quality) to HP graphite electrode (mid-quality) to UHP graphite electrode (highest quality).

A few years back, the steel industry noted a shorted of UHP graphite electrodes and, as expected, the lack of supply in the face of imminent demand drove the prices up to critical highs. Meanwhile, steelmakers tried to secure a steady source of UHP to avoid production holdups. Of course, not every steel producer was able to do so, and many some steel production was slowed or halted until producers could secure more UHP.

Reportedly, the panic led to UHP electrode prices peaking at up to $30,000 per tonne. However, prices have since fallen, although they remain high when compared to the historical cost of UHP. Meanwhile, the global demand for UHP is estimated at around 785,000 tonnes per year. This has kept steel producers on their toes, since the global demand is very near to the annual global production capacity of 800,000 tonnes.

While China is capable of producing approximately 50,000 tonnes on top of the above estimate (and perhaps even more if they lower the quality), the current state of UHP electrodes is still on the edge. Today, the supply and demand equation for UHP remains in a careful balance, which is a far cry from the state of the market some years ago.

Back when the world steel markets were performing exceedingly poorly, UHP was in very low demand, and about 20% of UHP production stopped as a result of that. This is what experts say led to the unexpected shortage the markets witnessed just a few years back. However, although demand has picked up, UHP production remains bridled in light of materials shortages.

Needle coke is one such critical ingredient in the production of UHP that UHP producers are struggling to find. Experts estimated a global production of no more than 900,000 tonnes per year for this ingredient, and producing 1 tonne of UHP consumes about 1 tonne of needle coke.

With the most recent estimated need for UHP sitting at 820,000 tonnes per year (implying a 5% annual increase in demand), producing needle coke at full capacity is a critical element in avoiding another shortage. As we enter 2020, it awaits to be seen just how the market turns out for UHP production and its components.

 

Technical Specification of UHP Graphite Electrode

Item Dia 300-400mm Dia 450-500mm Dia 550-650mm Dia 700-800mm
Electrode Nipple Electrode Nipple Electrode Nipple Electrode Nipple
Specific Resistance ≤6.2µΩm ≤5.3µΩm ≤6.3µΩm ≤5.3µΩm ≤6µΩm ≤4.5µΩm ≤5.8µΩm ≤4.3µΩm
Bending Strength ≥10.5Mpa ≥20Mpa ≥10.5Mpa ≥20Mpa ≥10Mpa ≥22Mpa ≥10Mpa ≥23Mpa
Elastic Modulus ≤14Gpa ≤20Gpa ≤14Gpa ≤20Gpa ≤14Gpa ≤22Gpa ≤14Gpa ≤22Gpa
Bulk density ≥1.67g/cm³ ≥1.74g/cm³ ≥1.66g/cm³ ≥1.75g/cm³ ≥1.66g/cm³ ≥1.78g/cm³ ≥1.68g/cm³ ≥1.78g/cm³
CTE  (100-600℃) ≤1.5*10^-6/℃ ≤1.4*10^-6/℃ ≤1.5*10^-6/℃ ≤1.4*10^-6/℃ ≤1.5*10^-6/℃ ≤1.3*10^-6/℃ ≤1.5*10^-6/℃ ≤1.3*10^-6/℃
Ash ≤0.2% ≤0.2% ≤0.2% ≤0.2% ≤0.2% ≤0.2% ≤0.2% ≤0.2%

UHP Graphite Electrode Sizes & Tolerance

Diameter (mm) Length (mm)
Nominal Diameter Actual Diameter Nominal Length (Options) Tolerance
(inch) (mm) (max.) (min.)
8 200 205 200 1600 ±100
9 225 230 225 1600
10 250 256 251 1600/1800
12 300 307 302 1600/1800
14 350 357 352 1600/1800
16 400 409 403 1600/1800/2000/2200
18 450 460 454 1600/1800/2000/2200
20 500 511 505 1800/2000/2200/2400
22 550 562 556 1800/2000/2200/2400
24 600 613 607 2000/2200/2400
26 650 663 659 2000/2200/2400/2700
28 700 714 710 2000/2200/2400/2700
30 750 765 761 2000/2200/2400/2700
32 800 816 812 2000/2200/2400/2700

Suggested Current-Capacities of UHP Electrodes

Nominal Diameter Suggested Current-Carrying Capaities (A) Current  Density(A/cm2)
mm inch
300 12 15000-22000 20-30
350 14 20000-30000 20-30
400 16 25000-40000 19-30
450 18 32000-45000 19-27
500 20 38000-55000 18-27
550 22 45000-65000 18-27
600 24 48000-56000 14-24
650 26 60000-85000 18-25
700 28 70000-120000 18-30

Surface Quality

Item Defect Dimension Nominal Diameter of Graphite Electrode
300–400mm 450–600mm
Diameter (mm) 20–40
(< 20 mm should be negligible)
30–50
(< 30 mm should be negligible)
Depth (mm) 5–10
(< 5 mm should be negligible)
10–15
(< 10 mm should be negligible)
Remarks:
1. There should be less than two defects or holes on the electrode surface, the max size of which is mentioned in the above chart.
2. There should be no transverse crack on the electrode surface. For the longitudinal crack, the length should be less than 5% of the electrode circumference and the width in between 0.3-1.0mm.
3. The width of black area on electrode surface should be less than 1/10 of electrode circumference and the length less than 1/3 of electrode.