09282016Wed
Last updateTue, 27 Sep 2016 9pm

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Wolseley Reports 2016 Full Year Results

11 HOURS AGO

Wolseley plc delivered an improvement in overall results for the fiscal year ending July 31, 2016, up 8.5% from last year. Revenue of $18.7 billion was 4.2% ahead at constant exchange rates and 2.4% ahead on a like-for-like basis. Price deflation, particularly in the U.S., reduced revenue by 1.5%. Imp...

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ValvTechnologies Joins MSS of the Valve and Fittings Industry Committee

16 HOURS AGO

ValvTechnologies, Inc. has been unanimously approved for membership in the Manufacturers Standardization Society (MSS) of the Valve and Fittings Industry Committee. Representing ValvTechnologies is Tony Majka, director of engineering.

The MSS is a non-profit technical association organized for develo...

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Alaska, ConocoPhillips Forming LNG Joint Venture

1 DAY AGO

The State of Alaska, through the Alaska Gasline Development Corporation (AGDC), and ConocoPhillips Alaska Inc. have executed a Memorandum of Understanding regarding negotiations to form a joint venture (JV) that could facilitate marketing LNG from the Alaska LNG project to global LNG markets and acqui...

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Many Houston Chemical Facilities Could Be Operating Illegally

1 DAY AGO

“Firefighters once routinely visited buildings in their districts to plan for emergencies — including ferreting out hazmat sites — but those visits stopped in April 2014. The department had started entering old plans into a new, sophisticated database and didn't want to create a ba...

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U.S. Consumer Confidence Surges to Nine-Year High

16 HOURS AGO

The Conference Board Consumer Confidence Index, which had increased in August, improved further in September. The Index now stands at 104.1, up from 101.8 in August. The 104.1 figure is the highest since August 2007.

“Consumer confidence increased in September for a second consecutive month and i...

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Texas Manufacturing Strengthened in September

16 HOURS AGO

Texas factory activity increased markedly in September, according to business executives responding to the Texas Manufacturing Outlook Survey . The production index, a key measure of state manufacturing conditions, rose 12 points to 16.7, suggesting output picked up at a notably faster pace this month...

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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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