Although every crane is designed with a certain duty cycle in mind, the situation is more complicated than first meets the eye. The problem is the large mix of legacy and modern cranes in use today, which were constructed to different build principles. Legacy cranes were manufactured using the maximum stress principle: for a given load there is a maximum stress threshold. This conservative approach means that many older cranes last for a very long time, sometimes beyond 100 years. In contrast, modern crane production uses the limit state principle, where cranes are built on the limits of what they can achieve in service.
“Herein lies the problem, as many in the industry are used to cranes that simply last and last,” says Ben Dobbs, head of technical services at the Lifting Equipment Engineers Association (LEEA). “Instead, modern cranes only endure for a given number of lift cycles, after which they need major overhaul, repair or even replacement in some cases.”
DESIGN LIFE
Crane life is measured in different ways. Structures, for example, use up design life with every lift/stress cycle, whereas mechanisms such as hoists and motors (machinery) consume design life based on running hours, whether under load or not.
“These factors determine a crane’s fatigue life,” explains Dobbs. “They are influential because the time taken for a crack on a structure to move from ‘detectable’ to ‘failure’ is relatively long, whereas cracks in mechanisms can deteriorate very quickly, often quicker than the annual thorough inspection under LOLER regulations. For this reason, it’s good practice to evaluate the design working period of the crane as a supplement to LOLER [Lifting Operations and Lifting Equipment Regulations] and PUWER [Provision and Use of Work Equipment Regulations] requirements.”
Many modern cranes feature integral condition monitoring to track the number of completed cycles. The system will measure the magnitude and frequency of lifts, using the data to calculate remaining crane life. Some condition monitoring systems even shut the crane down when it reaches its specified number of duty cycles.
Says Dobbs: “When talking about the duty cycles of modern cranes, the manufacturer will set out how many lifts can be performed. This will be a finite number – such as 10,000 – after which the crane will require overhauling or replacing, whether it has a defect or not. Many crane manufacturers therefore offer an overhaul kit. When the crane reaches its duty cycle limit, some companies will not even inspect the crane, but simply replace the critical components with those in the kit.”
BIG SHIFT
According to Dobbs, the growing importance of design life is “the big shift in the crane world right now”. A crane might carry a five-year lifespan, for example, but it will also have a finite number of lift cycles. If used more frequently than intended, the five-year lifespan may become two years, for instance. Similarly, if used less frequently, crane life could expand.
“We see it commonly in factories where a crane was installed to serve a particular production line, but the company’s volumes have increased and they are still using the same equipment,” he says. “Ultimately, it’s up to the owner of the equipment to fully understand crane duty and their responsibilities in terms of ongoing safety. They must ensure that it remains fit for purpose, with regular inspections and maintenance, while also looking at remaining crane life.” He points out that standard ISO 12482 can help do that on legacy cranes without condition monitoring.
CRITICAL PARTS
As well as a thorough examination every 12 months under LOLER, interim inspections (depending on use) are required in order to comply with PUWER. These inspections include looking at critical parts to control the risks associated with age. Typical age-related component failures in cranes include those associated with hoists, hooks, wire ropes, sheaves, drums and beams. Weld failures and metal fatigue are not uncommon.
“We’re increasingly finding that the thorough examinations are not as thorough as they ought to be,” states Dobbs. “For instance, no one seems to strip down an entire hoist mechanism due to the time and cost involved, so we know there are critical components not getting checked. That’s why it’s important to supplement the legislative requirements with design life analysis.”
As a trade association, LEEA trains people to give them the skills required to competently inspect particular items of lifting machinery or accessories.
“However, competency is a lot more than just education; it’s about practicalities, understanding and experience,” concludes Dobbs. “It’s ultimately up to employers, who are responsible for fulfilling all of the obligations imposed by LOLER and PUWER, to decide if their individuals are competent to perform crane inspections. They can of course outsource this activity to a third party, but doing so does not absolve them of responsibility, as they must still ensure that the organisation or persons employed have the necessary knowledge, experience, training, skill and ability to perform the required task.”
BOX: COMMON LAW DUTY OF CARE
Lifting operations are inherently dangerous due to the need to overcome gravity with every single lift. So on 7 May 2007, Mike Ponsonby, as an appointed person and director of Michael J Ponsonby Ltd, started researching all crane and lifting Incidents worldwide. Today, he has amassed 1,132 incidents to date, causing a total of 614 fatalities.
“During this 15-year period, it’s become clear to me that we are witnessing many of the same mistakes over and over again,” he says. “For example, there have been 565 examples of poor outrigger set-up.”
Primary legislation in UK is the Health and Safety at Work Act 1974, with the relevant secondary legislation being LOLER 1998. “These legislative obligations mean that in the event of a fatal Incident, UK employers may be held liable by the Crown Prosecution Service for the criminal charge of corporate manslaughter,” says Ponsonby. “So the only way that directors can protect their business from this major risk is by compliance with all of the relevant legislative and common law obligations, starting with better training, instruction and supervision.”
UK employers are under a common law duty of care to all employees and other members of the public affected by their acts, he says. “This duty has many implications, one of which is the legislative duty to undertake thorough examinations of all cranes and lifting accessories, in line with Regulation 9 of LOLER.
“All maintenance and safety inspections must be done in line with the manufacturer’s recommendations, irrespective of the crane’s age, with all wear components like brake pads, bands and shoes replaced before they get to the lowest level.”
A thorough examination is required every 12 months, although if the crane lifts a man basket containing a person (even once a year) then a thorough examination is necessary every six months. Lifting accessories like slings, chain brothers and shackles must undergo inspection before use.