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Last updateTue, 28 Jun 2016 8pm

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Fugitive Emissions—Issues and Opportunities

Fugitive Emissions—Issues and Opportunities

Fugitive emissions, ppm, consent decrees...

Problem-Driven Innovation

Problem-Driven Innovation

Developing Alternative Technology to Imp...

Valve Repair Takes Center Stage in Houston

Valve Repair Takes Center Stage in Houston

Attendees gathered June 2-3 in Houston t...

What Internal Best Practices Can Do for Valve Selection

What Internal Best Practices Can Do for Valve Selection

As time goes by, technology moves forwar...

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Industry Headlines

Oil Sands Production Forecast to Grow by Nearly 1M bpd

Tuesday, 28 June 2016  |  Chris Guy

IHS, in its outlook for Canadian oil sands production through 2025, expects continued growth through the period. IHS anticipates a new phase driven pr...

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Industry Headlines

MSS Publishes Revised Standard for High Pressure Knife Gate Valves

14 HOURS AGO

The Manufacturers Standardization Society (MSS) announces that recently revised Standard Practice, SP-135-2016, High Pressure Knife Gate Valves, has been approved by the American National Standards Institute (ANSI) as an American National Standard (ANS).

The first edition of MSS SP-135 was published in...

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Admiral Valve Joins VMA

14 HOURS AGO
Admiral Valve Joins VMA

This week the Valve Manufacturers Association (VMA) welcomed Admiral Valve LLC dba CPV Manufacturing , our sixth new member in 2016.

Admiral Valve, LLC designs and manufactures high-performance filtration systems for marine and aerospace use from their 30,000 square foot facility in the Philadelphia su...

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Oil Sands Production Forecast to Grow by Nearly 1M bpd

9 HOURS AGO

IHS, in its outlook for Canadian oil sands production through 2025, expects continued growth through the period. IHS anticipates a new phase driven primarily by the expansion of existing facilities with more attractive economics.

Oil sands production is forecast to grow by nearly one million barrels pe...

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Construction of Chemical Processing Facilities Begins in Louisiana

10 HOURS AGO

This month, LACC LLC, the joint-venture company formed by Axiall Corporation and Lotte Chemical Corporation, held a groundbreaking ceremony at its Calcasieu Parish, LA construction site. This follows a Dec. 17, 2015 announcement that the boards of Lotte and Axiall reached final investment decisions ...

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Consumer Confidence Climbs to 8-Month High

14 HOURS AGO

The Conference Board Consumer Confidence Index, which had decreased in May, improved in June. The Index now stands at 98.0 , up from 92.4 in May. Those stating business conditions are “good” increased slightly from 26.1% to 26.9%, while those saying business conditions are “bad&rdquo...

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How Will Brexit Affect the Manufacturing Industry?

1 DAY AGO

The day after the Brexit decision, National Association of Manufacturers (NAM) chief economist Chad Moutray addressed the UK vote to leave the EU and its effect on the manufacturing industry as well as the element of uncertainty it adds to the global marketplace.

According to Moutray, “If you are...

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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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