Annex - Guidance for Conducting the Refined MHB (CR) Test
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Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC.1/Circular.1600/Rev.1 - Guidance for Conducting the Refined MHB (CR) Test - (28 April 2022) - Annex - Guidance for Conducting the Refined MHB (CR) Test

Annex - Guidance for Conducting the Refined MHB (CR) Test

 Background

1 Based on the detailed test protocol used by the Global Industry Alliance (GIA) for undertaking the refined MHB (CR) test and the points outlined in sections 3.1 to 3.3 of the GIA report (CCC 5/INF.18), general guidance for conducting the refined MHB (CR) test on any solid bulk cargo was developed. The aim was to ensure a clear understanding of the parameters that influence the test results and to provide advice on how to conduct the experimental procedure, given the range of physical and chemical properties of solid bulk cargoes.

Introduction

2 This Guidance extends and details the MHB (CR) test method for assessing solid bulk cargo materials against the "corrosive solids: MHB (CR) hazard" as described in paragraph 9.2.3.7.3 of the IMSBC Code. The test should be conducted on representative samples of the cargo at conditions representing their as-shipped properties. It should be utilized by test laboratories conducting the test in conjunction with the MHB (CR) test description (paragraph 9.2.3.7.3 of the IMSBC Code) and the UN C.1 test procedure (UN Manual of Tests and Criteria, section 37.4). The method is an accelerated corrosion test run at 55°C that assesses the resistance of carbon steel test coupons to corrosion due to exposure to a solid bulk cargo material. The test duration should be a minimum of seven days, which may be extended to 14, 21 and 28 days, in accordance with the existing UN C.1 test protocol. Each test should be conducted to ensure acceptable repeatability. The scope of the refined MHB (CR) test is limited to and identical to that of the MHB (CR) test, as described in 9.2.3.7.3 of the IMSBC Code.

Steel coupon details

3 This section specifies the steel coupons and their preparation:

  • .1 Steel coupon type

    At least three steel coupons with nominal dimensions of 20 mm x 50 mm x 2 mm should be used in each test. The type of steel should be as specified in paragraph 9.2.3.7.3 of the IMSBC Code. Aluminium coupons should not be tested, as solid bulk cargoes are not shipped in ships with holds constructed of aluminium.

  • .2 Grinding and cleaning

    The steel coupons should be progressively wet ground on both sides and on all four edges, to a minimum finish of 120 grit. The coupons should then undergo ultrasonic cleaning in deionized water, rinsed with high purity ethanol or acetone and immediately dried with high purity gas (e.g. nitrogen). No chemical surface preparation (pickling, etching, etc.) should be performed to prevent surface "irritations" (inhibition, passivation) and no cleaning performed with detergent, alkali or other proprietary means.

  • .3 Dimension measurements and weighing procedures

    Coupons should be identified with a suitable marking system in accordance with relevant international standards and best practices. Any stamped or etched regions should be avoided during the assessment of localized corrosion. The dimensions of each coupon, i.e. length, width and thickness, and its weight should be recorded. The dimensions should be measured to 0.1 mm. The weight should be measured to 0.0002 g.

  • .4 Steel coupon storage

    After recording the dimensions and weight of each coupon, the coupons should be rinsed with high purity ethanol or acetone and dried with high purity gas. If the coupons are not immediately used in a test, they should be appropriately stored prior to testing (e.g. stored in a desiccator to lower relative humidity and to avoid adventitious contamination), ensuring that coupons are kept isolated from each other. After storage and prior to testing, the coupons should again be rinsed with high purity ethanol or acetone and dried with high purity gas. Should any sign of corrosion be visible at this point, e.g. stains at the surface, the coupon should be wet ground again, using a minimum of 120 grit paper followed by the ultrasonic cleaning, rinsing, drying and measurement (size and weight) procedures described in paragraphs 3.2 and 3.3 above.

Test set-up guidance

4 The test set-up section outlines the details of how to prepare a representative sample and load it into the test cell with coupons:

  • .1 Sample

    A representative sample of the cargo should be sourced and subsampled for testing. The representative sample should be tested at typical as-shipped cargo carriage conditions including moisture content, bulk density, particle size distribution and atmospheric conditions. The shipper should provide the typical as-shipped cargo conditions or inform the laboratory when data is not available. Where pH is known to or expected to affect the testing outcome for a particular cargo material, the pH of the sample should be measured before and after testing in accordance with relevant international standards, and the pH should be reported by the laboratory. It should be ascertained that the pH during testing is representative of the material's pH in the as-shipped condition.

  • .2 Particle size distribution (PSD)

    For cargoes which only contain fine particles, the material should be tested as such. For cargoes that contain a mixture of large and fine particles, where the maximum top size is greater than 25 mm, some modification of the particle size distribution may be needed in order to fit the sample into the test vessel. If the amount of +25 mm particles is small (~10%), this material can be screened at 25 mm and the finer fraction used as the representative sample for testing. If the amount of +25 mm is greater than 10%, sample reconstitution methods should be employed. Methods for both coal and bauxite are given in appendix 2 to the IMSBC Code. These should be used as guides for other cargoes that would have similar particle size distributions and therefore would need sample reconstitution approaches to be applied. For cargoes that are solely made up of coarse particles (e.g. lumpy iron ore, pig iron, hot briquetted iron, etc.) the representative sample should be crushed to achieve enough material that is -25 mm and +6.3 mm for testing. If the particle size distribution of a sample causes practical problems while executing the test, the laboratory should consult the shipper regarding its properties and the best method to modify the particle size distribution, so that it may be adequately tested.

  • .3 Moisture

    The sample should be tested at the as-shipped moisture content provided by the shipper. Based on practical experience, the shipper should consider the possibility of moisture addition that may occur during loading and shipping, e.g. due to adverse weather conditions. The moisture content of the sample should be checked after completing any particle size distribution modifications (as outlined in paragraph 4.2). The moisture content of the sample should be measured just prior to testing and this should be reported.

  • .4 Bulk density

    The sample, after any particle size modification has been made, should be placed into the test cell such that at least 1.5 L of material is used. For coarse or lumpy materials, the bulk density requires specific consideration. For such materials, a mark at a known volume is to be placed on the cell and the weight of sample that corresponds to its bulk density multiplied by that volume is to be added to the cell such that it fills the cell to the mark. If the shipper has no information on the as-shipped bulk density of the cargo, the laboratory should determine the bulk density in accordance with applicable ISO standards, including the method described in Uniform method for measurement of the density of bulk cargoes (MSC/Circ.908).

  • .5 Coupon placement

    All coupons used in the test are to be orientated in the vertical position. One coupon should be fully buried in the test sample and be placed in the sample during the loading of the sample. One coupon should be half-buried in the top layer of the sample and be placed in the sample during the final stages of loading the sample. The final coupon should be suspended in the gas phase. Placement of the buried coupon should be such that its lower edge does not touch the bottom of the test vessel. The minimum distance between the upper edge of the fully buried coupon and the top of the test sample should be 10 mm. For some coarser samples, the fully buried coupon may need to be placed deeper to the sample to ensure it is held in place, vertically by sufficient particles.

  • .6 Atmosphere

    The test vessel with steel coupons and sample should be closed with a fitted glass lid equipped with a reflux condenser. All remaining openings in the lid are to be closed using ground glass stoppers. The top of the condenser is to be set to represent the atmospheric carriage conditions of the cargo being tested. The lid is to be effectively sealed in order to ensure that no loss of moisture occurs during the test. Information on the as-shipped cargo space atmosphere should be provided to the laboratory by the shipper. For cargoes that react with oxygen and/or are shipped with an inert gas blanket, the test should be conducted with inert gas content and the top of the condenser closed. For cargoes where atmospheric conditions during shipping demonstrate strong oxygen depletion, the top of the condenser may be closed to better reflect the cargo carriage conditions. In all other cases and for all other cargoes, the test should be conducted with an open condenser to allow for air exchange.

Conducting the test

5 The test temperature (i.e. the temperature of the sample in the test vessel) should be 55°C (55°C ±1°C). The test vessel should be heated using an appropriate, controllable method and the temperature of the test material monitored, checked and recorded regularly throughout the test. Heating should be achieved evenly through the sample material and the test temperature should, where practicable, be reached within one hour. The laboratory should document the details of the heating procedure.

Post-exposure treatment of the coupons and analysis

6 Post exposure treatment of the coupons and analysis should be as follows:

  • .1 At the completion of the test, the vessel should be allowed to cool to room temperature.

  • .2 The steel coupons should be carefully recovered and any excess sample material adhering to the coupons removed by hand, followed by inhibited pickling using a suitable procedure for corroded steel coupons in accordance with relevant international standards (e.g. ASTM G1-03).

  • .3 If necessary, inhibited pickling should be repeated, until coupon mass becomes constant, as per guidance in relevant international standards.

  • .4 Both coupon surfaces are to be photographed before and after inhibited pickling.

  • .5 After final cleaning with alcohol and acetone in an ultrasound bath and once dry, the test coupons should be weighed.

  • .6 Disposable plastic gloves should be worn at all times when handling the test coupons.

  • .7 The coupon weight should be used to determine the mass loss in grams and as a % of the original mass. Any inhibited pickling weight loss from unexposed carbon steel reference coupons should be subtracted. The general corrosion rate should be calculated from the mass loss, the coupon dimensions and the exposure time.

Qualification of localized corrosion

7 After removal of corrosion products, coupons are to be analysed on both sides to identify the occurrence of localized corrosion. Localized corrosion identification and qualification is to be conducted using national and/or international corrosion standards (such as NACE/ASTM G193-12d).

Quantification of localized corrosion

8 When localized corrosion occurs in tandem with, or instead of, uniform corrosion attack of the surface, the depth of the deepest intrusion should be determined. The maximum measured loss of thickness (from the general corrosion rate measured by weight loss) is to be added to the depth of the deepest intrusion to determine the intrusion depth. The deepest intrusion is to be determined metallographically or using surface profilometry or other suitable methods, as outlined in relevant nationally or internationally accepted standards, such as ISO 11463:1995 and ASTM G46.

Parent topic: MSC.1/Circular.1600/Rev.1 - Guidance for Conducting the Refined MHB (CR) Test - (28 April 2022)
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