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Valve Selection in Pulp and Paper Operations

Valve Selection in Pulp and Paper Operations

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VMA Technical Event: Engineering Valves in the Extreme

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Industry Headlines

Kansas City Fed Shows Manufacturing At 6-Year High

Friday, 24 March 2017  |  Chris Guy

Tenth District manufacturing activity strengthened further in March, and many indexes of expectations for future activity were at or near record highs...

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Industry Headlines

GE Oil & Gas Expands with New Sub Saharan Africa Facility

2 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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Metso Launches Digital Program to Accelerate Growth

3 DAYS AGO

Metso has set up a Digital Program to accelerate the company’s digital capabilities, which are required to succeed in the future of minerals processing and flow control. Metso's ambition is to become one of the digital leaders in the industries it serves. This means for example turning custome...

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Shell Looking to Lower Cost of Offshore Projects

2 DAYS AGO

“With oil prices hovering around $50 a barrel or less, and a rising amount of renewable energy chipping away at market share, Shell is going lean on its deepwater projects to make sure it can eke out a profit from all of its operations,” writes ChemInfo .

For example, Shell is attempting to ...

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Report Says PA Can Support Four More Ethane Crackers

2 DAYS AGO

A new report from IHS Markit, commissioned by the state of Pennsylvania, forecasts $2.7 to 3.7 billion in investments in natural gas liquid (NGL) assets as well as the opportunity to attract additional cracker plants, and petrochemical and plastics manufacturing. IHS Markit believes the Marcellus an...

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Kansas City Fed Shows Manufacturing At 6-Year High

1 DAY AGO

Tenth District manufacturing activity strengthened further in March, and many indexes of expectations for future activity were at or near record highs. Most price indexes increased moderately. The month-over-month composite index was 20 in March , its highest reading since March 2011, up from 14 in Fe...

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Consumer Sentiment Reaches Highest Level Since 2000

5 DAYS AGO

The overall level of consumer sentiment remained quite favorable in early March due to renewed strength in current economic conditions as well as the extraordinary influence of partisanship on economic prospects. The current economic conditions component reached its highest level since 2000, largely...

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Austenitic Stainless Steels

materials_q_and_a_graphicQ: Do austenitic stainless steels require impact testing when used in low-temperature applications?

 

A: Austenitic materials are generally recognized for their lack of ductile-to-brittle transition behavior. In other words, they do not generally display a reduction in impact energy as the test temperature is reduced. By contrast, ferritic and martensitic materials-such as the carbon steels, alloy steels, and 400-series stainless steels-exhibit reduced toughness as test temperature is reduced.

 

Wrought vs. Cast
The wrought forms of the austenitic stainless steels used for pressure-retaining components (forgings, plate, pipe, etc.) are typically supplied in the solution-annealed condition with a fully austenitic structure. These materials suffer essentially no reduction in toughness even at cryogenic temperatures. For example, notched Charpy specimens of Types 304 and 316 stainless steel in the solution-annealed condition will routinely stop the hammer on smaller Charpy machines. On larger machines, the impact will bend the specimens far enough that they pass between the specimen supports and are thrown from the tester, but they will not crack or break.

Cast versions of the austenitic stainless steels are slightly different. The cast versions have slightly modified chemistries that are balanced to produce a microstructure containing some ferrite. This is done to prevent hot cracking during solidification and cooling in the mold. As mentioned above, the ferrite phase will undergo a ductileto-brittle transition at low temperatures. The issue is whether the impact toughness is significantly reduced by the presence of ferrite in the amounts commonly encountered in these cast alloys.

The fifth edition of the Steel Castings Handbook (published by the Steel Founders' Society of America) includes a graph of Charpy V-notch toughness vs. temperature for CF8 (cast Type 304). The graph indicates the impact energy gradually declines from 125-215 ft-lbs [170-292 J] at ambient temperature down to 37-70 ft-lbs [50-95 J] at -325° F [-198° C]. The gradual decline indicates there is no abrupt ductile- to-brittle transition temperature, and the relatively high impact energy (when contrasted with the 15/12 ft-lbs [20/16 J] minimum requirement for ASTM A352 and ASME SA352 LCC) indicates the material is still very tough even at liquid nitrogen temperatures.

A major North American supplier of valve castings provided data on 69 heats of various CF-series castings that were impact tested at -320° F [-198° C], the temperature of liquid nitrogen. All heats exceeded 20 ft-lb [27 J] except one, and that heat, which averaged 18 ft-lbs [24 J] still exceeded the 15/12 ft-lbs [20/16 J] minimum requirement that applies to LCC.

ASTM and ASME vs. EN and PED
This would seem to indicate that impact testing of the CF-series castings is not necessary. The ASTM A351 and ASME SA351 specifications that cover these materials do not require impact testing, and in fact do not list impact testing among the supplementary requirements that are ordinarily considered suitable for use with these materials.

On the other hand, the European standard EN 10213 Part 4, which includes several grades that are similar to the CF-series cast alloys, requires impact testing at ambient temperature, with acceptance criteria ranging from 30-60 ft-lbs [40-80 J], depending on the particular alloy. When the steels are to be used at low temperatures, there are specific impact test temperatures and acceptance criteria listed for several of the alloys.

The various codes and regulations also handle this issue quite differently. For example, the ASME B31.3 Process Piping Code specifies minimum allow-able temperatures for materials in Table A-1. The minimum allowable temperature for the common austenitic materials (S30400, S31600, CF8, CF8M, etc.) ranges from -425° F [-254° C] to -325° F [-198° C], depending on the specific material grade and form. Impact testing is not required, although impact-qualified weld filler materials are required in certain cases when the materials are welded.

Yet the European Pressure Equipment Directive (PED) requires steel materials to exhibit a minimum Charpy V-notch impact energy of 20 ft-lbs [27 J] at 68° F [20° C] or at the minimum design operating temperature, whichever is lower. However, this requirement is waived for a material when there is no doubt that the essential safety requirement for toughness will be fulfilled even if the impact tests are not performed (see Guideline 7/17).

This stipulation would seem to excuse the wrought austenitic stainless steels from testing even at very low temperatures, since they do not exhibit ductile-to-brittle transition behavior. However, because of the presence of ferrite in castings, and the effect of that ferrite on the low-temperature impact properties, the acceptability of cast austenitic stainless steels for PED applications without impact testing is questionable.

It is important to note, however, that Guideline 7/17 includes this statement: "Every harmonized European steel standard has specifications for impact properties." This is true even for the wrought austenitic stainless-steel grades.

No Simple Anwser
In summary, there is no simple answer to this question. Whether impact tests are required for austenitic stainless steels for low-temperature applications depends primarily on the point of view of the customer. For the most part, the North American specifications and codes do not require impact testing of these materials for temperatures down to at least -325° F [-198° C], even in the cast form. The European specifications and codes require impact testing of all forms even when used at ambient temperature. The situation is not likely to change in the foreseeable future.

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