Maintenance: the end of repairs?

A stitch in time saves nine, so the old saying goes. Yet strangely, for a long time this piece of old wives’ wisdom fell on deaf ears when it came to maintaining pumps and valves.

However, over the past decade or so, asset-management-related legislation and regulations in various process sectors have combined with plant owners’ increasing awareness of maintenance costs, plus newly available and affordable technology, to create a perfect storm for encouraging a more pro-active approach to maintenance.

In the water industry, for example, the Water Industry Mechanical and Electrical Specifications (WIMES) series of standards developed by the Pump Centre in partnership with water utilities has helped shift focus on to considering whole life costs of a pump, says Schneider Electric water solutions architect Richard Luke.

“Historically pumps have been bought on the capital purchase costs but, thanks to WIMES, plant owners are starting to understand the true cost of a pump,” says Luke.

“The focus on the capital cost of a pump wasn’t giving good value, and there has been a shift away from that to looking at whole life cost. Maintenance used to be based on so many hours of running, and then maintain the pump whether it needed it or not. Now you can use sensors to monitor things like temperature, and at Schneider we have software that will look at the harmonics caused by the pump drive: if there is any change in the usual pattern, this suggests that there is a problem with the drive or the pump itself.”

Maintenance’s status in the water industry is set to rise rapidly over the next few years.

For the current regulatory period, which runs from 2015 to 2020 and is called AMP6, water companies are being asked by industry regulator Ofwat to focus their efforts on a concept called ‘Totex’.

Put simply, Totex stands for total expenditure, and requires water companies to shift their investment outlay from initial capital costs to total expenditure during the life of an asset.

As part of its focus on Totex, Ofwat is calling on water companies to consider innovative technologies that can make their assets both more efficient and last longer – including condition monitoring technology.

Retiring ‘repairs’

It is not just in the water sector, and pumps are not the only components, where the financial advantage of maintenance over repair is increasingly important to plant operators.

“‘Valve management’ is very much the war cry these days, rather than simply talking about valve repair,” says British Valve and Actuator Association (BVAA) director Rob Bartlett.

“There are massive losses to be made by something going wrong at an awkward time, so it’s all about managing valve outages and predictive/preventative maintenance. For example, offshore [oil & gas fields] have scheduled shutdown periods for maintenance. If you have a valve that is coming to the end of its optimum performance, or could potentially fail before the next available shutdown, you want to deal with it during that period, rather than having it fail later and cause a costly emergency shutdown.”

Valve failures in the oil & gas sector can be extremely costly – not only from the lost production while a field is down, but also just the cost of the components themselves.

Modern valves in the sector are being designed to handle pressures of up to 15,000psi, measure up to 6m long by 3m high, and cost millions of pounds.

In addition to cost concerns, another key driver for a proactive approach to maintenance has been industry regulations, particularly as far as the North Sea is concerned.

As a result of its Ageing and Life Extension Inspection Programme (KP4), which ran from 2010 to 2013, the Health and Safety Executive (HSE) issued a number of recommendations relating to the asset integrity of ageing offshore platforms – all pointing to more proactive, risk-based approach as the way to keep ageing platforms free from failure.

The HSE’s KP4 report points out that equipment inspections were “generally time-based using original equipment manufacturers’ recommendations and historic failure patterns”.

“This may have been largely successful, but it is not in keeping with a risk-based assessment approach, and does not anticipate the changes of fluid properties as reservoirs are depleted, and the consequences of those changes on equipment performance and reliability,” says the report.

“The industry is missing an opportunity to improve upon both safety and reliability management.”

Spending cuts

However, given the current low oil prices, some question whether oil & gas operators are taking the HSE’s advice.

Alun Jenkins, general manager at valve service provider Denholm Valvecare, says that while his company’s inspections of pressure safety release valves continue unaffected by the low oil price, thanks to insurance and HSE legislation demanding regular testing of these critical components, in other areas, such as inspections of control valves, operators have slashed spending.

“Like any valve company at the moment we are suffering, driven by the low oil price,” says Jenkins.

“It is more and more difficult to get people to spend any money. Turnarounds (TARS) are being shelved or backburnered, because people aren’t producing as much. You would think they would take the downtime as an opportunity to carry out assessments and maintenance and be a bit more proactive, but we are not seeing that. The downturn has not led to an upturn in maintenance.” However, others have found ways around oil & gas operators’ reluctance to spend by demonstrating the significant cost savings that can be achieved through condition monitoring and predictive maintenance.

Driven by a growing appetite among its customers for greater information about the condition of their assets, valve services company Score Group in 2012 launched a dedicated monitoring division called Score Diagnostics.

Score Diagnostics specialises in valve leak detection based on acoustic emissions with equipment sold under the Midas brand that ranges from handheld leak meters through to fully integrated valve condition monitoring equipment.

Score Diagnostics sales and marketing manager Dave Anderson says that despite price pressures, HSE regulations such as those resulting from KP4 have combined with new standards around asset management such as ISO55000 to force operators to look at better ways of maintaining their oil & gas facilities.

“There’s an increasing understanding, and increased appetite for the services we provide, and the cost savings with a low oil price become highly attractive,” says Anderson.

“However, the flip side of that is that the interest is coming at a time when there’s very little capital to invest.”

Anderson points out that the company’s entry level handheld device – the Midas Meter – represents a very small investment, but beyond that his company has been able to introduce innovative ways of working that enable operators to realise the significant cost savings that can be achieved through condition monitoring.

“Operators may not have any cash available for capital expenditure (capex), but they do still have money for operational expenditure (opex),” says Anderson.

“With one company we used that opex budget to carry out a pre-shutdown survey. Carrying out condition monitoring in advance of the shutdown means that rather than following manufacturers’ guidelines [for maintenance periods], maintenance was only carried out on those valves that genuinely needed attention. We were able to demonstrate a cost saving of £340,000 from a survey that cost just £5,000.

“It’s not game-over just because nobody has capex; you just have to find a different way of working.”

Acoustic testing for valve leakage

Traditional methods of inspecting the condition of valves require the valve – and often the whole plant – to be taken out of service so the valve can be assessed.

However, when a valve leaks it generates turbulence and noise that can be detected. The fluctuating pressure field generated by the turbulence from a leak creates what is known as an Acoustic Emission (AE) signal. This signal is then transmitted through the fluid and valve wall and can then be detected on the outside of the valve.

The AE signals are generated across a wide range of frequencies, but using very high frequency detectors (60 kHz to 600 kHz) the low frequency, audible background noise is filtered out.

Therefore, the technique can be used in noisy operational plant environments, for example valves adjacent to compressors and pumps.

Score Diagnostic’s survey technique using its Midas Meter requires the test valve to be closed, with a known differential applied across the valve.

The pressure difference ideally should be greater than 10 bar. Leakages can be detected at lower pressures, but with a loss of sensitivity.

The sensor is then held in contact with the valve on a flat clean surface using an acoustic couplant such as silicone grease.

Several points on the valve body are measured, and the highest stable reading is then recorded. Background readings on the up and downstream pipework are then taken to ensure that it is the valve that is the source of the leakage noise, and not an adjacent valve.

As measurements are taken in the high frequency range, the recorded AE signal will weaken rapidly the further it gets from its source. This enables the source of the AE signal to be easily located.

This becomes highly valuable when dealing with closely spaced valves on manifolds where there are many potential leak paths.