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Sampling & Inspection

Getting the measure of bulk materials

U

K-based Stewart Group, with exper tise in international

inspection and an analysis of bulk materials, earlier this year enhanced its European activities with the opening of a new inspection site in the heart of Nordenham Port, Germany. The move will help to en-

sure that the company is able to provide fast, effective and high-quality on-site services at a number of key German ports. The new 24-hour site is in

addition to Stewart’s exist- ing Hamburg laboratory, be- ing fully equipped to pro- vide a wide-ranging service for solid fuel and concen- trate materials, including moisture and weight deter- mination, screen sizing, crushing and final sample preparation. Each of these operations

is managed by experienced surveyors who are experts in the inspection of a wide va- riety of solid fuels, ferro-al- loys, concentrates and ores.

Full services

Stewart Group already has extensive services available in Germany, with multiple sites offering full services relating to all the aforemen- tioned bulk cargoes as well as precious metals and base metals. Additional services include marine inspection, discharge and loading super- vision and stockpile sam- pling. Chris Walker, managing

director, inspection & analy- sis division, commented: “This addition to our Ger- man network is part of our continued commitment to increase our global coverage and our ability to provide the highest quality of services in the locations where our cus-

Inspection services carried out on dry bulk cargoes not only gauge consistency and quality but often, in the case of large tonnages loaded to or from ships, total weight as well – as a means of verifying the value of the bulk consignment. Here we report on the latest methodol- ogy in the quest to obtain a representative sample

tomers have the greatest de- mand. “We are well positioned

to effectively service all North German ports and the solid fuel markets they sup- port.” The new facility is lo-

cated at the Rhenus Midgard Terminal in Nordenham and will also provide inspection, sampling and sample prepa- ration services to the port of Wilhelmshaven.

To weigh or not ?

For over a century, draft sur- veys have been internation- ally accepted as an accurate and convenient means of es- tablishing the weight of bulk cargoes, providing the basis for the preparation of bills of lading and assessing various charges and port fees. Based on Archimedes’ buoyancy law, cargo weights are cal- culated by assessing changes in the level or draft of the ship before and after cargo is unloaded. Guidelines for such cal-

culations are laid down in United Nations’ ECE/EN- ERGY/19, “Rules of trans- portation of cargoes – Draft Survey Code Recommenda- tions.” However, to gain meaning-

ful and reliable data, the draft surveyor or shipmaster has to apply a wide range of some- what complex correction fac- tors to draft readings. These have to take into

account changes in environ- mental conditions such as water density, together with

Stockpile sampling is among the wide range of services available from Stewart Group’s new inspection site at Midgard Terminal, port of Nordenham

ship related factors includ- ing heel, trim and hull defor- mation characteristics. Buoyancy tank content

changes and storm water in- take can also have a marked effect on results.

Limitations

Unfortunately accuracies us- ing this methodology can vary considerably and it is not uncommon for errors of ±5% or higher to occur. Sub- jective rather than qualita- tive reasoning can play a major part in this and sur-

veyors may call upon per- sonal experience to arrive at final readings. As a result, discrepancies

in draft survey results can give rise to commercial dis- putes amongst sellers, ves- sel operators, buyers and surveyors relating to which weight values to accept for payment of the cargo, port fees and other charges. For cargoes with low ton-

nage value, these levels of accuracy may be deemed ac- ceptable, but for companies purchasing higher value

goods, errors can be expen- sive. This has led companies to implement other more re- liable and accurate methods of measuring received cargo quantities. A clear advantage of the

draft method is that calcula- tions can be done relatively quickly, minimising opera- tional delays in unloading and therefore cutting demur- rage costs. Consequently any alternative methods need to be operationally ef- ficient, accurate and provide traceable results in the case of discrepancies or disputes.

Weigher accuracy

One such method is to bulk weigh goods as they are un- loaded. There are various techniques available, with the choice depending on the type of products involved

and their properties. It should be noted that it is important that such weigh- ing systems should be suit- able for Weights and Meas- ures approval so that data can be used in the case of disputes. (The UK Weights and Measures Regulations refer to the suitability of such approved weight data for expert witness use in the case of legal dispute.) For bulk solids such asss

grain and sugar, belt weigh- ers can be an effective solu- tion for verifying unloaded quantities. These provide an accurate method of totalising material as it is offloaded and systems can be selected to provide the necessary weights and measures approved weight data. Belt scales operate by

BMI March/April 2010

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