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Monitoring Valve Health via the Internet

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Industry Headlines

U.S. Jobless Claims Fall to Near Five-Month Low

Thursday, 20 July 2017  |  Chris Guy

In the week ending July 15, the advance figure for seasonally adjusted initial claims was 233,000, a decrease of 15,000 from the previous week's revis...

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How to Choose the Best Rapid Prototyping Method

How to Choose the Best Rapid Prototyping Method

Tuesday, 18 July 2017  |  Kate Kunkel

As new products are designed, including valve bodies and the parts that comprise the finished valve, prototypes must be created. How that is achieved ...

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Industry Headlines

Badger Alloys Joins VMA as Associate Member

1 DAY AGO

This week the Valve Manufacturers Association (VMA) welcomes Badger Alloys as an official associate supplier member. This is VMA’s fourth new member in 2017.

Located in the heart of Milwaukee and founded in 1966, Badger Alloys offers single source capabilities for custom castings. The company pou...

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Thermodyn Joins VMA as Associate Member

1 DAY AGO

This week the Valve Manufacturers Association (VMA) welcomes Thermodyn Corporation as an official associate supplier member. This is VMA's third new member in 2017.

In 1979, Thermodyn began business with the dual purpose of selling A.W. Chesterton products and manufacturing high-temperature elastomers ...

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EPA Selects Projects for Water Infrastructure Loans

-1 DAYS AGO

The EPA is inviting 12 projects in nine states to apply for Water Infrastructure Finance and Innovation Act (WIFIA) loans. These potential applicants were selected from a group of projects that represent large and small communities from across the U.S. that submitted letters of interest to EPA in Ap...

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U.S. Shale Oil Production Growth to Slow in 2018

21 HOURS AGO

In its newly released North America Watch , ESAI Energy projects that by the end of 2017, U.S. shale oil production will hit 5.6 million b/d, over 1 million b/d higher than at the end of 2016. But the pace of growth will slow in 2018 as current oil prices below $50 per barrel are likely to put a check...

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U.S. Jobless Claims Fall to Near Five-Month Low

-1 DAYS AGO

In the week ending July 15, the advance figure for seasonally adjusted initial claims was 233,000, a decrease of 15,000 from the previous week's revised level. The previous week's level was revised up by 1,000 from 247,000 to 248,000. The 4-week moving average was 243,750, a decrease of 2,250 from t...

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Empire State Manufacturing Survey Dropped in June

1 DAY AGO

Business activity grew modestly in New York State, according to firms responding to the July 2017 Empire State Manufacturing Survey. Manufacturing firms in New York State reported that business activity continued to expand in July. After reaching its highest level in more than two years last month, ...

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Checking Metal Materials With a Magnet

materials_q_and_a_graphicQ: I’ve seen people checking metal materials with a magnet. Is this a useful method of sorting materials, and if so, how does it work?

A: Valve companies deal with a large number of pure metals and alloys due to the variety of applications in the process industry. Occasionally, alloy identification must be performed on parts due to customer inquiries, mix-ups in bar stock, questionable machining characteristics or for some other reason. Although positive material identification (PMI) has become quite common, a PMI tester is not always available in a timely manner. One common identification/sorting technique that is often overlooked—and sometimes misapplied—is magnetic inspection. Magnetic inspection can save a lot of time by quickly proving a material is not what it is supposed to be.

Categorizing Materials by Magnetic Attraction

Magnetic inspection refers to categorization of a material by observation of its magnetic attraction force. Various alloy groups behave differently when exposed to a magnet. However, virtually all alloys fall into one of four behavior categories:

  • F - Fully magnetic:Materials such as carbon steels, alloy steels.
  • N - Never magnetic: Materials such as aluminum alloys, copper alloys, most nickel-base alloys, some stainless steels, etc. These materials exhibit no perceptible attraction to a magnet.
  • P - Partly magnetic: Materials such as some stainless-steel castings and wrought products. These materials exhibit some attraction to a magnet, but less than the fully magnetic materials.
  • V - Varying:Materials such as some stainless steels, nickel-copper alloys, etc. These materials may or may not be attracted to a magnet, and when attracted to a magnet, the attraction strength may vary significantly, depending upon the exact composition and processing history.

Information on magnetic characteristics can usually be found in material product literature.

An unknown material’s magnetic characteristic is determined by placing a magnet against the material and observing whether it is attracted or not. If there is no perceptible attraction, the material falls into category “N”. If there is attraction, decide whether it is full or partial. This is best done by placing the magnet against the unknown material and then bringing a piece of carbon steel into contact with the opposite end of the magnet. If the carbon steel easily removes the magnet from the unknown material, then the unknown falls into category “P”. If the magnet is attracted with approximately equivalent force by both materials, then the unknown falls into category “F”. In performing this comparative test, it is important that the surface contour and finish of the unknown piece and the carbon steel piece be the same (preferably flat). It is also important that both parts are more massive than the magnet or, in the case of sheet materials, that both parts have approximately the same thickness.

Limitations of Magnetic Inspection

The most important thing to keep in mind regarding magnetic inspection is that, although it can prove that a part is not a particular material, it cannot prove that a part is a particular material.

Here are some example applications of magnetic inspection:

  • Example 1: Records have been lost for a valve shaft that has been stored for several years. It is assumed the shaft is probably either S17400 or S20910, since these are the standard materials of construction for this part. Magnetic inspection determines that the shaft is fully magnetic. S17400 is fully magnetic, whereas S20910 is never magnetic. Therefore, the shaft is not S20910, and may be S17400. It could also be some other fully magnetic material.
  • Example 2: A customer orders a “316” valve body, but upon receipt of the body finds that it is slightly magnetic. The customer calls and complains that he did not receive a “316” body as ordered, because he knows that 316 stainless steel is never supposed to be magnetic. The problem with this logic is that the body is not 316, but rather is a CF8M casting, the equivalent of 316 wrought material. The chemistry of the cast material is adjusted to intentionally produce a small percentage of “ferrite,” which is a magnetic phase. This renders the casting partly magnetic, and often leads to this type of confusion. This highlights the importance of accuracy in material designation and product form (cast, wrought, etc.) when using magnetic inspection.
  • Example 3: A casting is sent to inspection for a material check because the machine operator noticed its machining characteristics were unusual. The casting is supposed to be CW2M. Magnetic inspection may save a great deal of time vs. performing a PMI. The casting is found to be partly magnetic. This proves that the casting is not CW2M, which is never magnetic.
  • Example 4: Same situation as example 3. This time, the material is found to be non-magnetic. This does not mean that the material is CW2M. This is one of the most important limitations in magnetic inspection. Magnetic inspection can prove that a part is not a particular material, but it cannot prove that a part is a particular material. In this case the casting should be further evaluated by PMI or some other method to determine if it is CW2M or some other non-magnetic material.

Remember that magnetic inspection can be a valuable, time-saving technique, but if used improperly it can produce erroneous identification of materials.

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