Steel Applications

Steel is made resistant to corrosion with electro galvanizing or hot-dip galvanizing. To ensure that the zinc surface fulfills its purpose, coating thickness and mechanical properties must be tested. FISCHER offers reliable analytical devices for rust-protection coatings. In addition, you will also find instruments for material testing of stainless steel, for example to measure ferrite content.

Steel applications

Application notes

Hot-Dip Galvanization as Corrosion Protection

For protection against the elements, exposed steel parts require an anti-corrosion coating such as hot-dip galvanization. To this end, a new directive for CE labelling of steel products and their corrosion protection will become effective in 2014. Product liability will be significantly tightened and manufacturers will be obligated to verify the thickness of the hot-dip galvanization.

Life is about to change for manufacturers of metal and steel structures. Beginning in 2014, a new CE labelling standard for steel products and their corrosion protection will shift product liability – i.e. the burden of proof for documenting coating thickness measurements – to the providers of the coating systems. For many in this field, only the most user-friendly and cost-effective measure­ment technologies will come under consideration.

Fig.1: Compact pocket-sized instruments of the MP0/MP0R family

The FISCHER MP0/MP0R product family meets precisely these needs and requirements. Due to their compact design and simple four-button handling, these instruments are flexible in on-site applications and require no costly user training. The two displays allow for easy reading in various operational positions. Visual and acoustic signals inform the user when the measurement is complete.

The hard metal probe tips are a special feature that guarantees significantly longer lifetime, even on rough surfaces. Measurement results can be easily transferred to a computer for evaluation, recording and storage using the convenient FISCHER DataCenter software.

Solutions are also available for more demanding requirements, for example the measurement of hot-dip galvanized coatings underneath a layer of paint. Specifically for this purpose, FISCHER has developed the FDX13H probe. Used in combination with the FMP instruments, it can determine the thickness of both the zinc and paint coatings in one “duplex measurement” step; the readings are displayed separately. FISCHER has thereby succeeded in simplifying for the user an extremely complicated metrology procedure, simul­taneously presenting the results of two different physical measurement principles in one easy operation.

Whether the compact and cost-effective MP0/MP0R gauges or the powerful FMP models with exchange­able probes, FISCHER has the right high-precision instrument for determining the thickness of hot-dip galvanized coatings. Your local FISCHER repre­sentative will be happy to answer any questions you may have.

Measurement of the ferrite content in (duplex) steel and weld seams

Components found in industrial plants – whether chemical, energy, petrochemical or other – are often subject to heat, aggressive agents and high pressure. These conditions demand steel types that are extremely corrosion and acid resistant even at high temperatures. When austenitic steels are used, it is important to make sure the ferrite content of the weld seams is within strict norms, because only the optimal ferrite content can ensure the best corrosion protection. For this reason some industries have set standards, specifications and regulations for ferrite content.

Fig.1: Measuring the ferrite content of a weld seam with FERITSCOPE® FMP30 and the probe FGAB1.3-Fe

During the welding of joints on e.g. boilers and pipelines made of austenitic steel, the heat causes modifications in the crystal lattice structure which lead to the formation of ferrite. Weld seams that are poor in ferrite do not have as much yield strength, but too much ferrite reduces their fracture toughness, ductility and corrosion resistance, so it is important that the welding process produces just the right amount.

With duplex steel in particular, the ferrite content in the heat affected zone can easily deviate from the target values, either due to unsuitable filler materials or through incorrect heat input or cooling during the welding. Only onsite spot measurements can provide assurance that the processing did not change the ferrite content at the expense of crucial mechanical or corrosion-resistance properties.

To meet these requirements FISCHER has developed the handheld FERITSCOPE® FMP30 instrument, which measures the ferrite content using the magnetic induction method and displays it either as percent ferrite content or as a WRC (Welding Research Council) ferrite number The FERITSCOPE® FMP30 can be outfitted with a variety of probes in special shapes such as axial, angled or for measuring inside centre holes.

Fig.2: Highest corrosion protection is required, for example, for pipelines and boilers in the chemical or petrochemical industry

The FISCHER FERITSCOPE® FMP30 allows for reliable and precise determination of the ferrite content in percent or as a WRC ferrite number. For further information please contact your local FISCHER representative.

Determination of the α-martensite content in steel tanks used for storing liquid hydrogen

New technologies have become more important than ever for developing efficient and clean energy supply systems. Hydrogen technology is one example that holds high potential both as an accumulator and as a fuel. However, cryogenic liquid hydrogen is typically stored in special steel tanks – a circumstance that presents its own safety challenges: Should the structure of the tank fail in any way, the hydrogen can escape uncontrollably and form inflammable mixtures with other elements like oxygen present in the air. Therefore, material testing is absolutely essential in any quality control process for tanks used to store liquid hydrogen.

Austenitic steel is often used as a base material for producing hydrogen storage tanks. However, the face-centred cubic (FCC) crystalline structure of the alloy is only metastable. Indeed, the manufacturing process itself (cold rolling or forming) can cause the FCC crystals to transform into the body-centred tetragonal (BCT) microstructure of martensite.

Also dropping below the MS (martensite start) temperature can be problematic. When allowed to cool slowly, the austenite transforms into a mixture of ferrite and cementite. But in a rapid cooling process (i.e. quenching, employed to harden the steel), there is no time for the carbon atoms to diffuse out of the crystalline structure in large enough quantities to form ferrite and cementite, resulting in martensite.

Too much martensite is undesirable in steel destined for hydrogen tanks, because hydrogen can settle at the grain boundaries of the martensite (hydrogen embrittle­ment or cold cracking), which can then lead to material failures. Therefore, testing the steel’s martensite content with precise measurements is required to determine its suitability for this purpose.

An easy-to-use technique is the magnetic induction measurement method. The FERITSCOPE® FMP30, originally designed by FISCHER to measure the ferrite content of steel, has now been further enhanced to additionally measure the martensite content. The switch-over to “martensite testing mode” entails just a few clicks in the software.

Fig.1: FERITSCOPE FMP30 with probe FGAB1.3-Fe to determine martensite content

The calculation of the martensite content from the probe’s signal is based on the relations published by Talonen et al. (Comparison of different methods for measuring strain induced α-Martensite content in austenitic steels, Materials Science and Technology, Dec. 2004).

In order to assess the potential risk of material failure and avoid subsequent damage, it is quick, easy and cost-effective to determine the α-martensite content in hydrogen tanks using the FERITSCOPE® FMP30. Please contact your FISCHER representative for more information.

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Fischer Technology Inc.
Windsor/United States

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