THE COFLEXIP FLEXIBLE STEEL DRAIN PIPE

Transcription

1 THE COFLEXIP FLEXIBLE STEEL DRAIN PIPE Page1/9

2 1. COFLEXIP DRAIN PIPE The Coflexip Drain Pipe is made in internal diameters of 3, 4, 6 and 8 inches. The structure is composed of an articulated stainless steel 304, interlocking, spiral wound inner carcass covered by an outer extruded sheath of Rilsan Nylon 11. The strong inner carcass flexes like hose but will not kink or collapse. However, this inner member is not designed to prevent leakage. Instead this is accomplished by using a thick outer protective thermoplastic jacket made of Rilsan Nylon 11. The nylon is extruded over the inner carcass and forms a water tight seal. The nylon is sufficiently strong to withstand the industry standard of 30 psi W.P. / 60 psi T.P. It is also chemically inert to 100% aromatics (benzene, tuolene, xylene) caustics, Bromide, Methyl tertiary Buthyl Ether (MTBE), trace elements of acids and hydrogen sulfide. The end-fittings are made of mild steel and covered with several coats of anti-corrosion paint. Each is a single piece assembly which is swaged around the drain pipe. A slip on, 150# ANSI, rotating raised face flange is fitted behind the neck. The rotating flanges give ease of alignment of the bolts when connecting to the rigid piping flanges and also avoid any torsion in the flexible itself. DESIGNATION 1. Inner interlocked stainless Steel carcass ( anti collapse ) AISI External plastic sheath (RILSAN) Page2/9

3 2. DRAIN SYSTEMS Two commonly utilised drain systems are composed of jointed rigid pipe or rubber hose. Each has its own inherent major problems : 2.1. JOINTED RIGID PIPE A) This system uses sections of schedule 40 rigid pipe with swivel joints. The swing or swivel joints are fairly uniform in design. The assembly can move in a vertical plane only, with a scissors like action. Major deficiencies are as follows : Leakage of the swing joints is the major shortcoming. Continued movements affect the packing circumventing each seal on each swivel. Since the joints are not easily accessible, preventive maintenance cannot easily be performed. A second problem is corrosion and/or binding of the joints. Binding affects roof floatation by restricting action or causing roof rotation. The problem is increasing in importance because of tightening environmental regulations. Finally, in colder climates, water freezes inside the pipe and either further aggravates the swivel leakage or bursts the pipe and/or seals. B) A hybrid to the swing or swivel joint system utilises jointed rigid pipe connected with flanged hose unions. These systems have eliminated some of the problems associated with the seals and bearings of swing joints but have their own specific major drawbacks : The system requires four (4) joints which in turn require a minimum of eight (8) flange connections - each which have the potential to leak. With any joint, flow rate will be reduced. The Hose is a composite hose whose outer jacket, through flexing, can allow seepage. Failures can occur in freezing conditions. The short 90 degrees bend radius can accumulate foreign material. The system takes longer to install and requires further fabrication which drives up total installed cost. Page3/9

4 2.2. RUBBER HOSES Rubber hoses were originally installed to overcome deficiencies of jointed pipe. Two grades are sold, 70% aromatic and 100% aromatic resistant. Seventy percent uses Buna-N- rubber cover and inner core ; 100% uses Viton Fluoroelaster cover and/or Buna-N, Viton inner core. In order to prevent hose floatation inside the tank, ballasting chains extending through the ID or lead weights built into the construction are used. Major deficiencies are as follows : A) Because of floatation, the hose can be caught beneath roof legs with resultant kinking, crushing or other damage. B) Incorrect hose length can also cause kinking. If a hose is too short, kinking occurs next to end-fittings at the shell connection when fully extended. If too long, kinking can occur just below the suspension clamp where the end fitting is attached to the sump. If the roof is on low working legs, buckling can occur along with the kinking. C) Collapse of the inner core is also a problem if the outer jacket is perforated or slit. Differential pressure can cause tank liquid to pass into the structure. This has been a particular problem with 6" ID hoses. D) As stated earlier, hoses are resistant to either 70% or 100% aromatics. Seventy percent aromatics hoses have been used incorrectly when 100% aromatic protection is required. E) Frozen water inside a hose will cause bursting. F) Ballast weight inside hose can break loose and cause an unequal distribution of weight, resulting again in kinking. G) The hose when in a coiled position, will cause one of the double helices of spring steel wires embedded in the hose to severely compress the inner carcass. The other wire will open up and affect flexibility. I) The outer cap of stainless steel will cause excessive abrasion on tank bottom resulting in the wearing away of the epoxy coating or the scuffing of the clean steel under scale which will increase the rate of corrosion. When a scuff covering is placed over this, it could tear loose, damaging pumps or mixers. Page4/9

5 3. THE ADVENTAGE OF COFLEXIP FLEXIBLE STEEL DRAIN PIPE Coflexip Flexible Steel Drain Pipe is installed in a single continuous length without ballasting or other devices. Unlike drains made of rigid pipe, there are no swivel connections to maintain. The flexible drain pipe will never interfere with equipment inside the tank when the roof comes down. Even though it flexes freely, the flexible pipe will always come to rest in the same position and pattern. Each Repeatable Lay Pattern is custom-engineered for each specific tank installation. It is accomplished through computer assisted drawings, based originally on scale model tank testing, for which the customer provides either tank prints or accurate tank measurements. The computer design can be scaled to any conventionally sized, commercial, open floating roof, storage tank. Roof sump design, heating coils and rigid pipes extensions can be matched to comply with tank information received. The drain pipe itself has no memory ; the Repeatable Lay Pattern is directed by pipe structure, length, angles and roof action forces. The articulated stainless steel 304, interlocking spiral wound inner carcass with the Rilsan Nylon 11 jacket has no preferential weak points of over bending. Compressive forces at any one point are uniformly transmitted without reduction in internal diameters. Angles of pipe attachment to roof sump and tank shell are effected by standard 180, 90, 45 or other degreed flanged elbows. The selection and orientation of these angles act on the pipe, establishing the lay pattern configuration and locking the pattern into place relative to the roof position. Artificial lay patterns, induced by pipe twisting or coiling, are never done. Upward roof movement applies tension, which pulls the Coflexip configuration from a horizontal to a vertical plane. Descending roof movement applies compression, forcing pipe back to horizontal plane and original induced position. The Repeatable Lay Pattern is thus a predetermined operating configuration, which functions in a predictable and recurring fashion in response to the movement of the floating roof. The lay pattern is customised for each tank based on tank size, number and location of roof support legs. The pattern is established by adjusting the length of the pipe and the angle of connections to the roof sump and the lower drain. The Coflexip pipe is tailor-made to the tank with its lay pattern designed from specific tank measurements. It is a flexible, "single-unit" that moves in harmony with the roof. Once installed the pipe will always lay in the same pattern. The pattern is not affected by the product moving during filling, draining or agitation. It will not be altered if water freezes inside the pipe. Page5/9

6 A reliable drainage system is indispensable for floating roof storage tanks. An improper roof drain impairs tank operation and threatens the safety of the stored products. This can result in considerable down time, contaminated product, environmental problems and repairs which can drastically reduce profitability. The Coflexip maintenance free drainage system, through the Repeatable Lay Pattern, means reliability. Consider some of the advantageous features our drainage systems offers : Selection of the correct length eliminates possibilities of over bending or end fitting pull-off or damage. Contact with roof legs will not occur because of the permanent lay pattern. This will eliminate crushing and kinking of the pipe. 3.1 COMMONLY ASKED QUESTIONS What effect does the Repeatable Lay Pattern have on the floating roof? There is none that we know of. The tests show shear forces on the flange bolts for one 4" ID x 80' Coflexip Drain Pipe to be 930 psi each. The design parameter of bolts is 10,000 psi to 12,000 psi. Unlike rubber hose, Coflexip lines need no ballasting. The Coflexip Drain Pipe is never twisted or coiled as with rubber hose and will not contribute to roof rotation. Stiffness counters floatation on a Coflexip Flexible Steel Pipe. The flexible pipe is locked in place relative to roof position, either under tension or compression. Since the pipe is locked in place relative to roof position, the vertical and horizontal displacement remains constant. What effect is caused by internal mixers or flow velocity? There are no known effects. Tests on the Repeatable Lay Pattern in face of 11 ft/sec flow through 36" ID at 50,000 bbls/hr, show no effect on operation. What about flex fatigue? The interlocking articulated carcass is not subject to flex fatigue. Tests by major oil company show no failure after 12 million flexation / rotation tests at operational pressures. How tough is the nylon jacket? Abrasion resistance Temperature Chemical Rilsan is times superior to rubber in taber abrasion tests + 23 F to F, or the normal working temperature range of a tank 100% aromatic resistant. It cannot be attacked by benzene, zylene, tuolene, caustics, bromines, trace elements of acids or hydrogen sulfide Page6/9

7 Is there a possibility of abrasion to the tank bottom? Although Coflexip's outer nylon jacket is highly resistant to abrasion, it is not an abrasive material. The nylon outer sheath by nature, is very slick. With the presence of hydrocarbons this jacket will be enveloped with an even greater lubricating surface, thus reducing any friction that may exist between the Drain Pipe and the tank bottom. How difficult is the Drain Pipe to install? If the necessary prep work (which includes setting up the flanged elbows) is done, it should only take 60 to 90 minutes to complete the installation of the Coflexip Drain Pipe. Note that end connectors have rotating flanges for easy bolt hole alignment. This is done because it is extremely difficult, if not impossible to twist the Coflexip Drain Pipe. How strong are the end-fittings? End-fittings are designed to accept, with safety margin, all operational pressures and torsional loads of the pipe itself. Damaging pull to a structure will not effect the end-fitting's integrity. How is the length of the Coflexip Drain Pipe determined? The Coflexip Drain Pipe is positioned into its Repeatable Lay Pattern by flanged piping connections from the tank shell and sump. The length is then set by a Coflexip "Rule of Thumb" which will give the correct flexible pipe length which will respond to the forces applied at these connections. The "Rule of Thumb" length are set per the below chart : 3" ID 4" ID 6" ID 8" ID Actual height of the tank + 6 ft Actual height of the tank + 8 ft Actual height of the tank + 12 ft Actual height of the tank + 14 ft Why is a "Bending Restrictor" used? A Bending Restrictor is utilised for very high tanks requiring very long Coflexip Drain Pipes. This insures that the resulting weight increase of the Drain Pipe will not cause over bending behind the end-fitting at the sump connection when in the highest roof position. The clamp keeps the flexible pipe in a natural, working, bend radius. Page7/9

8 What tank measurements are needed? To design the customised Repeatable Lay Pattern, specific information from each tank is needed. Computer modelling is performed based on the tank prints, but if not available, measurements of the tank must be taken. The following information is necessary : A plan view of tank top, with diameter and layout of all roof support legs. A sectional side view, giving tank height + upper and lower roof positions. A sectional side view of roof structure with roof sump detail. Orientation of sump connection and shell outlet connection No two tanks are identical and it should not be assumed that simple length or coil calculations will suffice. Each pipe is customised and therefore measurements or tank prints are necessary from each tank. Before installing the Drain Pipe, it is imperative that the drawings including the Repeatable Lay Pattern drawings, match the tank in question. To ensure proper operation of the Drain Pipe, there must be an identical match SUMMARY The Coflexip Flexible Steel Drain Pipe thus has the following major benefits : Has the properties of metallic pipe Is chemically inert to 100% aromatics Does not/will not kink Requires no ballasting Is one continuous length with only one flanged connection at each extremity Is corrosion resistant Resists abrasion Resists freezing temperatures Has "unique" Repeatable Lay Pattern Has no preferential weak points due to metal fatigue Ease of installation Maintenance free Increased tank capacity. The floating roof can be operated at a minimum height which is smaller than with swing or jointed pipes Page8/9

9 4.BEND RESTRICTORS DIMENSION CHART (IMPERIAL) ID PIPE (INCHES) (HD) 8 C (Feet) MBR + 3' B (Feet) EF + (1.57 x C)* A (Feet) EF + C * (1.57 is a constant) DIMENSION CHART (METRIC) ID PIPE (mm) (HD) C (mm) MBR mm B (mm) EF + (1.57 x C)* A (mm) EF + C * (1.57 is a constant) Page9/9