Maintenance & Repair
- Published on Thursday, 13 March 2014 13:52
- Written by Greg Johnson
When watching complicated events unfold, it’s human nature to sit smugly back and think: I’m glad I don’t have to deal with that. For many of us in the repair community, this was the reaction when the Environmental Protection Agency (EPA) passed fugitive emissions regulations and valve manufacturers were forced to respond. Until now, we could nonchalantly stay uninvolved in the fracas.
However, the landscape is rapidly changing.
EPA uses consent decrees to “persuade” offending air polluters to clean up their acts. These decrees are a first step response to parties violating various clean air and clean water regulations. In the case of refineries and chemical plants, the decree usually directs the offender to take strong steps toward correcting problems. In the case of valves, that response may be ensuring that all valve purchases are bellows-seal types. More often, it is simply ensuring that all purchased valves meet low emissions (Low-E) requirements, usually with documented leakage rates that do not exceed 100 parts per million (ppm).
Valves used in places where emissions are a concern must be qualification tested and verified to meet the 100 ppm maximum leakage rate requirement. But the valve manufacturer has to step further out on a limb by guaranteeing this leakage limit for five years.
In the case of new valves, the testing process verifies that packing and packing systems are Low-E (less than 100 ppm). The process starts with a packing qualification tested in accordance with American Petroleum Institute (API) recommended practice RP622, Type Testing of Process Valve Packing for Fugitive Emissions. The test protocol is designed to qualify the packing by itself as compliant.
Following a successful API RP622 test, the packing can be inserted into a candidate valve and tested again. The standard for this second test will be the soon-to-be-published API 624, Type Testing of Rising Stem Valves Equipped with Graphite Packing for Fugitive Emissions. This document lists several sizes and pressure classes of valves to be tested so that packing and packing performance in the tested valves is verified as low emissions. One caveat of the standard is that the packing used in valves for the API 624 test must first be verified by an API RP622 test.
That’s fine for new valves, but what about repaired or post-OEM-manufactured modified valves? For many repaired valves, the design tolerances of the valve may be long gone. Therefore, it is now up to the repair facility to create a new Low-E packing system in concert with a low emissions packing manufacturer—and guarantee it for five years.
HOW TO RESPOND
Where do we start this process for repaired valves? We begin by working with a packing manufacturer that has qualified low fugitive emissions packings in their product lines. This will mean the manufacturer has successful RP 622 test data on the packing. The second step will be to assess quality systems and determine awareness of the dimensional tolerance requirements for these packings to work properly and that our equipment is capable of achieving the necessary tolerances and finish requirements.
Installation and effective use of Low-E packings require stem and stuffing box tolerances different from and tighter than those published in original valve design documents, such as API 600, Steel Gate Valves‒Flanged and Butt-welding Ends, Bolted Bonnets. This is because when they were originally drafted, the original packing gland and stuffing box design dimensions and tolerances of API 600, 602 and 603 were not designed with 100 ppm sealing performance in mind. The sealability of Low-E packing systems to meet maximum 100 ppm leakage demands much tighter tolerances.
Here are some of the components and dimensions critical for Low-E packing success:
- Stem run-out—the variation in stem diameter over a given length
- Stem straightness—the lack of linear dimensional stability
- Stem and stuffing box finish—the surface finish (roughness) of the stem and stuffing box wall. These can be either too smooth or too rough.
- Stuffing box inside diameter (ID)—the diameter of the inside of the stuffing box area that also coincides with the outside diameter (OD) of the packing
- Stem OD—this dimension coincides with the ID of the packing.
If an end-user or ultimate owner is faced with a consent decree, a five-year, 100 ppm guarantee will be required for repaired valves as well. This guarantee will actually be written by the packing manufacturer, but only if there is traceability that individual tolerance requirements have been met and that the packing has been installed in accordance with detailed installation procedures. These procedures may include very specific torques and/or valve cycling requirements.
Currently, no production testing standard exists for Low-E verification. Hopefully, API or some other standards organization will develop a procedure and acceptance criteria for such a test. One factor that makes such testing difficult is that both the API RP622 and 624 documents use methane as the testing media. For safety reasons, a production test would almost have to use an inert gas such as helium. As of now, there is no correlation between helium and methane leakage rates.
Unfortunately, there will be an added cost for Low-E certified repaired valves. However, if the service is performed correctly in a cost-productive manner, the opportunity and potential profit will outweigh those costs.