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Basics of Elastomeric Seal Design

Basics of Elastomeric Seal Design

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Controlling Our Water Systems, Part II

Controlling Our Water Systems, Part II

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Controlling Our Water Systems

Controlling Our Water Systems

Actuators and controls are a critical pr...

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Pentair Reports Second Quarter 2016 Results

1 DAY AGO

Pentair plc announced second quarter 2016 sales of $1.7B. Sales were up 4% compared to sales for the same period last year. Excluding the unfavorable impact of currency translation and the positive contribution from acquisitions, core sales declined 3% in the second quarter . Second quarter 2016 earni...

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ValvTechnologies Names Bryant Holt Industry Director, Fossil Power

2 DAYS AGO
ValvTechnologies Names Bryant Holt Industry Director, Fossil Power

ValvTechnologies, Inc. has appointed Bryant Holt as industry director for the company’s fossil power division. Holt will succeed George Stover, who has served in this role since 2014.

Based in Houston, Holt will have global management responsibility for ValvTechnologies’ fossil power group ...

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ExxonMobil Expanding Beaumont, TX Facility

1 DAY AGO

ExxonMobil has plans to increase production of ultra-low sulfur fuels at its Beaumont, TX refinery by approximately 40,000 barrels per day, representing an investment of approximately $450 million.

Construction is scheduled during the second half of 2016 to install a selective cat naphtha hydrofining u...

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LNG’s Surge from Decade-Low Seen Fizzling as Supply Ramps Up

2 DAYS AGO

“LNG’s surge is running out of gas. Liquefied natural gas in Asia, which was in such over-supply that prices in Japan fell to a decade-low in April, has risen by almost half in the past three months as production outages stifled supply, demand rose in places like China and India and a co...

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Second Quarter GDP Grew Only 1.2% in Second Quarter

6 HOURS AGO

Real GDP in the U.S. increased at an annual rate of 1.2% in the second quarter of 2016, according to the advance estimate released by the U.S. Department of Commerce. In the first quarter, real GDP increased 0.8%.

The increase in real GDP in the second quarter reflected positive contributions from cons...

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U.S. Durable Goods Orders Down 4% in June

2 DAYS AGO

New orders for manufactured durable goods in June decreased $9.3 billion or 4.0% to $219.8 billion, the U.S. Department of Commerce announced. This decrease , down two consecutive months, followed a 2.8% May decrease. Excluding transportation, new orders decreased 0.5%. Excluding defense, new orders d...

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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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