07282016Thu
Last updateThu, 28 Jul 2016 6pm

i

Basics of Elastomeric Seal Design

Basics of Elastomeric Seal Design

Engineers need critical design informati...

Wastewater Treatment

Wastewater Treatment

Society’s desire for a clean envir...

Controlling Our Water Systems, Part II

Controlling Our Water Systems, Part II

To better understand the actuators and c...

Controlling Our Water Systems

Controlling Our Water Systems

Actuators and controls are a critical pr...

The Weekly Report

New Products

  • ja-news-2
  • ja-news-3

Industry Headlines

Pentair Reports Second Quarter 2016 Results

Thursday, 28 July 2016  |  Chris Guy

Pentair plc announced second quarter 2016 sales of $1.7B. Sales were up 4% compared to sales for the same period last year. Excluding the unfavorable ...

Readmore

Loading...
Advertisement
i

Industry Headlines

Pentair Reports Second Quarter 2016 Results

2 HOURS AGO

Pentair plc announced second quarter 2016 sales of $1.7B. Sales were up 4% compared to sales for the same period last year. Excluding the unfavorable impact of currency translation and the positive contribution from acquisitions, core sales declined 3% in the second quarter . Second quarter 2016 earni...

Readmore

ValvTechnologies Names Bryant Holt Industry Director, Fossil Power

1 DAY AGO
ValvTechnologies Names Bryant Holt Industry Director, Fossil Power

ValvTechnologies, Inc. has appointed Bryant Holt as industry director for the company’s fossil power division. Holt will succeed George Stover, who has served in this role since 2014.

Based in Houston, Holt will have global management responsibility for ValvTechnologies’ fossil power group ...

Readmore

ExxonMobil Expanding Beaumont, TX Facility

6 HOURS AGO

ExxonMobil has plans to increase production of ultra-low sulfur fuels at its Beaumont, TX refinery by approximately 40,000 barrels per day, representing an investment of approximately $450 million.

Construction is scheduled during the second half of 2016 to install a selective cat naphtha hydrofining u...

Readmore

LNG’s Surge from Decade-Low Seen Fizzling as Supply Ramps Up

1 DAY AGO

“LNG’s surge is running out of gas. Liquefied natural gas in Asia, which was in such over-supply that prices in Japan fell to a decade-low in April, has risen by almost half in the past three months as production outages stifled supply, demand rose in places like China and India and a co...

Readmore

U.S. Durable Goods Orders Down 4% in June

1 DAY AGO

New orders for manufactured durable goods in June decreased $9.3 billion or 4.0% to $219.8 billion, the U.S. Department of Commerce announced. This decrease , down two consecutive months, followed a 2.8% May decrease. Excluding transportation, new orders decreased 0.5%. Excluding defense, new orders d...

Readmore

Sharpest Rise in U.S. Manufacturing Production Since November

3 DAYS AGO

July data signaled a further rebound in business conditions across the U.S. manufacturing sector, led by a robust expansion of incoming new work and the fastest upturn in production volumes for eight months. Job creation also strengthened in July, with the latest increase in payroll numbers the fast...

Readmore

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.

  • Latest Post

  • Popular

  • Links

  • Events

Advertisement

Looking for a career in the Valve Industry?

ValveCareers Horiz

To learn more, watch the videos below or visit ValveCareers.com a special initiative of the Valve Manufacturers Association