Are you having problems with sealing your tank car manways? Are you worried about Non Accident Releases (NARs)? Are you seeing inconsistencies on how your manway gaskets are installed?
Despite crude oil being below $50 a barrel and the DOT’s list of retro-fits and new build guidelines, tank car shipments continue to grow. According to Railinc’s Railcar Review 2015, tank cars now represent 19% of the total rail fleet and 24% of the revenue earning fleet, growing by 9.4% in 2014 to a total of 371,000 cars.
In the first quarter of 2015, the AAR reported 248,336 carloads of crude, ethanol and other flammable liquids (82,508 unique cars). Approximately half of those carloads were shipped on DOT-111 tank cars. Absent from the DOT’s ‘Final Rule’ on tank car safety, is the omission of steps to resolve NARs, which saw a 19% increase in 2014.
Top issues for manway gasket failures
Numerous gasket suppliers have marketed new designs and materials to help improve manway sealing. Today some gaskets are accompanied with very detailed paperwork and packaging to convince shippers that their gasket will solve the unrelenting issue of NARs. Regardless of which gasket is being used, the same issues always exist:
- Manway damage (stripped bolts)
The physics of sealing
Elastomers (rubber) suffer from compression set or how much an elastomer is permanently deformed after being compressed. Zero compression set means the elastomer completely returns to its original shape whereas, 100% compression set, means the elastomer remained in the deformed position and did not recover at all. It is an elastomer’s ability to ‘bounce back’ that makes it reusable.
In the case of PTFE gaskets (commonly known by its brand name – Teflon™ or Garlock®), while they have excellent chemical resistance, they suffer from cold-flow (sometimes referred to as creep), which is the tendency of a solid material to permanently deform under the influence of force. This lack of memory renders any PTFE a single use sealing material.
Why shippers struggle
Due to compression set or creep, bolts will lose torque and loosen and therefore require additional torquing. The use of impact wrenches over-compress elastomeric gaskets, far exceeding their stress / strain limits and causing them to split or crack (25% compression is the ideal amount of pressure required to achieve optimal sealing). In the case of PTFE, excess over-torquing will quickly damage the fittings as well as require additional re-torquing. This is why most gaskets cannot be guaranteed re-usable.
An engineered solution
Sealing and maintaining bolt torque is not a unique challenge for tank cars. Using a technology similar to that of automotive gaskets, Parker Hannifin has developed the Sure Torque gasket. Its compression controlling, stainless steel insert completely eliminates all issues related to compression set and creep.It is a universal design that fits all nozzle and lid designs.
- This is a reusable gasket (guaranteed by Parker)
- This is a gasket that maintains bolt torque
- This is a gasket that does not require re-torquing
- This is a gasket that can’t fall into the manway
With great care and effort, achieving an effective seal is attainable with existing gaskets. However, the risk and cost of doing so remains unacceptably high. The costs of failing to achieve that seal are even greater when considering potential fines and environmental clean-up costs. For some shippers, it may mean losing the contents of that tank car in the event of contamination.
The Parker Sure Torque Manway Gasket incorporates an integrated stainless steel ring that specifically resolves the four leading issues that cause manway NARs. It is the only gasket that can be reused, that has to be torqued once and greatly simplifies installation and maintenance procedures.
To learn more, view our video on the Parker Sure Torque Manway Nozzle Gasket below.