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Calculating the true costs of seal failure

01 September 2014

The performance and reliability of ‘O’ ring sealing systems can have a huge impact on overall plant costs, particularly if the sealed fluids are aggressive, or pose a danger to personnel and the environment in the event of process fluid leakage due to seal failures.

Conventional elastomer seals which have proved to last the lifetime of process equipment, or provide leak-free operation between programmed maintenance break-outs may have established their suitability.

However, sealing products that regularly fail, necessitating equipment strip-downs, loss of productivity and costly clean-ups, should have the costs associated with these remedial procedures factored in when considering the overall costs of seal replacements.

The DuPont Kalrez range of perfluoroelastomer seals, available in the UK from Dichtomatik, can show worthwhile long-term savings by extending mean times between failures (MTBF) and so minimising any associated labour and downtime losses.

It is important that the true cost of system failures include all the additional associated costs involved with equipment dismantling and re-assembly, downtime and loss of production. This should also include possible clean-up where aggressive chemicals are involved as well as the straightforward costs involved in replacing the sealing seals.

Case studies
One particular application in which Dichtomatik was involved, had hitherto made use of dynamic PTFE ‘O’ rings in the production of biotechnology products, including solvents, surfactants and concentrated herbicides at temperatures from 10°C to 45°C and pressures from 1.5 to 3.5bar. In this case, an average seal lifetime of just one working day was extended to an equivalent lifetime of 2 months MTBF when the PTFE seals were replaced with Kalrez Spectrum 6375 perfluoroelastomer ‘O’ rings.

In even more dramatic circumstances, fluoroelastomer (FEP/FKM) piston rod seals with a typical lifetime of eight hours operation were substantially extended to between eight and twelve months between replacements when high performance Kalrez parts were substituted.

In a further case study, shaft seals utilised in pumps for pharmaceutical, chemical and petrochemical processing applications, which also included handling concentrated sulphuric acid, were also recorded. For safety reasons, seals were replaced at regular scheduled times, based upon the history of seal failures which occurred after a maximum service life of only two months.

Following the replacement of the existing ‘O’ ring seals with Kalrez Spectrum 6375 products, no seal replacements or associated servicing costs were experienced over the following 20 months. Fitting the Kalrez products provided the necessary higher resistance to chemicals and increased operating uptime, resulting in substantial savings thanks to the reduction in costly downtime.

Case studies where cartridge type mechanical shaft seals are utilised within chemical processing plants also indicate that, overall plant savings are still achievable with the introduction of Kalrez products as replacements for non-FFKM ‘O’ rings.

Even when single mechanical seals incorporate up to seven ‘O’ rings, with up to 20 production breakdowns per year, then an overall 4 percent savings per annum can still be achieved against the total system costs. These include all seal replacements with Kalrez products, plus downtime and other associated costs. Where 30 production breakdowns through seal failures occur, then the overall savings per annum increases to a healthy 27 percent.

Within the same plant environment, where single non-FFKM ‘O’ ring seals are incorporated in couplings, replacements with Kalrez products can double the MTBF times from one and a half years to three years without leakage. This can achieve overall system cost savings of 89 percent – and up to 98 percent where MTBF times are increased from six months to three years.

Kalrez perfluoroelastomer sealing parts have an established value-in-use, including resistance to some 1,800 chemicals and solvents. ISO 3384 tests under harsh and aggressive conditions also indicate lengthier retention of sealing forces.

Low compression set is also achieved with Kalrez Spectrum 7075 which recovers better under compression than many other perfluoroelastomers, so maintaining the shape under prolonged stress. Elasticity and recovery properties are high even after long-term exposure to temperatures as high as 327°C.

DuPont Kalrez products are supported with a worldwide network of authorised distributors including global technical support and testing. Customer tailored selections are available with standard ‘O’ rings available in AS-568 and JIS sizes as well as customised ‘O’ rings in various cross sections and diameters.

These products are complemented by customised valve seats, diaphragms, gaskets, packer seals, T seals, column fittings, custom shapes and the Kalrez KVSP valve stem packing system.

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