An Evaluation of Testing Methods to Detect Surface Iron Contamination

by David Frey

2Iron contamination on the internal surfaces of Zr

process equipment can cause serious corrosion

problems.

Two common methods, Ferroxyl and Copper Sulfate will be compared to a very simple water test.

Common sources of iron contamination will be discussed along with methods of iron removal and prevention.

This presentation will focus on various common testing methods to detect iron and will evaluate the effectiveness of

those tests along with the hazards associated with their use.

Sources of iron contamination and methods of removal will

also be discussed.

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Unplanned Iron Detection Test SS Expansion Joint

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Residual embedded iron is less likely to cause pitting or corrosion attack in process applications involving Nitric, sulfuric or acetic acid. However Iron contamination should always be avoided or removed.

Surface iron contamination is usually not a problem for Titanium except for concentrated hot brine applications. As a precaution, obvious iron contamination should by removed.

Why Worry About Iron Contamination?

Zr is vulnerable to ferric chloride pitting attack. Surface iron in a chlorine environment such as HCl can result in

severe pitting of Zirconium and possible SCC.

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Sources of Iron Contamination:

Forming: Rolling, Head Forming (spinning/pressing.

Fixtures & ToolingGrindingIron dustBlasting (iron contamination in sand)Handling fork lifts, trucking chainsTube Expansion (roller expanding)Hydrotesting (rust deposits from water supply (fire hydrants).

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Common Testing Methods to Detect Surface Iron

Ferroxyl TestingASTM A380ASTM B912 (modified)ASTM B650 App. X1AMS 2700 method 103

Copper SulfateAMS 2700 method 102ASTM B650 7.4.3

Alternate MethodsWater AMS 2700Head and Shoulders

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Ferroxyl Testing: Add nitric acid to distilled water and then add potassium ferricyanide in the following proportions.

Distilled water 94 weight % 1 gal 1000 cubic cm

Nitric Acid (60-67%) 3 weight % 1/5 pt. 20 cubic cm

Potassium ferricyanide 3 weight % 30 g 4 oz

Apply solution with plastic or glass spray atomizer

The appearance of a blue stain within 15 seconds of application is evidence of iron contamination.

Flush surface with water as quickly as possible after inspection to rinse off test solution. White vinegar or 5-20 weight % acetic acid may also be used.

Rinse solution should be collected for proper disposal.

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Copper Sulfate: Dissolve 8 g of copper sulfate in 500 ml of distilled water, to which 2-3 ml of concentrated sulfuric acid has

been added.

Apply solution with plastic or glass spray atomizer. Re-spray as required to keep the surface wet for a period of 6-7 minutes.

Wipe the surface dry and visually inspect for areas of deposited copper. A copper deposit will indicate the presence of iron.

Flush surface with water after inspection to rinse off test solution.

Rinse solution should be collected for proper disposal.

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Testing Precautions: Ferroxyl

Potassium ferricyanide is not a dangerous poison as are the simple cyanides. However, the solution can emit highly toxic cyanide fumes if heated to

decomposition or mixed with concentrated acid.

Rubber gloves and face shields should be used.

Avoid inhalation of atomized spray.

Not recommended for use on equipment intended for food processing or pharmaceuticals.

Solution and rinse water must be disposed of as hazardous waste.

Copper Sulfate

Rubber gloves and face shields should be used.

Avoid inhalation of atomized spray.

Not recommended for use on equipment intended for food processing or pharmaceuticals.

Solution and rinse water must be disposed of as hazardous waste.

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Test Protocol Test subject was Zr 702

elliptical head (warm formed

by spinning)

PVC spill containment

One half of the ID surface of the head received additional

surface conditioning by

grinding to provide a

reasonably smooth surface.

The other half was as

received from the head

forming company and had a

sandblasted surface profile.

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Test Protocol head was divided into 6 pie shaped sections. The as blasted half had 3 sections, one each, for Ferroxyl, Copper Sulfate and water. The half with additional surface grinding preparation was divided in the same manner.

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Test Protocol Ferroxyl, Copper Sulfate and water were sprayed onto the divided sections of each half. Adjacent sections were covered with plastic to prevent overspray.

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Test Results Ferroxyl

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Test Results Copper Sulfate

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Test Results Plain Old Water

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Test Results Side by Side Comparison note the streaks of embedded iron from the head spin forming die. Embedded iron was readily detected with Ferroxyl and water methods.

Ferroxyl Water Copper Sulfate

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Test Results unexpected crack indications revealed by Ferroxyl.

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Test Results Detection of iron dust on the surface, Ferroxyl only

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Observations and Conclusions from test results

Ferroxyl Method demonstrated the best sensitivity and detection capability.

Water testing was sufficiently capable of detecting iron small enough to be of concern for FeCl pitting.

Copper Sulfate was not much better than water testing and any residual copper that is not removed could cause

a problem with Cupric chlorides.

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Practical Recommendations Water testing method is sufficient for detecting iron in less critical

applications where FeCl pitting is not a major concern. Or for intermediate testing prior to a final ferroxyl test prior to shipment.

Water testing can be a cost effective method for large vessels and columns where Ferroxyl would be very expensive and hazardous.

End Users and Fabricators need to work together to determine the need for iron detection inspection and develop a practical inspection plan. The risks of iron contamination exist throughout the fabrication process and expensive tests such as ferroxyl should not be performed too early in the process.

Inspect after forming / prior to any HT / after hydrotesting

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Removal of Iron ContaminationNitric Pickle Mechanical Grinding

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Prevention of Iron Contamination

Production work areas should be divided so that fabrication is confined to an area with only one grade of material.

Material should be protected from handling equipment such as chains, hooks, fork lifts.

Forming equipment should be ground or wiped clean prior to any forming or rolling. Pre-clean internal metal surfaces.

Hand tools and brushes should be segregated by materials. Fixtures should have SS contact surfaces.

Personnel should avoid walking on process surfaces

Blasting sand should be iron free.

Hydrotest water should be filtered.

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Conclusions:

Testing for iron contamination is an important part of the fabrication/inspection process.

The Method of Iron Detection Testing should be based on the process application of the equipment and any processing (such as heat treatment) that is performed during fabrication.

The sequence of testing and fabrication operations should be carefully planned in order to minimize cost and to be confident that the equipment did not become contaminated prior to shipment.

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