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Achieving Predictable Valve Performance for Safety Applications

Achieving Predictable Valve Performance for Safety Applications

A focus on having the proper specificati...

Putting Servo Valves Back to Work

Putting Servo Valves Back to Work

Industries as varied as paper production...

Corrosion and Fouling: Is There a Solution?

Corrosion and Fouling: Is There a Solution?

According to a 1998 study released by the ...

Valves with All the Trimmings

Valves with All the Trimmings

The term valve trim has been around for ...

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Industry Headlines

IHS Markit Manufacturing Index Rose in February

Thursday, 22 February 2018  |  Chris Guy

U.S. manufacturers reported a strong upturn in business conditions during February, which continued the positive trend seen at the start of 2018. At 5...

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Valve Positioners Offer Improved Control Valve Performance

Valve Positioners Offer Improved Control Valve Performance

Monday, 19 February 2018  |  David Matherly

From time to time, we are re-posting well-received or particularly valuable articles that have previously run on VALVEMagazine.com so that those who m...

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Industry Headlines

MRC Global Announces Fourth Quarter 2017 Results

17 HOURS AGO

MRC Global’s sales were $903 million for the fourth quarter of 2017, which was 26% higher than the fourth quarter of 2016 and 6% lower than the third quarter of 2017 due to seasonality. As compared to 2016, all sectors increased driven primarily by midstream and upstream.

MRC Global's fourth qu...

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Curtiss-Wright Acquires Dresser-Rand Government Business

1 DAY AGO

Curtiss-Wright has entered into an agreement to acquire the assets that comprise the Dresser-Rand Government Business (Dresser-Rand), a business unit of Siemens Government Technologies, for $212.5 million in cash.

Dresser-Rand designs and manufactures mission-critical, high-speed rotating equipment sol...

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U.S. Refiners Increasingly Turning to Export Markets

20 HOURS AGO

“U.S. gasoline consumption has leveled off as the stimulus provided by low and falling oil prices between 2014 and 2016 has faded, so refiners are increasingly turning to diesel and customers in emerging markets,” Reuters  reports .

“In geographical terms, the fastest growth in co...

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$900M Power Plant Planned for Indiana

20 HOURS AGO

Vectren Energy Delivery of Indiana is proposing to install an additional 50 megawatts (MW) of universal solar and build an 800 to 900-MW natural gas-fired generation facility in addition to other critical investments that will significantly change the way the company generates power for the region .

Th...

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IHS Markit Manufacturing Index Rose in February

-1 DAYS AGO

U.S. manufacturers reported a strong upturn in business conditions during February, which continued the positive trend seen at the start of 2018. At 55.9, up from 55.5 in January, the seasonally adjusted IHS Markit Flash U.S. Manufacturing Purchasing Managers’ Index (PMI) pointed to the fastes...

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Survey Finds Surge in Confidence of Small Business Owners

21 HOURS AGO

CNBC and SurveyMonkey recently announced the results of their quarterly Small Business Survey. According to the findings, 47% percent of small-business owners say overall business conditions are good , up from 44% in the fourth quarter of 2017. Also, 32% of small business owners expect to increase the...

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WCC and LCC Casting in ASME B16.34

materials_q_and_a_graphicQ: Why do WCC and LCC castings have different maximum allowable temperatures in ASME B16.34?

A: This is a very good question and a commonly discussed topic among materials engineers. Unfortunately, the answer isn't black and white-in fact, the "whys" are not very clear at all. What is clear is that the maximum allowable temperature values in B16.34 can be traced back to Section II Part D of the ASME Boiler and Pressure Vessel (B&PV) Code. However, that code contains no background information or notes to explain why those particular temperature limits were assigned. Because of this, much speculation among materials engineers exists- following along these lines:

The standard carbon steel materials (i.e., those not impact-tested for low-temperature applications, such as A216/SA216 WCC) are most commonly heat treated by normalizing, sometimes followed by tempering. Normalized steels are relatively resistant to microstructural changes at elevated temperatures. Short excursions to temperatures below the lower critical temperature (727° C /1340° F) have little or no detrimental effect on the mechanical properties of the steel. Long-term exposure at temperatures exceeding 425° C / 800° F, however, can cause graphitization, in which the carbide phase transforms to graphite causing loss of strength and toughness. WCC is actually allowed at temperatures up to 538° C / 1000° F, but B16.34 notes (as a borrowed reference from the B&PV Code) that "Upon prolonged exposure to temperatures above 455° C / 900° F, the carbide phase of steel may be converted to graphite. This means it may be permissible, but not recommended for prolonged use above 425° C / 800° F."

On the other hand, low-temperature carbon steel materials (i.e., those that are impact-tested for low-temperature applications, such as A352/SA352 LCC) are usually quenched and tempered, because they are generally tougher than normalized microstructures at the same strength level. When exposed to elevated temperatures, quenched and tempered steels are more susceptible than normalized steels to permanent reduction in strength. This is especially true when exposure temperature begins to approach tempering temperature used when the parts were produced. In addition to losing strength, tempered steels also may experience reduced impact toughness after being exposed to long-term elevated temperatures. General belief is that this is the reason for LCC's reduced maximum allowable temperature limit of 345°C / 650°F in B16.34.

Inconsistencies
Here's where inconsistencies start, however, because:

  • A216 / SA216 allows WCC to be supplied in the quenched and tempered condition if the purchaser v invokes Supplementary Requirement S15. A216 / SA216 does not explicitly require any special marking for quenching and tempering. (Interestingly, though, Supplementary Requirement S15 in A703/SA703, the "general requirements" specification referenced by A216 / SA216, stipulates a "QT" mark when the material is quenched and tempered). B16.34 (and the B&PV Code) do not place any special temperature limits on WCC when it is quenched and tempered.
  • In addition, impact tests are also allowed on a WCC casting at -46°C/-50°F to qualify it for low temperature service. This would then be a full-fledged WCC casting qualified for use down to -46°C/-50°F and minus the explicit 345°C/650°F maximum allowable temperature limit for LCC.
  • Furthermore, the B16.34 maximum allowable temperature for A350/SA350 LF2 forgings is 538°C/1000°F (with the same warning note about graphitization -not to use it above 425°C / 800°F). These forgings are also often quenched and tempered so they are essentially the nearest forged equivalent to LCC castings. If the metallurgical instability issues are the reason for the 345°C / 650°F maximum allowable temperature limit on LCC castings then, it would seem that LF2 forgings should also be limited to 345°C / 650°F.

Drawing Conclusions
Based on the above information, the following conclusions might be drawn:

  • If the reduced maximum allowable temperature for impact-qualified materials (such as LCC) are limited based on loss of toughness after long-term exposure to elevated temperatures, it would seem logical that additional, more consistent controls should be placed on all low-temperature materials (including LF2 forgings). These controls would need to extend to grades traditionally not impact tested, but that might be impact tested to qualify them for low temperature applications (such as an impact-tested WCC). In other words, maximum allowable temperature limit should be based on minimum allowable temperature.
  • If the reduced maximum allowable temperature is limited based on loss of strength from reduced elevated-temperature stability of quenched and tempered steels, it would make sense to list maximum allowable temperature limits for carbon steels as a function of both material grade and also heat treat condition. It would also make sense that quenched and tempered materials be marked in this case as well.
  • If both these concerns are driving the reduced maximum allowable temperature limits, then it would seem that the maximum temperature limits of all carbon steels should be based on both the minimum allowable temperature and the heat treat condition. In any event, it's clear that the ASME codes and standards currently contain a number of inconsistencies regarding lower temperature limits in carbon steels.

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