g systems with small, abrasive sponge-like balls to keep the tubes clean and test for tube defectives with probing devices. Tube thinning and corrosion create the opportunity for tube leakage. This can not be tolerated because chemicals such as sodium and chlorides find their way into the reactor vessel or steam generator.

Upgrading the steam condenser tubing to stainless steel also plays a vital role in the ‘power uprate’ program utilities have used to increase generating capacity for existing reactors as we recently discussed. The more advanced uprate program could add up to 20-percent capacity to existing U.S. nuclear reactors.

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Molybdenum plays a more vital role in the global nuclear renaissance than you might suspect. Without the silvery white metal, the world’s energy infrastructure would somewhat suffer. But, nuclear power plants would be set back at least two decades. The new high performance stainless steels (HPSS) contain as much as 7.5 percent molybdenum and can add more than three times the life to the world’s aging nuclear fleet condenser tubes.

During the early construction of nuclear power plants, steam condensers relied upon copper base alloys – brass and copper nickel – for heat transfer capabilities. These alloys have high coefficients of thermal conductivity required in steam generation to power nuclear reactor turbines. But copper-alloyed tubes were being replaced too quickly – with an average life of eight years – because of sulphide pitting. Hardest hit were those reactors using polluted seawater to cool their reactors.

Over the past 30 years ago, nuclear utilities slowly began turning to the super austenitic stainless steels as one way to make their nuclear reactors last longer. The addition of molybdenum, initially starting with percentage of less than four percent, helped increase the thermal conductivity lacking in nickel, iron or steel. At nuclear stations which replaced the copper alloys with HPSS condenser tubes, 57 percent rated the thermal performance good and all but one rated it normal. Molybdenum had helped overcome the thermal hurdle.

A large number of the 190 nuclear reactors, which now utilize HPSS condenser tubes, reported an average life in excess of 18 years. The longest stainless steel condenser installation has remained in service more than 26 years, according to a study done several years ago. According to a report published in 2000, more than 100 million feet of super-alloy stainless steel tubes have replaced the older, copper-alloy tubing.

Condensers are large heat exchangers used in nuclear power plants. Condensers have thousands of tubes horizontally mounted to condense and recover the steam passing through turbines. Each low-pressure turbine generally has a condenser, which also maintains a vacuum to optimize the turbine’s efficiency.

Water fouling deposits were cited as a major problem at many reactors, especially with condenser tubes where seawater or high-chloride brackish water was the coolant. Pitting corrosion, tube sheet crevice corrosion and galvanic corrosion put the tubes at risk for leakage. Plugging, mud, or detritus accumulating in condenser tubes reduce a power plant’s efficiency.

Utilities use cleaning systems with small, abrasive sponge-like balls to keep the tubes clean and test for tube defectives with probing devices. Tube thinning and corrosion create the opportunity for tube leakage. This can not be tolerated because chemicals such as sodium and chlorides find their way into the reactor vessel or steam generator.

Upgrading the steam condenser tubing to stainless steel also plays a vital role in the ‘power uprate’ program utilities have used to increase generating capacity for existing reactors as we recently discussed. The more advanced uprate program could add up to 20-percent capacity to existing U.S. nuclear reactors.

Diff

nductivity required in steam generation to power nuclear reactor turbines. But copper-alloyed tubes were being replaced too quickly – with an average life of eight years – because of sulphide pitting. Hardest hit were those reactors using polluted seawater to cool their reactors.

Over the past 30 years ago, nuclear utilities slowly began turning to the super austenitic stainless steels as one way to make their nuclear reactors last longer. The addition of molybdenum, initially starting with percentage of less than four percent, helped increase the thermal conductivity lacking in nickel, iron or steel. At nuclear stations which replaced the copper alloys with HPSS condenser tubes, 57 percent rated the thermal performance good and all but one rated it normal. Molybdenum had helped overcome the thermal hurdle.

A large number of the 190 nuclear reactors, which now utilize HPSS condenser tubes, reported an average life in excess of 18 years. The longest stainless steel condenser installation has remained in service more than 26 years, according to a study done several years ago. According to a report published in 2000, more than 100 million feet of super-alloy stainless steel tubes have replaced the older, copper-alloy tubing.

Condensers are large heat exchangers used in nuclear power plants. Condensers have thousands of tubes horizontally mounted to condense and recover the steam passing through turbines. Each low-pressure turbine generally has a condenser, which also maintains a vacuum to optimize the turbine’s efficiency.

Water fouling deposits were cited as a major problem at many reactors, especially with condenser tubes where seawater or high-chloride brackish water was the coolant. Pitting corrosion, tube sheet crevice corrosion and galvanic corrosion put the tubes at risk for leakage. Plugging, mud, or detritus accumulating in condenser tubes reduce a power plant’s efficiency.

Utilities use cleaning systems with small, abrasive sponge-like balls to keep the tubes clean and test for tube defectives with probing devices. Tube thinning and corrosion create the opportunity for tube leakage. This can not be tolerated because chemicals such as sodium and chlorides find their way into the reactor vessel or steam generator.

Upgrading the steam condenser tubing to stainless steel also plays a vital role in the ‘power uprate’ program utilities have used to increase generating capacity for existing reactors as we recently discussed. The more advanced uprate program could add up to 20-percent capacity to existing U.S. nuclear reactors.

Dif

opper alloys with HPSS condenser tubes, 57 percent rated the thermal performance good and all but one rated it normal. Molybdenum had helped overcome the thermal hurdle.

A large number of the 190 nuclear reactors, which now utilize HPSS condenser tubes, reported an average life in excess of 18 years. The longest stainless steel condenser installation has remained in service more than 26 years, according to a study done several years ago. According to a report published in 2000, more than 100 million feet of super-alloy stainless steel tubes have replaced the older, copper-alloy tubing.

Condensers are large heat exchangers used in nuclear power plants. Condensers have thousands of tubes horizontally mounted to condense and recover the steam passing through turbines. Each low-pressure turbine generally has a condenser, which also maintains a vacuum to optimize the turbine’s efficiency.

Water fouling deposits were cited as a major problem at many reactors, especially with condenser tubes where seawater or high-chloride brackish water was the coolant. Pitting corrosion, tube sheet crevice corrosion and galvanic corrosion put the tubes at risk for leakage. Plugging, mud, or detritus accumulating in condenser tubes reduce a power plant’s efficiency.

Utilities use cleaning systems with small, abrasive sponge-like balls to keep the tubes clean and test for tube defectives with probing devices. Tube thinning and corrosion create the opportunity for tube leakage. This can not be tolerated because chemicals such as sodium and chlorides find their way into the reactor vessel or steam generator.

Upgrading the steam condenser tubing to stainless steel also plays a vital role in the ‘power uprate’ program utilities have used to increase generating capacity for existing reactors as we recently discussed. The more advanced uprate program could add up to 20-percent capacity to existing U.S. nuclear reactors.

Dif

ear power plants. Condensers have thousands of tubes horizontally mounted to condense and recover the steam passing through turbines. Each low-pressure turbine generally has a condenser, which also maintains a vacuum to optimize the turbine’s efficiency.

Water fouling deposits were cited as a major problem at many reactors, especially with condenser tubes where seawater or high-chloride brackish water was the coolant. Pitting corrosion, tube sheet crevice corrosion and galvanic corrosion put the tubes at risk for leakage. Plugging, mud, or detritus accumulating in condenser tubes reduce a power plant’s efficiency.

Utilities use cleaning systems with small, abrasive sponge-like balls to keep the tubes clean and test for tube defectives with probing devices. Tube thinning and corrosion create the opportunity for tube leakage. This can not be tolerated because chemicals such as sodium and chlorides find their way into the reactor vessel or steam generator.

Upgrading the steam condenser tubing to stainless steel also plays a vital role in the ‘power uprate’ program utilities have used to increase generating capacity for existing reactors as we recently discussed. The more advanced uprate program could add up to 20-percent capacity to existing U.S. nuclear reactors.

Dif

g systems with small, abrasive sponge-like balls to keep the tubes clean and test for tube defectives with probing devices. Tube thinning and corrosion create the opportunity for tube leakage. This can not be tolerated because chemicals such as sodium and chlorides find their way into the reactor vessel or steam generator.

Upgrading the steam condenser tubing to stainless steel also plays a vital role in the ‘power uprate’ program utilities have used to increase generating capacity for existing reactors as we recently discussed. The more advanced uprate program could add up to 20-percent capacity to existing U.S. nuclear reactors.

Different Molybdenum Alloys

There are several HPSS manufacturers for nuclear reactor condensers. The most prominent in the nuclear sector include Pennsylvania-based ATI Allegheny Ludlum and Finland’s Outokumpu. Each offers austenitic steels with chromium and nickel composition of between 20 and 25 percent for each alloy and a range of 6.2 to 7.5 percent molybdenum.

In a paper presented by Jan Olsson of Avesta Sheffield (before the company was acquired by Outokumpu), he highlighted the results of tests performed on the new super-austenitic stainless steel, 654 SMO®. Metals comprising this brand include 25-percent chromium, 22-percent nickel and 7.5-percent molybdenum. To increase pitting resistance, the manufacturers added up to 0.5-percent nitrogen and three-percent manganese (for make the nitrogen more soluble).

As with all pioneering developments – and remember that R & D breakthroughs have taken place over a two-decade-plus period, manufacturers have re-designed their metallurgical composition to find the most encouraging percentages of nickel, chromium, molybdenum and nitrogen. The earlier stainless steels relied on higher nickel content and lesser percentages of chromium and molybdenum.

At first, conventional austenitic grades, such as 316L, or high chromium-ferritic grades, were utilized. Pitting struck down widespread use of the 316L series and was replaced by higher alloy steels. For example, others, such as the 254 SMO® stainless steel, began aggressively replacing the copper alloy tubes and in some cases the 316L series. The 254 is comprised of 20-percent chromium, 18-percent nickel, 6.2-percent molybdenum and 0.20-percent nitrogen. It has also offered a high level of corrosion resistance at desalination plants without becoming cost-prohibitive.

The most significant breakthrough came after various stainless steels were tested at Scandinavian coastal reactors. In the Avesta paper, the failures of each lesser austenitic grade were checked off. Significant deficiencies included insufficient stress corrosion cracking resistance and resistance to natural seawater. Even titanium tubing was used as an interim measure because it increased total heat transfer by 17 percent, but the metal failed to stand up to high velocity steam and suffered ‘water droplet erosion.’

According to the study, “The only alloy fully resistant to all test conditions was 654 SMO®.” The results at nuclear power plants in Finland and Sweden, along the Baltic Sea, were astonishing! Four important conclusions about this super alloy were reached after the testing.