‘O’ ring sealing system reduces pump operating costs

The performance and reliability of ‘O’ ring sealing systems within process plants can prove to be critical when examining overall plant costs. This becomes evident where the process fluids are aggressive, or otherwise dangerous to personnel safety, and environmental concerns become involved 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 exhibit regular failures, necessitating costly equipment stripdowns, loss of productivity, together with leakage and clean-up procedures should have the costs for the above procedures factored in when considering the overall costs of seal replacements.

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 products (typically ‘O’ rings).

Case studies are available for examination  which include the use of dynamic ‘O’ rings of PTFE (Polytetra-fluoroethylene) for the production of biotechnology products including solvents, surfactants and concentrated herbicides at temperatures from +10 to +45°C and pressures of 1.5-3.5 bar Eff. An average seal lifetime of one working day, was extended to an equivalent lifetime of two 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 8 hours operation were substantially extended to 8-12 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 level to chemicals, increased operating uptime and resulted in overall savings through the reduction of costly downtimes.

Case studies where cartridge type mechanical shaft seals are utilised within chemical processing plants also indicate that, overall plant savings can still be achieved by the introduction of Kalrez products to replace non-FFKM ‘O’ rings. Even when single mechanical seals incorporate up to 7 ‘O’ rings, with up to 20 production breakdowns per year, then an overall 4% savings per annum can still be achieved against the total system costs, which include all seal replacements with Kalrez products, plus downtime costs etc. Where 30 production breakdowns through seal failures occur, then the overall savings per annum increases to a healthy 27%.

Within the same plant environment, where single non-FFKM ‘O’ ring seals are incorporated in couplings, then replacements with Kalrez products can double the MTBF times from 1.5 to 3 years without leakage. This can achieve overall system cost savings of 89%. These can even be increased to 98% savings where MTBF times are increased from 6 months to 3 years.

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 up to 327°C.

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