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Industry Headlines

Manufacturers Expecting Increased Revenues, Employment Growth In 2017

Friday, 09 December 2016  |  Chris Guy

Economic growth in the U.S. will continue in 2017, say the nation’s purchasing and supply management executives in their December 2016 Semiannua...

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Industry Headlines

Siemens Industry Acquiring Mentor Graphics for $4.5 Billion

3 DAYS AGO

Siemens and Mentor Graphics have entered into a merger agreement under which Siemens will acquire Mentor for $37.25 per share in cash, which represents an enterprise value of $4.5 billion. Mentor will then be consolidated into Siemens Industry, according to the Atlanta Business Journal .

Mentor Graphics ...

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GE Oil & Gas Signs Agreement with TAG GmbH

3 DAYS AGO

GE Oil & Gas has signed an agreement with TAG (Trans Austria Gasleitung) GmbH, a pipeline operator with stations across Austria, to install its new Tuning Maintenance Software (TUMAS) across TAG’s fleet of 16 PGT25 gas turbines. This is the first time this solution has been rolled out across...

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‘Buy America’ Debate Holds Up Water Infrastructure Bill

2 DAYS AGO

A debate in Congress is taking place over whether to restore a ‘Buy America’ provision in the Water Resources Development Act (WRDA) before a final version is voted on. The ‘Buy America’ rule already passed in the Senate version of the bill. It was then pulled from the compromi...

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New Pipeline Safety Rule Expands Excess Flow Valve Requirements Again

4 DAYS AGO

In October, 2016, The Pipeline and Hazardous Materials Safety Administration (PHMSA) announced a final rule that expands safety requirements for excess flow valves (EFVs) to multi-residential and commercial applications. That version of the rule covered the installation of EFVs in new or replaced se...

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Manufacturers Expecting Increased Revenues, Employment Growth In 2017

1 DAY AGO

Economic growth in the U.S. will continue in 2017, say the nation’s purchasing and supply management executives in their December 2016 Semiannual Economic Forecast. Expectations are for a continuation of the economic recovery that began in mid-2009, as indicated in the monthly ISM Report on Bu...

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Poll: U.S. Economy to Grow 2.2% in 2017

3 DAYS AGO

National Association for Business Economics’ (NABE) December 2016 Outlook Survey forecasts 2.2% growth in real GDP for 2017. The annualized growth rate forecasted for 2017 inched downward to 2.2% in the current survey from 2.3% in September. Both projections illustrate the panel’s expectat...

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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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