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Last updateFri, 27 May 2016 2pm

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Industry and Regulatory Changes in Offshore Operations

Industry and Regulatory Changes in Offshore Operations

On May 13, 2016, the offshore oil and ga...

Strategies for Successful SIS Valve Diagnostic Implementation

Strategies for Successful SIS Valve Diagnostic Implementation

End users and contractors alike strive t...

Stop Check Valves

Stop Check Valves

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ValvTechnologies Names Garcia, Mermelstein to New Positions

3 DAYS AGO
ValvTechnologies Names Garcia, Mermelstein to New Positions

ValvTechnologies, Inc. has named David Garcia director of manufacturing and Steve Mermelstein as regional director, Americas and director, channel management.

Previously, West Point graduate Garcia served as director of operations for Merla Wellhead Solutions and held plant manager positions at Hallib...

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Emerson Automating UK Waste-to-Energy Plant

3 DAYS AGO

Emerson will provide control systems and project services for a new waste-to-energy power plant near Knaresborough Allerton, North Yorkshire, UK. Construction is expected to be completed in 2017, with the plant fully operational in 2018.

The plant , which will also incorporate biogas and recycling faci...

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U.S. Still Top Producer of Petroleum, Natural Gas Hydrocarbons

2 DAYS AGO

The U.S. remained the world's top producer of petroleum and natural gas hydrocarbons in 2015, according to U.S. Energy Information Administration estimates . U.S. petroleum and natural gas production first surpassed Russia in 2012, and the U.S. has been the world's top producer of natural gas since 20...

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Why $50/Barrel Oil Means Stability to U.S. Producers

2 DAYS AGO

The rise to $50-per-barrel oil means a return to stability, particularly for domestic shale producers, according to Dan K. Eberhart, CEO, Canary, LLC. At this level , companies that saw the value of their product drop more than 75% in less than two years might have the confidence to resume drilling ac...

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Survey: Manufacturing Execs Investing in Advanced Tech

2 DAYS AGO

 A convergence of disruptive factors such as new technologies, increasing competition, and pricing pressures, is forcing manufacturers to increase investment in new products and services as they seek to innovate manufacturing capabilities, according to the 2016 KPMG Global Manufacturing Outlook ...

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Durable Goods Orders Surge 3.4%, But Demand Soft

2 DAYS AGO

New orders for manufactured durable goods in April increased $7.7 billion or 3.4% to $235.9 billion, the U.S. Census Bureau announced today. This increase, up three of the last four months, followed a 1.9% March increase. Excluding transportation, new orders increased 0.4%. Excluding defense, new or...

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Cobalt-base Alloy 6

materials_q_and_a_graphicQ: Is there a problem using cobalt-base Alloy 6 material in amine applications in refineries and gas treatment plants?

A: This is a very good question, and the answer may be somewhat surprising to many people.

The Materials Q&A column in the Winter 2006 issue of Valve Magazine covered erosion-corrosion issues that can occur when cobalt-base Alloy 6 is used for boiler feedwater service in power plants. To review, boiler feedwater is often treated with amine compounds to deoxygenate the water, which reduces the corrosion rates in the steel piping system. It has been theorized (but not proven) that the presence of the amine compounds somehow prevents the reformation of the oxide passive layer on the Alloy 6 after it has been removed by high-velocity flow impingement. What is not understood is why this only occurs in cobalt alloys and not in other materials (such as austenitic stainless steels) that also rely on an oxide passive layer for corrosion protection.

In refineries, amine compounds are used to absorb unwanted dissolved gases—primarily hydrogen sulfide (H2S)—from liquid hydrocarbons. In natural gas treatment plants, the amine compounds are used to absorb H2S and carbon dioxide (CO2). This process is usually called “sweetening.” The most commonly-used compounds in these applications are the alkanolamines—monoethanolamine (MEA), diethanolamine (DEA) and methyldiethanolamine (MDEA).

The gaseous or liquid hydrocarbon is passed up through an absorber, and the amine fluid is passed in a counterflow direction (i.e., down) through the absorber. The unwanted H2S (and CO2 in the case of natural gas) are absorbed by the amine solution, which results in what is called “rich amine.”

In common systems, the rich amine exits the bottom of the absorber and passes through a rich amine letdown valve, where the pressure drop causes the gases to come out of solution.

Commonly, an amine regenerator valve is present that eventually takes a second pressure drop going into the regenerator. Some outgassing also occurs at this valve, but not to the same extent as is present in the rich amine letdown valve.

The regenerator produces what is called “lean” amine solution, which is then recirculated to the absorber.

Valves controlling the lean amine solution are not susceptible to sulfide stress cracking, and not especially susceptible to corrosion (because no H2S or CO2 is present). However, they do tend to be susceptible to cavitation because of the large pressure drops. These valves are usually supplied with anti-cavitation trim in standard hardened stainless-steel materials.

Valves controlling the rich amine are susceptible to both corrosion and sulfide stress cracking because of the H2S (and CO2 in gas treatment) and are susceptible to erosion damage because of the two-phase flow caused by the outgassing. Therefore, it would be favorable to be able to use a trim material in these valves that is known to be resistant to corrosion and sulfide stress cracking and resistant to erosion by the two-phase flow. Alloy 6 is famous for its resistance to various types of mechanical damage, including cavitation damage, flashing damage (which is similar to the two-phase gas-liquid erosion mechanism encountered here) and galling. It’s also commonly used in applications where sulfide stress cracking is a concern. The big question is, how well does Alloy 6 hold up against corrosion, given the fact that there are amines present in the fluid?

One might theorize that the Alloy 6 would suffer the same erosion-corrosion damage in the rich amine solution as it does in boiler feedwater applications. After all, the amines would scavenge oxygen from the water in the amine solution just as they do in boiler feedwater applications.

Deoxygenation does actually occur. In fact, the theory is this may be the reason for the successful use of 316 stainless steel in gas sweetening systems where temperatures and chloride levels would seem elevated enough to cause chloride stress corrosion cracking (SCC). It is known that as dissolved oxygen decreases, the tendency to suffer chloride SCC decreases. Elimination of dissolved oxygen may be the reason that SCC does not occur.

Despite the fact that theory would indicate a danger of erosion-corrosion for Alloy 6 in these applications, experience has indicated that this material actually works very well. There are literally thousands of control valves installed in rich amine letdown service and amine regenerator service that use Alloy 6 trim components. These valves include Alloy 6 in all the various product forms—solid cast components (UNS R30006), solid wrought components (UNS R30016) and hardface overlays (AWS CoCr-A), and they all work well in practice.

In other words, there is no reason to restrict the use of Alloy 6 trim materials in amine applications in refining and gas treatment systems. Save those restrictions for boiler feedwater applications.


Don Bush is principal materials engineer, Advanced Technology Group, Fisher Division, Emerson Process Management.

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