When materials are transported as solid bulk cargo by sea, understanding their potential hazards is an important part of safe transportation. One potential hazard is the ability of a cargo to corrode the carbon steel structures it contacts during transport.
For these materials, the International Maritime Solid Bulk Cargoes (IMSBC) Code provides criteria for identifying cargoes that are Materials Hazardous only in Bulk (MHB), including materials presenting a corrosion hazard, identified as MHB (CR).
Testing for this hazard is based on the principles of the UN Manual of Tests and Criteria Test C.1, Corrosion to Metals, but the procedure has been refined specifically for evaluating solid bulk cargoes.
Dell Tech has experience performing this refined MHB (CR) corrosion testing for solid bulk materials.
What is the IMSBC Code?
The IMSBC Code, published by the International Maritime Organization (IMO), establishes requirements for the safe stowage and shipment of solid bulk cargoes by sea.
Some solid bulk cargoes may not meet conventional dangerous-goods classifications but can still present hazards when transported in large quantities. These are identified under the IMSBC Code as Materials Hazardous only in Bulk (MHB).
One of the MHB hazard categories is CR, or Corrosive Solids, which addresses solid bulk cargoes capable of presenting a corrosion hazard to the ship’s structures.
Why is a Refined Corrosion Test Used?
The traditional UN Test C.1 – Corrosion to Metals is used to evaluate the corrosive effect of a substance on metal. The method was developed for liquids and solids that may become liquid during transportation rather than dry solid bulk cargoes.
Applying the same general corrosion-testing concept to a bulk solid creates additional considerations. Properties such as moisture content, particle size and bulk density can influence the conditions under which the solid material contacts the steel surface.
The IMO therefore developed guidance for a refined MHB (CR) test specifically addressing the testing of solid bulk cargoes.
What is the Refined MHB (CR) Test?
The refined MHB (CR) procedure exposes carbon steel test coupons to a representative sample of the solid bulk cargo under controlled conditions.
Like the standard UN C.1 method, coupons represent different potential modes of exposure to the test material, including complete contact, partial contact and exposure above the material. Testing is performed at elevated temperature and the coupons are subsequently evaluated for corrosion.
How Does the Refined MHB (CR) Test Differ from Standard UN C.1?
While the two procedures share the same fundamental corrosion-testing approach, there are several important differences.
Carbon Steel Only
Standard UN C.1 evaluates corrosion toward both steel and aluminum.
For the refined MHB (CR) procedure, carbon steel is the relevant substrate. This focuses the assessment on corrosion of the material used for ship cargo holds.
Moisture Content
Moisture is particularly important when testing a solid bulk material because it can influence the interaction between the cargo and the steel surface.
The MHB (CR) methodology has therefore included specific requirements concerning the moisture content of the test material. In the original procedure, the sample was required to contain at least 10% moisture by mass, with water added where necessary.
The refined IMO guidance further addresses how moisture should be representative of the cargo’s shipping condition, recognizing moisture as an important test parameter rather than treating the solid sample in the same manner as a liquid test substance.
Particle-Size Distribution
The refined procedure also considers the particle-size distribution of the bulk material.
This is an important distinction from conventional UN C.1 testing because a bulk cargo may contain large particles that affect how representative contact between the test material and steel coupons can be achieved. The refined guidance includes provisions for preparing solid samples where oversized material is present.
Representative Bulk Density
Another consideration specific to solid cargo is bulk density.
Rather than simply filling the test vessel without regard to the physical condition of the sample, the refined MHB (CR) procedure considers the bulk density of the cargo so that the material in the test cell appropriately represents the cargo being evaluated.
What Does This Mean for Solid Bulk Cargo Testing?
The refined MHB (CR) test does not replace the fundamental principles of UN Test C.1. Instead, it adapts the corrosion-to-metals approach for the physical characteristics of solid bulk cargoes.
Many aspects of the laboratory setup remain similar between the two procedures, including the use of at least 1.5 L of test material per reaction kettle, three different coupon exposure positions (submerged, half-way, and suspended above the sample), elevated-temperature exposure and evaluation of corrosion following testing by mass loss and pitting.
The significant differences are concentrated in the aspects necessary to make the test suitable for a solid bulk cargo:
- Carbon steel is evaluated rather than both steel and aluminum
- Moisture content of the solid material is specifically addressed
- Particle-size distribution is considered during sample preparation
- Bulk density is controlled to appropriately represent the cargo
These refinements allow the basic UN C.1 corrosion-testing concept to be applied more appropriately to materials transported as solid bulk cargo.
MHB (CR) Testing at Dell Tech
Dell Tech has experience conducting the refined MHB (CR) corrosion test for solid bulk cargoes.
For companies evaluating materials for shipment under the IMSBC Code, laboratory testing can help determine whether a cargo meets the applicable corrosion criteria and provide the data needed to support its assessment.
Need corrosion testing for a solid bulk cargo? Contact Dell Tech to discuss your material and applicable testing requirements.
Blog Author
Kate Hatherley
Katherine supports analytical testing in Dell Tech’s Lab Services. Prior to joining Dell Tech’s Lab Services Group in 2019, Katherine worked in project administration and geographic information systems in the Ontario forestry industry.
