Rolltainer Capital Project investigation

Introduction

One of South Africa’s biggest retailers contacted us this year in response to their RFI relating to the tendering process for the acquisition a large new fleet of rolltainers to be used in their supply chain throughout South Africa. The objective was to establish whether they were fit for purpose.

Our work was critical in the decision-making process for the retailer – their proposed investment was significant, and the rolltainer they procured would need to last them for a good couple of years.

Five different rolltainers were supplied for our evaluation, from three different potential suppliers.
Ideally a comparison between the submissions made by the tendering parties should be evident from the results. However, as none of the samples submitted were prototypes manufactured in direct response to the product requirements set by the new tender, a direct comparison was challenging. In addition, some of the rolltainers has been in use and some had not.

Investigation

One Eighty’s methodology

One Eighty established four categories of assessment for the rolltainers:

  • Mechanical design assessment
  • Corrosion inhibition system evaluation
  • Welded joint analysis
  • Tests on fully assembled rolltainers

Mechanical design assessment

Initially, a description and overall impression of the mechanical designs submitted by each tendering party was presented. Subsequently, an assessment of the designs was offered in relation to the following categories:

  • Load bearing ability
  • Shape and dimensions
  • Packing methods
  • Movement
  • Usability and safety

Bent caster

Additionally, a report on the observations made during a site visit to one of the local manufacturers was presented, where the equipment was observed in service. Recommended improvements were highlighted.

Corrosion inhibition system evaluation

The approach here involved two evaluations:

  1. Thickness measurement
  2. Accelerated corrosion testing by means of a neutral salt spray test

Welded joint analysis

A selection welded joints from the rolltainers was made available for evaluation in accordance with ISO 5817: Welding — Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded) — Quality levels for imperfections.

Each welded joint was sectioned and prepared for metallographic examination to reveal any weld defects, and where applicable an evaluation or recommendation was made by One Eighty.

Additionally, a hardness traverse test was completed on some of the welded joints to evaluate the mechanical integrity.

Analysis of fully assembled rolltainers

The testing procedures needed to subject the equipment to conditions similar to those that they might encounter in service in a supply chain operation. The results of the tests should have enabled a comparison between various rolltainer models as well as offering verification that the rolltainer’ s physical performance complied with the equipment capabilities advertised by the manufacturers.

Analysis of fully assembled rolltainers

The tests were as follows:

  1. Static Distributed Load Bearing Test
  2. Static Point Load Test
  3. Dynamic Load Bearing Test on a flat rough surface
  4. Static Loaded Toppling Test

Each rolltainer was specified to have a ‘maximum safe working load’ by the designer and manufacturer. The test methods described below in each case incrementally applied a load from zero up to 120% of the specified maximum safe working load (the design load). This offered insight into the load bearing ability of the equipment in a scenario where a unit was overloaded or raised by a fork lift at full load.

The acceptance criteria for each test were evaluated by thorough visual inspection. Any indication of bending, buckling, cracking, tearing, collapsing or breaking was considered a mechanical failure.

What We Found

Results

Mechanical design assessment

It was clear from our investigation that all the designs had been thoroughly considered and that the developers had made an effort to optimise the configuration of each unit’s components to produce strong, light-weight, usable, reliable, and safe products.

Some recommendations were presented, which One Eighty suggested would improve the current designs. These recommendations stemmed primarily from a distribution centre site visit where operational issues and defects were observed.

Corrosion inhibition system evaluation

  • The thickness of the corrosion inhibition layers on all three rolltainers were within the requirements of the standard.
  • The performance of the rolltainers (structural steel) after salt spray testing shows that the corrosion inhibition system was appropriate according to the standard; each showed no signed of red rust after 192 hours of neutral salt spray testing.
  • The wheel of one of the rolltainers seized after 192 hours of salt spray testing due to corrosion on the shaft and bearings. A detailed metallurgical analysis was recommended to investigate the severity of this problem.

Welded joint analysis

Two of the welded joints were found to have unacceptable hardness in the heat affected zone. In these type of weld joints, hardness is controlled by decreasing the cooling rate directly after welding.

Numerous other welding defects were observed in weld sections taken from each of the four rolltainer samples. These welding defects undermine the structural integrity of the rolltainer structures and we recommended that they should be minimised wherever possible. No direct conclusion could be made as to which rolltainer has better welds.

Various methods can be used to improve the quality of the welded joints. We recommended that focus must be given to controlling of heat input, proper cleaning and preparing of welded joints, controlling of cooling rate after welding.

Conclusion

One Eighty always recommends that any manufacturing facility wishing to improve the quality of their welding should consult a professional welding engineer to conduct a full process audit with the intension of optimising all welding practices.

An example of some of the findings in the welded joint analysis is below:

findings in the welded joint analysis

findings in the welded joint analysis

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