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Offshore Production Nearly 30% of Global Crude Oil Output

Wednesday, 26 October 2016  |  Chris Guy

Global offshore oil production (including lease condensate and hydrocarbon gas liquids) in 2015 was at the highest level since 2010, and accounted for...



Industry Headlines

Honeywell and Flowserve Collaborate on IIoT Solutions


Honeywell and Flowserve will collaborate to provide Industrial Internet of Things (IIoT) for industrial customers. The collaboration will be part of the Honeywell INspire program, Honeywell's joint customer development program for its IIoT ecosystem.

Honeywell and Flowserve have a long history of colla...


Train Named Executive President of Emerson Automation Solutions


Emerson recently named new senior leadership appointments to its Office of the Chief Executive who now report directly to chairman and CEO David N. Farr, and help develop and guide the company’s global strategies.

Michael H. Train’s new title is executive president of Emerson Automation Sol...


Offshore Production Nearly 30% of Global Crude Oil Output


Global offshore oil production (including lease condensate and hydrocarbon gas liquids) in 2015 was at the highest level since 2010, and accounted for nearly 30% of total global oil production. Offshore oil production increased in both 2014 and 2015, reversing consecutive annual declines from 2010 t...


New 2017 Construction Starts Increasing 5% to $713 Billion


The 2017 Dodge Construction Outlook predicts that total U.S. construction starts for 2017 will advance 5% to $713 billion, following gains of 11% in 2015 and an estimated 1% in 2016.

Manufacturing plant construction will increase 6%, beginning to recover after steep declines in 2015 and 2016 that refle...


Richmond Fed: Manufacturing Rises But Remains Sluggish


Manufacturing activity fifth district (MD, DC, VA, WV, NC, SC) remained sluggish in October, according to the most recent survey by the Federal Reserve Bank of Richmond. New orders and backlogs decreased this month, while shipments flattened. Hiring activity strengthened mildly across firms and wage i...


Consumer Confidence Retreated in October


The Conference Board Consumer Confidence Index, which had increased in September, declined in October. The index now stands at 98.6, down from 103.5 in September. The present situation index decreased from 127.9 to 120.6, while the expectations index declined from 87.2 last month to 83.9.



Cobalt-based Alloy 6 Materials and Boiler Feedwater Service

materials_q_and_a_graphicQ: I’ve heard that cobalt-base Alloy 6 materials should not be used in boiler feedwater service. Is this true?

A: Cobalt-chromium Alloy 6 is a very popular material for hard valve trim in applications requiring resistance to sliding wear, erosion and/or cavitation. It’s even successfully used in applications that are somewhat corrosive. However, in some areas of boiler feedwater applications where it would seem Alloy 6 should perform well, problems have been encountered. Here are some theories and facts about the problems:

Alloy 6 is available in cast, wrought and weld overlay forms. The cast material designation is UNS R30006; wrought material is designated UNS R30016, but is commonly called Alloy 6B; the generic AWS designation for hardsurfacing material is CoCr-A (specific designations are ECoCr-A for SMAW electrodes and ERCoCr-A for bare electrodes).

Alloy 6 is a cobalt-chromium-tungsten alloy with approximately 1% carbon. The material consists of a soft, solid solution matrix of cobalt-chromium tungsten surrounding a small percentage of hard, brittle chromium carbides.

Although the carbide phase provides the high hardness (approximately 40 HRC), research has shown that the cobalt-chromium-tungsten matrix is responsible for the alloy’s excellent wear and cavitation resistance. Alloy 6 undergoes a phase transformation (i.e., a change in crystal structure) when highly stressed, such as in a wear or cavitation situation. This phase transformation absorbs some energy that would otherwise cause damage, in effect, reducing the overall level of damage compared with a material that does not exhibit this “shock absorption” property.

Like most corrosion-resistant alloys containing chromium as an alloying element, Alloy 6 achieves corrosion resistance from the formation of a stable chromium oxide passive layer. This passive layer protects the underlying material from reacting with the environment. Certain chemicals can weaken the passive layer, reducing its ability to protect the material from corrosion.

Performance problems with Alloy 6 have been experienced in boiler feedwater applications where the water is treated with hydrazine or some other amine derivative. The problems occur exclusively in regions where the flow velocity is high, indicating that the failure mode is actually erosion-corrosion. Two possible explanations for this phenomenon are that:

1) The amine compounds weaken the oxide passive layer so that it erodes easily. The passive layer is repeatedly eroded away and rebuilt, resulting in accelerated corrosion.

2) The amines prevent the oxide passive layer from reforming after it has eroded initially, thus leaving the alloy unprotected from corrosion. Further erosion-corrosion then occurs at accelerated rates.

Other possible mechanisms for this type of failure may also exist, but the point remains that the alloy is attacked at higher rates than would be expected in an equivalent water application without the presence of the amine compounds.

Studies of returned parts have demonstrated that these attacks definitely correlate to the presence of Alloy 6. The photographs in Figures 1 through 4 were obtained during evaluation of a valve plug with Alloy 6 seat and guide surfaces that suffered erosion- corrosion damage in boiler feedwater. It’s very clear that the damage occurred exclusively in the CoCr-A material, and that the adjacent S31600 material is relatively unaffected, even though it is much softer.

Many failures have occurred in feedwater regulating valves, too. Failures have been reported in special- and standard-trim valves operating at temperatures as low as 300° F (149° C) and pressure drops as low as 100 psi (7 bar). Similar failures have been experienced in tungsten carbide trim in amine-treated feedwater and in ammonia applications when a cobalt binder phase is used.

No amine content, temperature or velocity limits have been established for safe use of Alloy 6 materials in feedwater. Common practice is to avoid the use of cobalt-containing alloys in feedwater service unless the feedwater is known to be compatible with cobalt alloys.

Common alternatives to Alloy 6 include hardened stainless steels such as S41600 (Type 416 SST), S41000 (Type 410 SST), S42000 (Type 420 SST), S44004 (Type 440C SST), or S17400 (17-4 PH SST). In some severely erosive applications, nickel base or iron-base hard-surfacing materials have been used.

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