Dynamic sealing solutions prevent fugitive emissions

Paul Boughton

Control and management of fugitive emissions is becoming even more important for safety compliance, spawning a host of novel sealing solutions. Eugene McCarthy reports.

Marking another industry first for Flexitallic, the company says its Change gasket delivers a more dynamic seal with superior compression and recovery than any other gasket on the market.

Five years in the making, the Change gasket represents the development of a novel sealing construction which utilises a new advanced welding process to engineer a resilient metal-wound gasket.

Change can be supplied with Thermiculite, polytetrafluoroethylene (PTFE), or graphite filler combined with a wide variety of metals, making it suitable for an extensive range of applications, particularly heat exchangers and pressure vessels.

Exclusive to Flexitallic, Thermiculite gasket material can be utilised in systems that operate at extreme process temperatures, from cryogenics to temperatures in excess of 1000°C. Due to its insulating and fire-safe properties it is also highly effective at preventing corrosion.

The Change gasket comes hot on the heels of Flexitallic's Flange Rescue Gasket (FRG), which recently won the prestigious NACE 2013 corrosion innovation of the year award.

The company says that the FRG revolutionised the industry by being the first ever solution to seal damaged flanges without the need for replacement or machining.

Created in direct response to an industry-wide issue, the FRG reduces the lengthy and costly process of flange maintenance in corrosive environments. The gasket is fabricated from highly-compressible Sigma PTFE to ensure the FRG conforms to damaged flange surfaces to seal and prevent further deterioration.

The bright, easily identifiable FRG has a Fluoropolymer coated body which is corrosion resistant and features integral bolt holes for ease of installation and ensuring correct location. Superior mechanical integrity allows the use of the full range of torque - reducing the risk of operator error in order to meet stringent health and safety standards, not least those covering fugitive emissions.

Russ Currie, head of engineering at Flexitallic, said: "The Change gasket comes at an important time for the industry when further improvements in joint integrity are being sought and there is a renewed focus on prevention of hydrocarbon leaks. Change has out-performed all alternative gaskets tested to date, including our own gaskets, but we are continually looking to prove and improve our technology. We are engaging with companies that have troublesome applications to challenge Change, which will dramatically improve their performance."

Meanwhile Flowserve Corporation has signed a collaborative agreement with Advanced Diamond Technologies (ADT) to become the exclusive developer and supplier of diamond coated hard faces for its mechanical seals.

When applied to Flowserve base materials, the ultrananocrystalline structured diamond (UNCD) coating developed by ADT produces an exceptionally hard surface with significantly improved friction and wear characteristics. This is particularly beneficial in services requiring protection from slurry, dry running conditions and resistance to chemical corrosion.

The company has also completed a series of transactions related to its former Audco India joint venture with Larsen & Toubro (L&T).

As a result of these transactions, Flowserve obtains full ownership of the joint venture's Maraimalai Nagar (MMNagar) manufacturing facility in Chennai, India, and retains the key Serck AUDCO brand lubricated valve products and technology. L&T will retain the remaining AIL entity and its other operations. "We also plan to introduce new products for manufacture at the MMNagar facility, to fully maximise its capacity and promote greater localisation of our valve portfolio," said Tom Pajonas, senior vice president and chief operating officer, Flowserve.

Importance of material selection

When it comes to expansion joint design, material selection is critical. This is particularly true for the joints to flue gas desulphurisation (FGD) units. Although subjected to relatively low temperatures compared to other joints in the system, they are under constant chemical attack from the FGD process in a damp corrosive environment as cooling gases condense.

In addition to the chemical factors, these joints can be physically large - often up to 30metres in length - which brings its own problems in the physical handling requirements during installation.

As with all expansion joints, those for FGD units must also be designed and constructed to be sufficiently flexible to absorb movement yet strong enough to maintain seal integrity. James Walker Comflex expansion joints for this application utilise DuPont Viton B fluoroelastomer material of 6mm thickness, reinforced with a double layer of glass fabric.

All joints are fully vulcanised, rather than stitched, to create a fully welded joint. This combination provides both physical strength and resistance to chemical attack resulting in a robust joint with a long service warranty period far in excess of the performance life of other materials and joint designs for this application.

James Walker has also recently supplied over 4000 RotaBolt tension control fasteners for use on high integrity pipe work, vessels and large body flanges at Dow Corning's new chemical plant currently under construction in Jiangsu province, China.

The fasteners have been designed-in because of their successful track record in Dow Corning's flange management control systems at its plant in Barry, South Wales, where they have been in use for a number of years. Here the company has come to view RotaBolt fasteners as an important hardware component in its management of critical joints, as part of its commitment to high integrity systems. This has resulted in the fasteners being fitted on a number of pressure vessels and heat exchangers, in addition to some of the high integrity pipeline flanges.

The company has found the tactile tension monitoring system a major advantage, with an instant finger-test of the RotaCap on each fastener being all that is required to let the engineer know that the correct bolt load is being maintained.

Finally, several Garlock valve stem packing products were recently tested through ISO and API standard tests where they were proven to control and prevent leakage of volatile organic compounds (VOC).

Garlock value packing styles 1303 FEP, 212PULE and 9000EVSPPS were evaluated for emissions control based on fugitive emission standards ISOP15848P1 and API 622 2nd Edition. All three products demonstrated superior sealing performance and reliability in processing applications where VOCs are present, helping to ensure the safety of equipment operators and production crews (Fig.1).