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VMA Technical Event: Engineering Valves in the Extreme

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Industry Headlines

Colorado Seeing Surge in Oil & Gas Investments

Tuesday, 28 March 2017  |  Chris Guy

“Drilling applications and investments by oil and gas companies are surging in Colorado after crude prices partially rebounded from their collap...

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Industry Headlines

Emerson Opens Second Additive Manufacturing Center

1 DAY AGO

With the goal of spurring innovation to address customers’ engineering design challenges and accelerating speed to market for new, rigorously-tested products, Emerson opened an advanced additive manufacturing center at its Singapore campus. This is Emerson’s second location to have additiv...

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GE Oil & Gas Expands with New Sub Saharan Africa Facility

5 DAYS AGO

GE Oil & Gas opened a new facility in Takoradi Port, Ghana, expanding its global footprint and supporting local investment. The facility, which will be the primary service center for deep-water offshore projects in Ghana, has a 1,600 square meter indoor test area with capability for testing thre...

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Colorado Seeing Surge in Oil & Gas Investments

5 HOURS AGO

“Drilling applications and investments by oil and gas companies are surging in Colorado after crude prices partially rebounded from their collapse in recent years, pushing the industry deeper into residential communities largely unaccustomed to drilling,” the Associated Press is reporting .

&...

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U.S. Specialty Chemicals Markets Accelerated in February

1 DAY AGO

The American Chemistry Council (ACC) reported that U.S. specialty chemicals market volumes rose a strong 0.6% in February. This follows an upwardly revised 0.4% gain in January. Volumes have generally been moving up since May. All changes in the data are reported on a three-month moving average (3MMA)...

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Four Out of Ten Jobs Could be Lost to Automation by 2021

5 HOURS AGO

Automation is the new norm across sectors and will affect the bottom of pyramid so much so that four out of every 10 jobs globally would be lost due to this by 2021, experts say. As automation adoption increases, all high transaction and labor intensive jobs will take a hit. According to PeopleStrong...

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U.S. Durable Goods Orders Rose 1.7% in February

1 DAY AGO

New orders for manufactured durable goods in February increased $3.9 billion or 1.7% to $235.4 billion, the U.S. Department of Commerce announced . This increase, up two consecutive months, followed a 2.3% January increase. Excluding transportation, new orders increased 0.4%. Excluding defense, new or...

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Which Valve for Nitric Acid Service?

materials_q_and_a_graphicQ: I requested CF8 valves but the supplier is offering CF8M valves at less cost. However, I am not sure this alternative is a good choice for my nitric acid service. Are my concerns warranted?

 

A: Suppliers of cast valves may offer certain higher alloys at the same or less cost for a couple of reasons. Before getting into your concern about nitric acid, let’s address the issue about the cost of certain cast alloys. First, we’ll look at the cast versions of 304 and 316 stainless steel, known as CF8 and CF8M respectively. The compositional makeup of these two alloys are similar: chromium and nickel contents. However, CF8M contains 2% to 3% molybdenum that CF8 does not have, so we might expect CF8M to cost more. That is not usually the case. This is because alloy content is only one variable in the cost of an alloy; an equally important one is volume. While wrought producers make a significant quantity of 304 SS at less cost than 316 SS, foundries traditionally have standardized cast 316 (CF8M). The reason is that CF8M has much broader applications than CF8, so foundries produce a much greater volume of CF8M valves and benefit from the economies of scale. Thus, CF8M valves are usually less expensive than CF8 valves.


OTHER PRICING ISSUES

There are a few other reasons some cast alloys are priced at levels that seem contradictory, including whether an alloy is “foundry friendly.” In other words, can the alloy be produced without any consistent problems as a casting? For example, CA15 (410 SS) should be expected to cost less than its newer version, CA6NM. However, when you take into account castability and weldability issues, most foundries would prefer to make CA6NM rather than CA15. Because of this, these foundries will either price CA6NM less or the same as CA15, and the customer benefits by getting an alloy that has better ductility, impact toughness and corrosion resistance than CA15.

A foundry unfriendly alloy is grade 12 titanium. Grade 12 contains a small amount of nickel and molybdenum and was developed as a less expensive alternative to the palladium-stabilized titanium grades while having almost the same corrosion resistance. While this may not be a difficult alloy for wrought producers to make, the alloy is more difficult to cast than the palladium grades. In addition, weld repairs on grade 12 must be stress relieved, which adds cost to the foundry. As a result, some reactive alloy foundries will price grade 12 titanium the same as the more corrosion-resistant palladium grades. In this case, there may be no cost benefit in specifying grade 12 cast titanium valves.

NITRIC ACID APPLICATION

Let’s return to the concern about using CF8M in nitric acid services. 304 SS is certainly a good choice for most nitric acid applications, and it is used extensively as wrought piping, vessels, tanks, etc., that are handling nitric acid. As a result, when it comes to valves, it is only natural to select CF8 thinking it will be less expensive than CF8M. For reasons discussed previously, this may not be true. Therefore, the remaining question is whether CF8M is suitable for nitric acid service. In my experience, it is. I have reviewed considerable corrosion data and conducted numerous corrosion tests for CF8 and CF8M and found little difference in corrosion rates between the two alloys in nitric acid applications. The difference usually is only a couple of mils per year, sometimes in favor of CF8, but other times in favor of CF8M (Figure 1).

vmsum11_materials_fig1Figure 1.
THE GRADE LEVEL

Another issue people struggle with concerning nitric acid is whether they should use the low-carbon grades: 304L, 316L or the cast equivalents CF3 and CF3M. The concern is that nitric acid is a strong oxidizing acid that can cause intergranular corrosion—one way to minimize the susceptibility to intergranular corrosion is to use the low-carbon grades. The use of these grades makes sense for wrought components such as piping, vessels and tanks that are welded in the field and cannot easily be post-weld heat treated. However, it is practical and sometimes required by ASTM specifications such as A744 to post-weld heat treated castings. Therefore, if the higher carbon CF8 and CF8M alloys are post-weld, heat treated, they can be used and will not experience intergranular corrosion in a nitric acid service.

Because of all of this, the choice between these CF8 and CF8M for nitric acid service should be based on price and availability.


THOMAS SPENCE is director of materials engineering for Flowserve Corp. (www.flowserve.com), Dayton, OH. Reach him at This email address is being protected from spambots. You need JavaScript enabled to view it..

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