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Double your money with zirconia ceramics in oil and gas - part one

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Oilfield Technology,

Ray Mouw, Morgan Advanced Materials, explains why magnesia stabilised zirconia ceramic components will be vital for pumps that work in harsh environments, such as oil and gas, and crude oil extraction.

It goes without saying that crude oil is a valuable, or perhaps more accurately an invaluable product to all of us globally. The unrefined petroleum is pumped from reserves deep underground and by the barrel load, all day, every day.

Our dependence on this product (which is processed into a variety of fuel sources and commodities like jet fuel, petrol and diesel) has been quantified by a market intelligence report from Beroe.

In terms of demand and supply, the global fuel oil supply stands at 92.7 million bpd, while the global fuel oil demand stands at 98.18 million bpd. Demand is expected to increase, with a compound annual growth rate (CAGR) of 1.8%, until 2020. For all the efforts being put into renewable and alternative energy sources, the reliance on crude oil will not go away any time soon.

It is clear that investment, innovation and operational best practice must continue into the extraction of crude oil. Otherwise, supply slows down and the price per barrel of crude oil then increases due to the imbalance.

A key component that helps to keep supply up are pumps. Unlike the slick and smooth products that it is turned into, crude oil is a petroleum composed of hydrocarbon deposits that ranges in viscosity, and contains oil, water and sand (often as the wells dry out increasingly) in its natural form.

Therefore, the pumps undertaking the extraction need to be durable and able to withstand the harsh, abrasive sandy oil. The first challenge is ensuring these costly pieces of equipment have a long lifespan, as only then can true value be achieved.

Striking it rich with heavy duty pumps

As would be expected, pumps on oil rigs are an expensive outlay. Not only are there energy costs to run the pump, but the capital and maintenance costs are high.

Typically, a ‘clean oil’ pump – that is, a pump which is pumping purer crude oil – will last ten years between overhauls. However, with a sandy, dirtier crude oil, the pump life deteriorates in as little as one year. The reason for these high maintenance costs is largely down to the erosion caused on the impeller shafts and wear rings (from the sand in the crude oil). It is the rapid wear through the tight wear ring clearance points that determines when the pumps are overhauled.

The materials used to construct these parts are various grades of metal often coated with wear resistant sprays. When pumping, pressures range from 2100 kpa during suction up to 15 000 kpa during discharge. These pressures, combined with the rough surfaces of the sand, will quickly erode wear rings and bearings. In turn, the pump becomes less effective and inefficient.

While it may be easy to accept that this is just the norm of how heavy-duty pumps are constructed, there is an alternative to using hardened stainless-steel components. Parts made from magnesia stabilised zirconia (also known as MgPSZ) ceramic are fast becoming the preferred alternative.

Of the various grades of zirconia ceramic available on the market, it is the magnesia partially stabilised grade that is best suited to heavy duty pumps. Unlike other grades of zirconia ceramic, such as yttria stabilised zirconia, magnesia stabilised zirconia is the toughest, most reliable grade and is not affected by hydrothermal degradation - an important criterion in moist, elevated temperature environments.

Morgan Advanced Materials’ Nilcra® Zirconia is one such grade of magnesia stabilised zirconia and is a robust and simple to use replacement material for applications where high wear rates occur. By using this type of zirconia ceramic, the time between overhauls for a sandy crude oil pump can increase from the typical one-year lifespan up to four to six years instead.

Indeed, an example of this bettered performance has been seen by Morgan when comparing a refurbished eight-stage centrifugal pump, fitted with Nilcra Zirconia wear rings and shaft bushings, across a four-year period.

Wear rings for centrifugal multistage pump.

OEM wear rings fitted to the pump’s impeller shaft were made from 420 stainless-steel 270-300 BHH and 420 stainless-steel 350-400 BHH. These wear rings lasted 12 - 15 months in a sandy well service, before requiring a total overhaul.

Meanwhile, wear rings made from Nilcra Zirconia were also fitted to a different section of the impeller shaft. Findings showed a huge decrease in the wear on the magnesia stabilised zirconia rings in comparison to the spray-coated stainless-steel rings. The life of the pump was extended by approximately four times as a result, with reduced downtime and maintenance costs resulting in an increase to production.

Multistage centrifugal pump retrofitted with ceramic wear part. Courtesy of United Pumps Australia.

A slicker operation

Just off the south coast of Australia is where magnesia partially stabilised zirconia ceramics have proven to be successful, following Morgan’s consultation.

In this region up to 480 000 bbl, or 76 800 m³ of crude oil is pumped per day, with nearly 40 pumps in use across the site since the 1990s.

However, the operation and maintenance of the pumps is costly. Sand content within the crude oil in the wells has been steadily increasing as oil reserves have been dwindling down over time. It was found that each pump would only be able to provide roughly one year of service before needing critical maintenance from wear and erosion.

Crucially, wear was happening in four key areas of the pumps. Namely, these were the throttle bush, case separating ring, throat bush and impellor wear ring, which were made from hardened stainless steel or coated stainless steel.

Following the site operator’s consultation with Morgan Advanced Materials, these parts were replaced with Nilcra Zirconia, with only slight modifications to the internal corner radii to reduce corner stresses and facilitate diamond grinding wheels. Over 40 pumps have been retrofitted, and lifespan for each pump has increased from the typical one-year lifespan to an estimated four to six years instead.

Author: Ray Mouw, Morgan Advanced Materials
This is part one of a two-part article. Part two can be read here.

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