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PT&P received an emergency phone call from a petrochemical plant in the Persian Gulf. There was a ½” gap between the load flange of the Constant Spring support and the Trunion of the process line while the plant was in operation (Fig 1). Our expert field engineer was immediately dispatched to the client site to investigate the issue. An inspection of the products in question revealed that the travel stop nuts were bolted down. This prevented the support table from moving and supporting the pipe (fig 2). Figure 1 Figure 2

Travel Stop Removal is one of the most important tasks that must to be done when installing a spring support. Travel stops should be removed after Hydro testing when the pipeline is at the “Cold Load.” When the stops are left in place, “piping loads” are transferred to the piping system instead of being absorbed by the springs. Some of the results of this are: • Damage to pump equipment • Stress cracking of vessel nozzles • Bearings in pumps failing • Compressor not staying in alignment • Seal failure at flanges • Overloading of adjacent supports In 30 – 40% of the plants that PT&P visits for site inspection or hanger maintenance issues, there is at least one spring hanger with the stops in place. (Fig 3) The possible reasons for this are: • Improper Installation • Failure to remove the stops after maintenance or hydro tests. • Travel Stops being too difficult to remove Figure 3: C-Type Variable Spring Can During Operation with Travel Stop in Place Figure 4: Variable Spring Hangers in New Installation The following procedures should be followed when installing spring cans. These can be used for either Variable Load supports or Constant Load Hangers which are supported from the top. Bottom supported constants are discussed below. 1. Attach upper attachment(s). 2. Insert load pin attaching the spring to the upper attachment(s). 3. Thread hanger rod into lower attachment. This will be a load column or a turnbuckle. 4. Weld or bolt on pipe attachment. 5. Attach hanger rod to lower attachment 6. Turn load column/ Turnbuckle until the spring starts to compress and every thing is at full tension. 7. The Travel Stops should be easy to remove at this point. For constants, the pin may be pulled out. For Variables, the stop will fall out. For more detailed instructions please see our installation and maintenance guides: Variable Spring Maintenance Guide Constant Spring Maintenance Guide For F-type Constants (Fig 5.) 1. Secure base plate of the constant to the supporting structure. 2. Loosen the installation bolt (if necessary). 3. After hydro-testing (if applicable), remove travel stop pin. 4. Loosen and remove the installation rod. Figure 5 For U type Constants (Fig 6.) 1. Attach base plate to supporting structure 2. Attach support platform to the pipe 3. If there is to be a hydro-test, perform the test at this point 4. After hydro-testing (if applicable), loosen the travel stop nuts to permit the full design movement Figure 6 It is also important not dispose of the travel stops once the springs are installed. They will be useful during scheduled maintenance. Anytime that you are going to open up a pipeline with springs on it, you should replace the travel stops. It reduces flange alignment issues, and prevents the spring from releasing its energy when you disconnect. We offer: • Site inspection – inspection of existing supports to determine their condition and recommend other changes. • Installation inspection – on site commissioning of installations to ensure that the hangers, supports, braces, expansion joints have been installed correctly • Problem Solving – We can help find the solution to your pipe support problems • Stress analysis • Pipeline Design • Installation PT&P can and has worked in many places around the US and the World; we have over 30 years of experience in the pipe support industry. We are confident in our ability meet any challenge that comes our way.

By Jerry Godina
January 26, 2011

Slide plates are designed to provide a low coefficient of friction between stationary structures and moving pipe supports. The plates provide a surface friction that has been carefully designed to provide for movements of the piping systems, due to factors such as thermal expansion. In this way, the slide plates allow the system to move with less force, keeping it in proper working order.

Assembly Basics
Slide plates are usually arranged in what is known as a ‘sandwich’ formation, which consists of an upper slide plate component and a lower slide plate component.

The lower slide plate may also be welded to a stationary support (i.e. structural steel member), which grounds the plate, while the other plate is attached to the moving component directly. As the system moves, friction is transferred at the intersection of the two plates.

When ordering, always specify the dimensions of the upper and lower slide plate. As a rule, the upper slide plate should be large enough to completely cover the lower plate at all times.

Recommended Applications / Temperature Limits
The recommended applications temperature limit is negative 320 fahrenheit to positive 500 fahrenheit with a low pressure load (PSI)

Different plates are suited for different temperature limits. While all plates have been rigorously tested for suitability within industrial settings, understanding the particular variables of that setting is vital to purchasing the appropriate plate for each application.

PTFE, 25% Glass Filled Slide Plates
These slide plates will handle temperatures from negative 320 degrees Fahrenheit to positive 500 degrees Fahrenheit.

The PTFE plates are ideal for cross beam and girder slip joints, air preheaters, penstocks, vessels, and other industrial and architectural applications.

Installation of PTFE plates is available in two configurations, the standard and custom. The standard assembly features two sets of 3/32” thick PTFE pads bonded to 1/8” carbon steel backing plates with a 1/2” lip for field welding. The custom assembly features 2 sets of 3/32” thick PTFE pads bonded to the specified backing material, with a minimum 1/2” lip for full welding.  If the desired thickness of the backing plate is not the standard 1/8,” those who are purchasing the plate should specify a different thickness when placing their order

Bronzphite® Slide Plates
-320F to +1100F with 5000 PSI

Bronze plates impregnated with graphite will also handle temperatures up to positive 1100 degrees Fahrenheit. Additionally, bronze plates are suited for high pressure systems with a load of up to 5000 PSI.

The bronze plate is available in a standard configuration, which consists of the bronze plate bolted to a steel backing plate, allowing it to be welded in the field. The plate is self-lubricating and durable, and is recommended for a variety of industrial applications, including pipelines, storage tanks, and dust collectors.

Graphite Slide Plates
Up to 1,000˚ F with 2000 PSI

For those systems which produce exceptional pressure and heat, pure graphite slide plates are recommended. With a range of up to 1,000 degrees Fahrenheit for ambient conditions, and 3,000 degrees Fahrenheit for inert settings, graphite slide plates can also handle up to 2000 PSI. The graphite plates come in two different configurations, the ‘bonded’ and ‘bolted’ assembly. The bonded configuration consists of a ¼” thick graphite pad bonded to a metal backing plate. The bolted configuration consists of a ½” thick graphite pad bonded and bolted to a metallic backing pad. Both configurations can either be tack welded or fully welded to support components.

Graphite plates are best for heavy infrastructures such as bridges, highway overpasses, railroad bridges, and airport hangar doors. Domes, roof slabs and corbels, vibration pads and other architectural features are also suitable applications. In the industrial realm, offshore drilling rigs, wind tunnels, and other heavy machinery benefit from graphite plates.

Marinite Slide Plate
Marinite can be used as the insulating material in hot piping supports. The most widely known grade for Marinite is grade P. Marinite-P is most often used as structural insulation because of its high dimensional stability. Marinite-P is incombustible, provides high insulation values, and high compressive strengths and is thus appropriate in high-load and high-temperature applications. The material minimizes decay, rust, and corrosion and it resists damage during installation and provides durable service. The material acts as a suitable insulator in fireproofing and heat processing equipment applications up to 1200°F (649°C).

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Objective

Test Results of the formation of ice on an uninsulated pipe carrying liquid nitrogen

Test Facility

A perspective view of the facility is shown in Figure 1. The test facility consists of a 36” long stainless steel pipe of 4 1/2” OD with 4” ID. The pipe ends are closed by 3/4” x 5 1/2” x 21” plates. The pipe is suspended from top using two pipe clamps.

Figure 1: Perspective View of the test facility

To simulate cryogenic condition for an extended period of time, liquid nitrogen from a tank is supplied through a control valve into the pipe at one end and the nitrogen vapor is allowed to escape through a 1/2’’ tube from the other end.

The test facility is set in our workshop area where large size doors allow cross ventilation maintaining atmospheric conditions.

A type “K” thermocouple is set between the pipe and the clamp near the liquid nitrogen inlet to measure the pipe’s outer surface temperature history. Simultaneously, the ambient room temperature, relative humidity, and dew points were measured.

Test Procedure

Liquid nitrogen was allowed to fill completely the stainless steel pipe first, followed by a steady flow of liquid Nitrogen. By adjusting the control valve to a point when the liquid Nitrogen ceases to exit through the vertical outlet tube, the pipe remained completely full of liquid Nitrogen throughout the test. This flow process caused a small fraction of the flowing liquid nitrogen in the pipe to change phase to vapor by gaining latent heat of evaporation from the ambient air and exited through the outlet tube. This maintained almost a constant pipe surface temperature over an extended period of time.

Metering scales were fixed radially outward at three locations (near the two ends and at the middle) along the pipe to measure the ice deposition depth as a function of time.

Results

Test results are given in Table 1. After the liquid nitrogen flowed into the pipe, the atmospheric moisture started forming ice on the outer surface of the pipe, end plates and clamps. During this test, the ice thickness varied between day and night. This is due to the daytime temperature being higher than the nighttime temperature.

Material Items

The variations of ambient and pipes surface temperature with time are shown in Figure 2. In each plot, the day and night durations are shown by arrows. After filling up the pipe with liquid Nitrogen, the pipe’s surface temperature started falling exponentially with time and it took almost 20 hours to reach an almost steady state with small variations following a trend similar to that of the ambient temperature variations during day and night.

Figure 2, Variations of ambient and Pipe’s outer Surface Temperature with time.

The variations of ice thickness with time at three axial locations of the pipe are shown in Figure 3. As it is to be expected, the rate of ice formation is higher at night (when the ambient temperature was 8 ~ 10 degrees lower than in the day time) than that during the day. From morning to early afternoon, as the ambient temperature increased, some ice melted, resulting in a decrease of the ice thickness. In the first night, the maximum thickness was about 1.5”; the average thickness decreased to about 1.25” during daytime while in the following night the average thickness increased to about 1.75” and decreased to 1.35” during the day time, when the test was stopped.

Figure 3, Variations of ice thickness at three locations with time

(a) Test facility without ice formation

(b) Test facility with ice formation

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Polyurethanes are different from most plastic materials in that they can be tailored to meet the requirements of varying applications. Soft elastomers in flexible foams with low density are used in cushions and bedding. Tougher elastomers with higher densities are used for soles of shoes and boots. Rigid foams are used in construction, automobiles, furniture, boating, and many other applications.

Polyurethane: History

The commercial potential of polyurethane chemistry was first recognized in the late 1930’s. I.G. Farben (Germany), ICI (U.K.), and du Pont (U.S.A.) developed a variety of applications. ICI introduced rigid foams in 1957. Production line insulation for refrigerators was introduced in 1963. In 1968 General Motors started making polyurethane bumpers for the Pontiac G.T.O. The combination of strength to support loads and thermal insulation made rigid polyurethane foam an attractive material for the cryogenic pipe supports required for major LNG facilities constructed in the 1970’s.

Polyurethane Components: Pipe Supports

The primary design parameter for the polyurethane component of a pipe support is density because this determines the compressive strength. As shown in Figure 1, on a log-log scale the relation between compressive strength and density is linear. Tensile strength also has a linear log-log relation to density. Because the loads on supports for larger diameter pipes are larger than those on polyurethane components in many other industrial applications, we require higher density materials. For components used in pipe supports with densities from 10 to 40 pounds/cubic foot (160 to 640 kg/cubic meter), particularly those produced in molds, the compressive strength is essentially the same in all directions. Thermal conductivity is another design parameter of concern for the pipe support designer. For rigid foam polyurethane’s, thermal conductivity increases with density. Fortunately, the 10 to 40 pound-density materials are less sensitive to the choice of blowing agent and aging, two concerns for industries which use low density foams to achieve very low thermal conductivity.

Laboratory Testing

Laboratory tests have been developed to characterize the important physical properties of plastics to help guide design and production. The table below shows the ISO and equivalent ASTM tests which are widely applied to rigid polyurethane foams.

Rigid Foam Production for Pipe Supports

Rigid polyurethane components are produced by mixing two liquids; polyisocyanates and a mixture of polyol, catalysts, water and/or a blowing agent, pigments and other additives. Companies with experience in blending these chemicals can tailor them to the specific application. When the chemicals are combined under controlled conditions, an exothermic reaction begins and the foam begins to expand. With proper control of conditions the reaction continues to completion and a solid product is obtained.

The primary factors which manufacturers must control are temperature, accurate metering of the liquids, mixing, curing time and freedom from contaminants. Many machines have been developed for manufacturers to use for both control and efficient production. At Piping Technology we use RIM (Reaction Injection Molding) machines which provide excellent mixing, temperature control and metering of the chemicals. Our large inventory of molds give us the ability to provide proper geometry with a minimum of waste, reproducible results and maximum productivity of the workforce. Assembly line techniques can be applied when quantities justify this approach. The cure time before de-molding depends on the size of the components.

Chemistry

Rigid polyurethane foams have a relativity large amount of cross-linking as the foams expands. Suppliers of the chemicals control the degree of cross-linking by functionality (higher functionality produces more cross-links) and molecular weight of the components in the blend. Figure 2 shows a photomicrograph image of a cut piece of rigid foam. The closed cells formed during cross-linking can be seen. These rigid cells provide the strength and the interior space provides low thermal conductivity. Water can be used as the blowing agent for foam in this 10 to 40 pound-density range. This avoids the need to use chlorofluorocarbons which were so important in the production of 1 to 2 pound-density insulation prior to modern environmental regulation.

Permeability

The water vapor permeability of rigid polyurethane foam is low but pipe support applications often have a very large temperature differential between the cryogenic fluid inside the pipe and the climate outside the insulating system. For this reason, pipe supports designers use impermeable facings (galvanized, rolled shields), with low-permeable coatings and linings to separate the moisture-laden air outside from the polyurethane component which is in contact with the cold pipe. An effective moisture barrier on the warm side is particularly important for this type of application.

PT&P: Polyurethane Production Capabilities

Piping Technology and Products has a complete manufacturing facility for production of polyurethane components required for pipe supports. We invite our customers to visit our facility and observe the fabrication of insulated pipe supports of all types. Our engineers will be happy to discuss the use of rigid foam polyurethane for cryogenic supports.