Published in the October 2016 edition of GeoDrilling International

DOWN TO THE WIRE

Colin Rice of Colin Rice Exploration and Training (Pty) Ltd. presents some observations on steel wire rope safety

Drill-site safety has become an extremely important part of all exploration operations, and many companies have developed and implemented extensive safety management systems to identify hazards and manage risk. Despite this, many drilling operations operate illegally thanks to ignorance of some basic physical principles. One example, and a constantly recurring issue, is the use of wire ropes. Steel wire ropes are widely used on drill rigs for a number of functions, including drill string hoisting, wireline overshot deployment and retrieval and on some drills as pulldown/pullup ropes. Whatever the function of the rope, it will run over one or more sheaves (pulleys). If it is a hoist or wireline rope, it will be wound onto a hoist or winch drum. In every application, the rope can be considered a critical element of the lifting system on a drill rig.

SAFETY FIRST

Wire rope is a very complex mechanical device and ropes are available in a great number of diameters, constructions and grades, and because wire rope represents a significant hazard, a factor of safety has to be applied to its application. In South Africa and many other countries, for example, the legislated factor of safety for steel wire ropes is six. This means that in order to determine the Safe Working Load (SWL) of the rope one will divide the mean breaking load (MBL) or proof breaking load by six. In other words, if a rope has a MBL of 15 metric tonnes (t) then the maximum load that can legally be lifted with the rope is 2.5t. In terms of an NQ borehole for example, this means that we can legally pull about 315m of NQ drill rod using a single line. If the borehole is shallower than 315m, then there is no problem, but if the borehole is to be drilled deeper, then the drill string must be pulled using a double line system or using the main cylinder of the drill rig, both of which have time and cost implications for the contractor. Contractors, therefore, frequently ignore the legal requirement and pull rods below the legal limit. Adding to the comlexity, in most countries steel wire ropes are available in four different grades. Consider, for example, a 16mm IWRC hoist rope, the lowest grade will have a MBL of approximately 15t and the highest grade will have an MBL of approximately 24t. The SWL of a 16mm wire rope can therefore vary. It is very important that the contractor knows the grade of rope in use – all wire ropes must therefore be supplied with a valid test certificate that details, among other information, the MBL of the rope. It is then a simple exercise for the mining or exploration company to determine the SWL and the depth limit of the rope.

KNOW WHEN TO DISCARD

Wire ropes are used in drilling operations because they have the ability to change the direction of an applied tensile load and this is achieved by running the rope over a sheave or pulley. However, this adds another dimension of complication to the use of a wire rope. As a rope moves over a sheave it is subjected to a cyclic stress reversal and this leads to fatigue in the affected section of rope. It is clear that the smaller the sheave wheel, the greater the amplitude of the stress reversal, and so the greater the rate of fatigue in the rope. This means that we need to ‘de-rate’ the SWL of a rope by a factor depending upon what is called the PD ratio. This is the ratio of the diameter of the sheave wheel to the rope diameter, and the smaller the PD ratio the greater the de-rating factor that has to be applied to the SWL of the rope. It is beyond the scope of this brief article to delve too deeply into how the de-rating factor is determined, suffice to say that at a PD ratio of about 30, the de-rating factor is approximately 4%, but at a PD ratio of 16 it may be as much as 15%. This effect is very well illustrated if we look at the crown sheave on an Atlas Copco CS14 drill. The sheave wheel and wire rope combination yields a very high PD ratio and so a very low de-rating factor. This large diameter sheave wheel is not, therefore, cosmetic: it is there for a very particular reason. Wire ropes deteriorate over time due to the work that the rope does, but also due to the fact that ropes spool poorly on most drill rigs. As a rope deteriorates, its ability to safely lift a load will diminish and so the critical question becomes: at what point do we discard a wire rope? The decision is affected to some extent by the construction of the rope and also on its application. Many different industries that use wire ropes have developed their own discard standards but none of these are universally applicable to the drilling industry and so we must borrow from some of these. The following criteria are suggested as workable discard criteria for hoist ropes used in drilling applications:

If three or more broken wires are found in the close proximity to a rope termination;
If three or more broken wires are found in one strand;
If rope diameter anywhere is reduced to 90% of the nominal diameter; or
If a wave, birdcage, knot, loop, kink, localised flattening or any other defect is detected.

Colin Rice Exploration and Training, based in South Africa, is a provider of training courses for the exploration drilling industry

Published in the July/August 2017 edition of GeoDrilling International

Managing safety

Colin Rice, of Colin Rice Exploration & Training, describes a case study of drill site safety management in South Africa

Drill site safety has assumed an increasingly important role in South African exploration projects over the past eight years, and much of the increased focus on safety has been due to very onerous legislation that regulates operations. In South Africa, an exploration borehole is deemed to be a ‘mine’, and so all exploration drilling activities are regulated by the Mine Health and Safety Act. As the name suggests, the act was written to regulate mining activities and not drilling operations – in fact, the word ‘drilling’ appears only once. Nonetheless, all exploration activities must fully comply, and all persons involved in any exploration activity are subject to the very arduous requirements and the significant penalties that are prescribed in the act. Because there is no reference to drilling operations, mining companies have had to interpret the requirements of the act and then apply them to their respective exploration operations. Understandably, different mining companies interpret the requirements differently, and so several interpretations exist, and it is not uncommon that equipment deemed to be compliant at one mine is deemed to be non-compliant at another. This has caused confusion between contractors and their customers.

SOLVING A PROBLEM

Approximately six years ago, Colin Rice Exploration & Training was approached by a major mining company to conduct a safety audit on a 33-rig exploration drilling project. It involved rotary-percussion drilling, and both wireline and large-diameter conventional core drilling. Three contractors were awarded work on the project, and so the auditing project involved many different types of equipment operated by crews with a wide range of competencies. Most significantly, there were three companies with varying levels of understanding of the fundamentals of safety management and very different attitudes to drill-site safety. The contractor had very little idea of its legal responsibilities or of the consequences if it fell foul of the law. Previous safety audits had been done by safety officers from the mine, and often the officer reported issues that were frivolous, while serious safety issues were not identified. It was clear that the quality of the audit was directly related to the level of drilling experience of the safety officer, and so it was common that different officers would inspect the same operation and arrive at different findings. Consequently, conflicts grew more frequent – the contractor was viewed as ‘the problem’, and safety personnel appeared to be on a crusade to stop the contractor from working for whatever reason they could find. It was clear that the safety management system had to become more consistent and comprehensive, and so a project was started to develop a set of drill site safety standards that would cover all aspects of a drilling operation. From these standards, a set of standardised safety inspection checklists would be developed that would be used by both the mine personnel and the contractor to conduct inspections. The first step was the development of a drill-site safety standard, it had to:

interpret and include all legal requirements;
include all ‘best practice’ in cases where the legal requirement was insufficient;
include requirements for all drilling methods and techniques;
be easily understandable; and,
eliminate or reduce the level of subjectivity required in doing a safety inspection.

The development of the standard went through many iterations before it was considered complete, but at every stage it was shared with the contractors and the checklists were used in the safety inspection process. Since the contractor was included in the process, it took ownership and the development of the highest-quality standards became easy. In addition, because the contractor and safety officer used the same checklists to do their safety inspections, there were no surprises.

SAFETY STANDARDS

Drill site safety has four components, so the standards are developed in four sections:

Equipment: requirements for the drill rig, compressor, booster, water pump, mud-mixing facility, rod trucks and support trucks, welding machines, diesel and water bowsers.
Environment: general requirements while mobilising, drilling and during rehabilitation.
Personnel: requirements for crew and supervisor training and competence assessment.
Procedures: requirements for all routine and non-routine operations.

The inspection checklist asks a simple question directly related to each of the requirements in the standards document – the safety inspector merely has to tick a box: yes, no or not checked. The way in which the questions are framed eliminates subjectivity, and because every aspect of the operation is included in the checklist, the inspection is comprehensive.

Three separate checklists are used at different stages of the drilling operation. A pre-deployment inspection is done by a competent inspector, preferably at the contractor’s workshop, before the equipment leaves for site. In this way, any defects can be remedied in the workshop by qualified staff rather than at the mine. Once the drill and all ancillary equipment is on-site, set-up and ready, a pre-operation inspection is done. This will check issues that could not be inspected at the workshop; barricading, sump layout, lifting tackle and rod racking, for example, will all be checked. If all is in order, the inspector will authorise the contractor to start drilling. A periodic checklist is used on a weekly or biweekly basis and focuses on checking aspects of equipment that require regular maintenance and repair such as the core barrel, overshots, hoist cables, chuck jaws, quill rods, rotation-head guides, etc. This inspection also checks and verifies operating procedures. Initially the contractors pushed against the implementation of a safety standard. However, it did not take long for them to recognise that the process had many advantages. Firstly, it levelled the playing field – all contractors had to conform to the standard, and so pricing of contracts was much more comparable than was previously the case. Contractors also began to realise that improved levels of safety did not hinder productivity. Probably the greatest improvement was in the relationship between the contractor and the mining company; the contractor and the mine knew exactly what the requirements were and so there were no surprises when a safety inspection was done. Consequently, the contractor became a part of the solution to the problem.

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GeoDrilling International: Down to the wire