21/06/2018

Special requirements of construction materials for dangerous goods packagings

Packagings and large packagings for the transport of dangerous goods must be tested for their compatibility with the respective filling materials.

Generally, the user of a package must meet these requirements in his own responsibility, whereby the packaging manufacturer will generally provide corresponding advice.

Regulations require that the chemical compatibility of liquid substances with packagings made of plastics must be proven as early as the type test performed on prototypes, whereby each of the respective goods are prestored in a predamaged condition half a year beforehand at room temperature.

In the case of the most frequently used plastics, – high molecular weight high density polyethylene and medium molecular weight high density polyethylene (HMW HDPE and MMW HDPE), – this half year prestorage can be reduced to a three week prestorage period at a temperature of 40°C. Here the required proof is generally provided by using so-called standard liquids that serve as representatives for the different types of damage effects (swelling, stress cracking, molecular deterioration and combinations thereof) that can occur with polyethylenes. Respective standard liquids have been assigned to each deterioration mechanism (see ADR 6.1.6.1 and/or
ADR-Summary 6.1.6.1):

(...)
a) Wetting Solution for substances causing severe cracking in polyethylene under stress, in particular for all solutions and preparations containng wetting agents.
(...)
b) Acetic acud for substances and preparations causing cracking in polyethylene under stress, in particular for monocarboxylic acids and monovalent alcohols.
(...)
c) Normal butyl acetate/ normal butyl acetate-saturated wetting solution for substances and preparations causing polyethylene to swell to such an extent that the polyethylene mass is increased by about 4% and at the same time causing cracking under stress, in particular for phyto-sanitary products, liquid paints and esters.
(...)
d) Mixture of hydrocarbons (white spirit) for substances and preparations causing polyethylene to swell, in particular for hydrocarbons, esters and ketones.
(...)
e) Nitric acid for all substances and preparations having an oxidizing effect on polyethylene and causing molecular degradation identical to or less than 55% nitric acid.
Nitric acid in a concentration of not less than 55% shall be used.
(...)
f) Water for substances which do not attack polyethylene in any of the cases referred to under a) to e), in particular for inorganic acids and lyes, aqueous saline solutions, polyvalent alcohols and organic substances in aqueous solution.
(...)

Without the need for further proof, the user can assign the dangerous goods summarized in the substance registry ("Assimilation List") in subsection 4.1.1.19 of ADR/RID to these standard liquids.

In an updated assimilation list (german only), the BAM has added these assignments of dangerous goods to standard liquids, and has published this list in Dangerous Goods Procedural Rule BAM-GGR 004 (german only), which shall be continuously updated to the advanced state of the art of knowledge.
The BAM has established a working group for this purpose.

Further proof of chemical compatibility of charges when a type test is being performed with one or several standard liquids can be provided through laboratory tests.
In these test, specimens made of the same moulded materials are subjected to comparative material tests using a standard liquid and a charge X, the purpose being to provide evidence that the charge X damages the material less than the standard liquid.

The "Test Regulations for Plastic Vessels", the so-called "lab methods", were developed to be able to evaluate the deterioration effects of these other filling materials with polyethylene when compared with the standard liquids. You will find these either in the RID as an appendix to Section 6.1 or in the standard EN ISO 16101 "Packaging – packagings for the transport of dangerous goods – compatibility testing for plastic packagings (ISO 16101:2004)".

The absorption of mass by swelling is investigated with the lab method A. Lab method B is a pin impression method which investigates stress crack formation. Lab method C determines possible oxidative or molecular decomposition deterioration of the polyethylene construction material. In this case, the melt flow index is determined after pre-storage with the filling material and compared with that after pre-storage with 55% nitric acid.

The BAM has created the BAM-List on the chemical resistance of sealing construction materials and metallic construction materials used otherwise predominantly in tank manufacturing. The BAM-List is extended regularly and updated with the latest technological standards. It can, if applicable, also be used for packagings.

A transfer of the knowledge gained in this way for plastics moulded materials can likewise be transferred to other moulded materials by means of comparative laboratory tests. This method is described in Dangerous Goods Procedural Rule BAM-GGR 003. (see Verification of the Suitability of Alternative Plastics Moulded Materials).