Published in September 2008 Australian Longwall Magazine

Hydraulic hose assembly failures are increasing on aging longwall supports leading to an increased risk of injury and production down time. With little in place to help industry plan for or prevent hose failures, researchers at Monash University are investigating the factors contributing to premature hose failures.

A recent survey out of the United States has shown more than 60% of longwall operations with shields in service for 4-6 years have developed significant problems.

Combine this with an increasing rate of injury from hydraulic hose failures and there is impetus to find how to better manage hose systems underground.

With between 10,000 to 30,000 hoses found on a typical longwall face, and with no hose management plan found throughout Monash University surveyed longwall sites, some mines are experiencing unpredictable and dangerous longwall failures.

Besides a safety issues, these breakdowns also impact production. With this in mind Monash embarked on an Australian Coal Research Program-funded project to establish hose failure patterns.

Monash University Maintenance Technology Institute researcher Henry Bartosiewicz, who is leading the study, said the project was looking to give clarity around the life of a hose, how and why hoses fail, and what can be done to prevent them from failing.

“Preliminary focus of the investigation is to minimise the potential for injury,” Bartosiewicz told Australian Longwall Magazine.

“The objective of this project is to identify possible improvements in longwall hydraulic system and hose assembly selection, management, operation and maintenance to reduce the risk of injuries and to maximise effective hose assembly service life.”

Statistics from Coal Services showed injuries from hydraulic fluid and hoses were on the rise from 37 in 2006-2007 to 60 in 2007-2008.

Bartosiewicz said motion and control technology firm Parker-Hannifen reported in a Longwall Hydraulic Hazards Workshop last year that there were 255 longwall hydraulic incidents over the past eight years with hose and fittings failures accounting for 159 injuries.

In a bid to improve safety underground and identify the causes of hose failures Monash consulted with industry and surveyed its concerns.

“Our work program set through talking with the mining industry as well as the longwall, hose and pump manufacturers,” Bartosiewicz said.

So far the researchers have collected and analysed data from failed hose assemblies, minesite hose failure records, longwall original equipment manufacturers, hose suppliers and interviewed minesite personnel from 13 sites.

So what is happening underground that is causing hose failures?

Examining the failed hoses Bartosiewicz found mechanical damage, corrosion of wire, burst hoses, and degradation of the hose cover. Mechanical damage included abrasion and impact kinks.

Corrosion was found in wire reinforcing strands, staples, ferrules and couplings with some hoses showing thinning of the third and fourth braid layers due to corrosion.

There was a loss of tensile strength and adhesion to the reinforced wire due to the degradation of the rubber/polymer hose cover.

In a move to manage the risks associated with hydraulic hose failures, the New South Wales Department of Primary Industries developed the Mechanical Design Guidelines (MDG) 41 for fluid power safety systems in mines.

The guideline pushes mines into setting up high-pressure fluid management systems. The move has been embraced by industry.

Although Bartosiewicz found all sites had taken some steps to comply with MDG41, his research showed none of the sites had a clear action plan to meet compliance and needed more help.

Throughout the surveys all sites expressed concerns over the potential difference in interpretations in the MDG 41 and most sites said they did not expect full compliance with the guidelines for another two years. Many sites doubted they would ever comply due to budgetary and resources constraints, Bartosiewicz said.

So what are sites doing to minimise hose failures?

Research found most sites had introduced hose sleeves to minimise the risk of hydraulic injection.

However, the study found most sites were unable to identify where their hose failures were taking place and with what type of hoses.

Through the experience of the minesite workers some common hose failures were identified including:

• DA ram and base lift hoses.
• Lower hoses.
• Leg set hoses.
• Side shield and flipper hoses.
• Hoses routed across the lemniscate linkages.

The key drivers for hose replacement were mechanical damage, corrosion, installation and aging. The number of hoses replaced a year varied between sites.

Some sites had hoses in service for more than 12 years in areas free of wear, corrosion, bending. But hoses in shield tunnel areas tended to last only about 6-24 months with the average hose service life in other areas between 3-6 years.

The service life of hoses for sites with severe corrosive environments was less than two years.

The studies found most sites do not track where and when individual hoses were installed and the common hose assembly lifecycle management was the re-hosing of certain number of supports per relocation or per maintenance day.

The documenting of hose failures was better in some mines than others, however few sites were capturing enough data, Bartosiewicz said. The detail and format of information being captured varied significantly. Bartosiewicz found only one site could demonstrate the analysis of captured data in order to drive improvements and safety with three months of data.

Through his survey data, Bartosiewicz found the following was needed:

• A framework on effective hose management systems.
• There was a lack of guidelines on the selection and application of hose protective sleeving, spiral wraps, hard barriers and hose restrains including the evaluation of the effectiveness of different sleeve/spiral wraps and hard barrier arrangements to reduce potential for fluid injection, burst hose injury and to minimise abrasion and impact damage.
• Design modifications to minimise hose abrasion.
• A guideline on the selection and use of staples in longwalls systems.
• Minimum performance requirements must be established for hoses and hose fittings for a range of operating environments in Australian coal mines. This could include benchmark testing of hoses provided by hose suppliers including abrasion resistance, impact damage and corrosion resistance of reinforced wire.
• Clear guidelines on how to specify and select hoses for different services and operating environments.
• Hose assembly specifications for new longwall systems.
• A training and hazard program for longwall trades which could be audited.
• Clearer identification of high, medium and low-pressure fluid lines.

The study is hoping to provide longwall industry with more clarity and structure on how to manage their hoses and hydraulic issues. A hose management plan is expected to be completed by May next year.

The second part of the project, for which Monash is applying for an extension from ACARP, will look more closely at the hose design and what type of prequalification testing is required. This in turn would further reduce the risk of hose failures and injuries.