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SATURDAY ENGINEERING BRUNCH 2 - Science/Technology - Nairaland

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SATURDAY Brunch:zone Classification Oil And Gas Industry. (2) (3) (4)

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SATURDAY ENGINEERING BRUNCH 2 by Nobody: 1:09pm On Aug 23, 2015
Welcome to part 2 of the Saturday Engineering Brunch.
I trust your week has been nothing but delight.
I aslo do hope you have had a wonderful time savouring the engineering dishes served in ENGINEERING BRUNCH 1 ON Oil and Gas Zone Classification.

Todays menu is as usual a three course meal.


With a starter meal,My Appetizer : PROCESS SAFETY BEACON, OPERATIONAL READINESS

MAIN DISH: CONSIDER ZONE 0 VERTICAL PUMPS FOR SLOP PITS


CONSIDER ZONE 0 VERTICAL PUMPS FOR SLOP PITS
Over the past several decades, a leading overseas HPI corporation experienced a disturbing number of explosions in its belowground hydrocarbon sump pits.
Over the past several decades, a leading overseas hydrocarbon processing industry (HPI) corporation experienced a disturbing number of explosions in its belowground hydrocarbon sump pits.
Gravity-fed oily water “slop” and spillage from surrounding process facilities feed into these concrete pits; they typically range from 15 ft to 35 ft in depth. An unpredictable product slate causes the sumps to be exposed to two highly undesirable conditions: a volatile hydrocarbon mixed with air, and an enclosed space.
It can take only a temperature excursion to spark a blaze. Equally unpredictable and random, this high temperature can be caused by a spark or through rubbing contact of metals, with resulting temperatures above 600°F.
At the overseas corporation’s facilities, the recorded ignition events had their origins in external triggers—lightning, nearby welding, etc. Also, at other times, internal causes were responsible. Both small and large components were known to occasionally fail in American Petroleum Institue-compliant vertical sump pumps of various designs and types.
Relevant input from a senior corporate reliability engineer at that corporation is hereby gratefully acknowledged. The engineer asked for comment on similar occurrences at other facilities and an outline for the steps needed to address this important safety concern. In the past six years, the staff at his corporate offices had examined and researched several risk-abatement solutions. Management then agreed to proactively pursue a set of mandatory facility improvements that called for or included :
1. Maximized use of aboveground, self-priming, motor-driven centrifugal pumps on new and existing installations as a mandatory design requirement. Such pumps must be approved by the manufacturer for hydrocarbon liquid operation and include liquid-filled mechanical seals, full stainless steel construction and temperature sensors.
2. Utilization of carefully designed vertical centrifugal pumps for pits where greater depth makes aboveground horizontal pumps impractical.
3. Consideration of submersible electric-powered pumps as unacceptable due to the possibility of electrical ignition from damaged cables or dry running. However, ATEX-certified hydraulic-powered submersible sump pumps with an external drive source for smaller pits are considered acceptable.
4. Installation of redundant radar-type liquid level gauges on all sump pits. (These gauges have the highest proven reliability in sump service.)
5. Reduction of the possibility of hydrocarbon entry into oily-water sumps (“slop pits”).
6. Requiring pressure switches or flowmeters with time delay on the sump pump discharge piping, which will shut down equipment in the case of no-flow events.
The corporate reliability engineer mentioned that, notwithstanding point No. 5, the refinery process units would most likely continue to route every conceivable type of runoff to the sump pits. He considered it virtually impossible to fully control such drainage. Accordingly, he suggested that the importance of the issue be highlighted to HPI plant safety worldwide.
He has been uncomfortable with belowground pits in hydrocarbon processing plants. Early in his 30-year career, he realized that applicable loss-prevention standards disallow below-level installations, although sump pits with hydrocarbons abounded both then and now. He reaffirmed that potential pump-related ignition sources included defective pumps, dry running pumps and faulty cables on submersible pumps.

Building sump pumps for Zone 0
Explosions in oily-water sump pits are primarily a function of the concentration of flammable or explosive mixtures in these belowground level locations. Concentrations differ from plant to plant and from unit to unit. Moreover, concentrations vary greatly with operating practices. What is an intolerable spill to one group or individual may be brushed off as a negligible trickle by another group or person.
The safest approach eliminates the element of human judgment during design; this approach also greatly reduces human-error risk over a plant’s lifetime. Serious advocacy and implementation of best available technology are included in the safest approach. Safe solutions should cover situations where unexpected hydrocarbon concentrations exist and where there is no time for operator intervention.
Zone 0-compliant pumps (Table 1) represent an experience-based option. Equipment built for this zone should reflect best available technology; the equipment must be exceedingly well protected against becoming an ignition source. Well-designed vertical pumps are suitable for belowground installation.


Pumps classified as suitable for Zone 0
Many vertical sump pumps are single-stage designs. They incorporate an end-suction “back-pullout” casing, where the hydraulic end is mounted below the liquid level. The impeller is connected to a motor, usually mounted above the sole plate on an adaptor stand by means of an extended shaft. This shaft is housed and supported in a rigid tubular intermediate pipe (Fig. 1).

Fig.1. Zone 0-rated, vertical-
enclosed, shaft-driven sump
pumps are certified for
explosion-proof areas.
Reliability-focused users
mandate meeting Zone 0
classification and conformance
with relevant EN 50014
regulations. Image source:
Egger Pumps.

The motor stand is manufactured with register-style (“rabetted”) engagement fits to ensure alignment concentricity of both motor and pump shaft ends. A non-sparking flexible coupling can be accessed from opposite sides, and protective guards are provided. Flange-mounted motors can be either metric or National Electrical Manufacturers Association frames.
Sump pump designs that tolerate a certain amount of solids typically incorporate fully recessed vortex flow impellers (Fig. 2) or semi-open impellers. These impellers likely have rear-mounting shrouds that incorporate integrally cast back balancing vanes. Designs of this type are especially suitable for moving free-flowing slurries and sludge.


Fig.2.Recessed impeller and back pullout
are typical features of Zone 0 pumps.
Image source: Egger Pumps.

Although the impeller design is capable of handling solids up to the diameter of the discharge port, a suction strainer—fitted to protect the spark arrestor—limits the practical solid size. Nevertheless, this impeller’s construction and geometric layout place mechanical and process safety ahead of power efficiency. A well-designed Zone 0 pump can stand an occasional unforeseen or difficult service condition. It may cost more than the lowest as-purchased alternative, but it is worth much more than the cheapest similar pump available.
The unique feature of one such recessed impeller pump is found in the design of the actual pump case. Case internals are cast or machined with a helical contour that contributes to improved hydraulic efficiency without impeding free passage. For ease of maintenance, all machined mating faces incorporate locating registers. Thus, when the pump is reassembled, it is totally self-aligning. The impeller is then keyed to the shaft and locked in position with an impeller screw and tab washer.
The preferred pump usually incorporates a large sole plate or pit cover (Fig. 1), which makes it possible to mount the unit on top of a tank or on the beams bridging the sump pit (Fig. 3). The discharge pipe passes through the sole plate and is held in position by means of a weld neck flange bolted to the sole plate. The manufacturer provides a floating discharge flange that facilitates and simplifies matching the pump discharge pipe to the owner-operator’s discharge pipe system.


Fig.3. Zone0 pump and important
auxiliaries. Image source: Egger Pumps

Applicable regulations may require the Zone 0 pump to be fitted with a minimum flow bypass. This bypass eliminates the dangers of blocked discharge and vaporization of fluid. The bypass pipe is connected from the discharge pipe and directed through the sole plate back into the tank. Two minimum-liquid-level probes are mounted in the sole plate; one is for monitoring the liquid level in the tank, and the other is for detecting the liquid level in the column pipe. Each probe is fitted in an explosion-proof enclosure.
A spark arrestor is provided on the discharge pipe near the cover plate; ball valves are typically fitted on either side of the arrestor (Fig. 3). One particular design is often sold with a single mechanical shaft seal (conforming to DIN 24960 dimensions) behind the impeller. The seal is mounted on a replaceable shaft sleeve. A bottom journal bearing is provided and mounted on a separate replaceable shaft sleeve.
Other modern sealing solutions are available and deserve consideration. As an example, a respected and innovative mechanical seal manufacturer engineered the Cartridge API (CAPI) range seals shown in Fig. 4. This CAPI range of API 682-qualified mechanical seals is designed as both pusher (i.e., O-ring equipped) and pleated bellows types; the two designs keep both new and old equipment in mind.


Fig.4. Different iterations of a modern
API 682-qualified cartridge seal are shown;
they can be accommodated in the tight
space of 5th Ed. API 610 process pumps.
Image source: AESSEAL.

CAPI seals incorporate the same standards-qualified seal face technology for not only 10th Ed. API 610 pumps, but also the limited-space 5th Ed. API 610 pumps and pump specification variants in between. These variants span more than four decades and six successive editions of API 610; innovation is clearly seen in the unconventional tapered pumping ring located between the dual-seal pairs in Fig. 4.
Innovative cartridge seals open the way for pumping equipment designed in the 1970s and 1980s to be retrofitted with the latest API 682-qualification-tested seal face technology. No stuffing box modifications are needed to accommodate even the most modern seals. Facilities intent on meeting virtually every type of local and federal regulatory emissions mandate can now safely do so within the constraints of finite and often limited budgets.
When the pump lengths in Figs. 1 and 5 dictate, intermediate bearings are employed; these bearings are located between the flange joints of the intermediate pipes in Fig. 5. As is the case with the bottom journal bearing, intermediate bearings are mounted on separate replaceable shaft sleeves. The intermediate column pipe is filled with lubricant; this liquid column provides lubrication to the journal bearings and also encases the drive shaft.

Fig.5. Zone0 pumps before installation.
Note the all-stainless steel construction
and suction strainer in the foreground.
Column bearings are fitted at flanges.
Image source : Egger Pumps

An internal oil “sump”—if well sealed—is superior to pumps utilizing product-lubricated bearings. Lubrication makes it less likely for bearings to run dry and produce high friction-induced temperatures in the event of suction blockages or malfunctioning sump pit level controls.
Vertical tank-mounted Zone 0 pumps
Several drive shafts can be threaded into one another to achieve the needed overall pump length between the shaft coupling and the impeller. Also, two or more sections are then connected by the intermediate flanges shown in Fig. 5.
To prevent fluid traveling up the shaft, many vertical pump models incorporate a simple disc that acts as a “liquid thrower.” At the drive shaft end, two angular contact ball bearings or a double-row bearing locate the pump shaft. The “high-temperature” option is not needed for the majority of Zone 0 pumps. It is shown here to recall its availability for hot services found in cokers and evaporation plants.



DESSERT: TEN SURE STEPS TO SUBSTANDARD RELIABILITY PERFORMANCE

Equipment reliability can be enhanced or jeopardized by many different actions, inactions, commissions and omissions. Reliability may be a hollow term to many. Still, first and foremost, a reliable plant is a safe plant.
Equipment reliability can be enhanced or jeopardized by many different actions, inactions, commissions and omissions. Fortunately, entire corporations have prospered because of a consistent and highly productive reliability focus. However, some companies have disappeared because they only paid “lip service” to reliability, or because company executives placed reliability concerns at the bottom of their priorities list.
Reliability may be a hollow term to many. Still, first and foremost, a reliable plant is a safe plant. Safety and reliability cannot be separated. While some of these actions, inactions, commissions and omissions may take a company close to the brink of failure, we believe that, when five or more of these factors combine, they are likely to push a company over the brink.
Here, then, are 10 sure steps to substandard reliability performance, in alphabetical order:
1. Benchmarking fix. Statistics? What statistics? Why call it a failure in the first place? Why not just call it a routine repair? All machines need repairs sooner or later, don’t they? We have no failures. We just do lots of maintenance.

2. Buying cheap notions. We always buy cheap. We can always fix it up if it does not work. Or we can always sell the whole plant to investors with lots of money. All we need are good lawyers and dumb buyers.

3. Confirmation bias. We listen to those who have figured out what we want to hear. We reward those who have gotten away with guessing the way we would want them to guess. Alternatively, we support those who find ways to blame “issues” on things other than our guesses. Also, we can always blame it on the manufacturer.

4. Imperfection argument. Nobody is perfect, and everything is relative. That is why we don’t even have to try. We must be OK doing what we have always done; if it was good enough for our CEOs in previous decades, it is good enough for us today.

5. Opinion support. We prefer to listen to opinions instead of facts. We allow our staff to commingle opinions and facts, and see no need to separate the two.

6. Overconfidence. Our failure record might indicate that we are not nearly as smart as we think, but nobody’s data-collection effort is perfect. Therefore, we are not concerned that our failure record could be flawed, and we do not lose sleep over the matter.

7. Repeat failure tolerance. My guys report to the operations department. The operations team is interested in production. As long as we produce, we are all happy. That is why we have spare pumps—one pump out for repair has no production impact.

8. Status quo preference. My boss was promoted by not making any waves. Because I also want to be promoted, I will not make waves either. Therefore, I just say that the failure record does not bother me. It has always been this way.

9. Team player demands. The guys who do not jump on my bandwagon just are not team players. At a minimum, I will see to it that their careers are redirected into dead ends.

10. Training permissiveness. I let my team players choose what training they need. The fact that they prefer Honolulu over Detroit is not one of my concerns, and travel is one of their fringe benefits.
These sure steps to substandard reliability performance may raise eyebrows. We tend to believe that we are smarter than we actually are. However, if you are introspective and note any of the above traits in your organization, you might consider listing them in order of importance. You might then proceed to map out an appropriate improvement strategy and, hopefully, stick to following the map.
This map is best summarized by noting how successful companies impart reliability to their machinery assets. Management in consistently reliability-focused work environments will ascertain that both the operating range and safety factor (SF) of a machine are fully defined. If, for example, this range has an upper throughput limit of 100% and an SF of 1.3, then the reliability-focused environment will not encourage, allow or reward operation at over 100%. Operating within parameters where an SF is not present can prove disastrous.


I do hope you enjoyed the brunch served today...though belated.
Will see you next week

Re: SATURDAY ENGINEERING BRUNCH 2 by codesport(m): 1:36pm On Aug 23, 2015
Too voluminous
Re: SATURDAY ENGINEERING BRUNCH 2 by Nobody: 4:10pm On Aug 24, 2015
This is why it is in Engineering section. It is not gossip.
Take time to read, or else the world will not not read of you.

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