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FAQ

Re.  305/2011/EU Construction Products Regulation (CPR)
On July 1st 2014 it became a legal requirement for fabricators of structural components used in the construction industry to comply with the requirements of the CPR & CE marking requirements. While there are exceptions to this it is not at all clear to what degree it should be applied to the manufacture & supply of pipe supporting equipment & associated steel work.

To be very clear about the situation, Pipe Hangers & Supports as defined by EN 13480-3 section 13 & associated appendices are intended solely for the purpose of supporting & distributing the weight & forces generated by the piping into the primary structure. They also allow for the displacement of the piping during plant operation. The connection point to the steel structure can be by direct bolted or welded attachment or by the placement of secondary steel members to provide a convenient connection point.

All attachments to the primary structure are either pre-fabricated by the structure fabricator or else made at site during the installation of the pipe supporting equipment.

The loads & forces imposed on the primary structure by the pipe hangers & supports are known to & considered by the primary structure designer.

Pipe Hangers & supports are therefore classified as a ‘second-fit’ to the primary structure & as such do not provide or enhance the structural integrity of the primary structure. They are designed in accordance with the requirements of BS EN 13480-3 which is harmonised with the “Pressure Equipment Directive” (“PED” 97/23/EC). CE marking under the PED is limited to parts that are welded to the pressure containment part.

Because of this Pipe Hangers, Supports & associated secondary structural members do not fall under the requirements of either the CPR or EN 1090 when supplied by the pipe hanger manufacturer.



DOES IT MATTER IF THE SPRING RATES DIFFER FROM THE RATES SELECTED IN THE STRESS ANALYSIS?
When running the pipe stress analysis programme, the user will choose a specific support vendor and the analysis program will choose spring rates from that vendor's catalogue. When using a different vendor, spring rates will be slightly different. This is usually considered acceptable provided the spring rates are reasonably close. If a different vendor is chosen, the analyst has the option of re-running the analysis specifying the selected vendor's catalogue, but this is not usually considered necessary. Variable effort supports are manufactured using standard spring coils from stock and it is impractical to make one-off designs using non-standard spring rates.


FOR CRYOGENIC SUPPORTS, WHAT TESTS ARE NORMALLY CARRIED OUT ON BONDING AND VAPOUR BARRIERS, AND WHAT ARE VAPOUR STOPS?
We use proprietary adhesives for both processes and we apply these adhesives according to the manufacturers’ recommendations, so there should be no reason to do any testing on either process, apart from visual inspection.

We have in the past tested the bond strength of the PUF to PUF joints, and, if the client wishes, we can test the joint strength and arrange for third-party testing of the foil to PUF bond.

With regard to water-vapour permeability – the foil we use is fully tested and rated so we do not consider it necessary to perform independent testing.

It is vitally important that all joints are made correctly and thoroughly on site by the installation contractor otherwise moisture will be drawn into the insulation and cause major icing problems. Joints can also be reinforced using products such as Foster’s Mastafab or Temati’s Scrimtex in combination with Foster’s 90-66.

Vapour stops are applied to the end of the low-density insulation by the installation contractor to prevent vapour from spreading along the pipe. It is standard practice to apply  vapour stops each side of pipe supports, valves & flanged joints as it is usually accepted these items will need maintenance at some time in the life of the plant. Vapour stops consist of a short section of 'sacrificial' insulation each side of the support or valve. This can be removed easily without causing damage to the main insulation.

A coat of sealant is applied to the exposed surfaces of our cryogenic supports during manufacture to prevent moisture damaging the insulation. 


IS 'PUR' OR 'PIR' BETTER FOR CRYOGENIC SUPPORTS FOR LNG TERMINALS?
PUR (polyurethane) and PIR (polyisocyanurate) are both cellular insulation materials produced from a catalytic self-polymeric reaction of isocyanate.  They are widely used in chemical, alkene cracking plants and LNG storage and transportation where excellent cold insulation capability is required.

The difference between PUR & PIR is that PUR is a much stronger material able to absorb impact. PIR is a very brittle material that is normally used as low density line insulation but it is not suitable for use at pipe support locations where high loading has to be absorbed.

PUR is moulded by Bergen Pipes Supports to the required shape & so has no residual stress. PIR is generally cut from bun stock which can have high residual stress & can cause cut pieces to distort. Their operating temperatures are similar (PUR’s range is -196 ~ 140oC and PIR’s is  -196 ~ 160oC).

PIR has better fire resistance than PUR, but PUR is acceptable for LNG applications.


WHY IS NEOPRENE NOT RECOMMENDED FOR COATING SPRINGS?
Neoprene is a substance that is hazardous to health and has been outlawed in the UK – it is also very poor as a protective coating, having inferior properties to the plastic coating we use.


WHAT IS THE MAXIMUM OPERATING TEMPERATURE FOR PLASTIC COATED SPRINGS?
The maximum operating temperature of springs, whether coated or not, is limited to 80 degrees C.


ARE LOADS FOR STRUTS AND SNUBBERS STATIC OR DYNAMIC?
Struts & Snubbers are designed on the basis of dynamic loading – therefore the loads stated in our catalogue are ‘dynamic’ loads.


WHEN FILES ARE EXPORTED FROM PSDESIGNER TO PSLCAD ARE THE WELDS SHOWN IN PSLCAD?
If a .dxf file is exported from PSDesigner, and the option to show the weld size is selected in PSDesigner, the weld will be shown. If using PSLCAD directly, the weld size needs to be added manually.


CAN PSG MANUFACTURE NON-STANDARD PIPE CLAMPS?
Yes, we make our own tools for forming pipe clamps so we can make a pipe clamp to suit any size of pipe up to approximately 1400mm diameter.


ARE SPRING HANGERS SELECTED FOR HOT DESIGN OR COLD DESIGN? 
The weight of the pipework doesn’t change when it gets hot, but the pipes move up and down due to thermal expansion. When using simple variable effort supports, the supporting effort necessarily changes as the pipe moves up or down due to the spring rate of the supports. So it is not possible to exactly balance the pipe with the supporting effort from the springs in both the cold and hot conditions. You therefore need to decide in which condition you want to exactly balance the weight of the pipe.

For steam pipes (especially high pressure steam) the material strength is much less at high temperature, so it is usual to have the support loadings exactly matching the weight of the pipe in the hot condition (hot design) and accept the load imbalance and consequent higher terminal point loadings in the cold condition.

For pipes where there is no appreciable reduction in material strength at the design temperature, designers sometimes choose to use the cold design method where the loads balance exactly in the cold condition. This should in theory make the pipework installation easier, as releasing the springs from their locked positions should not result in significant deflection of the pipework since the loads should balance correctly in the cold condition. There will be a load imbalance in the hot condition.

It is good practice to select supports towards the middle of the travel range. Normally one should aim to centralize the cold to hot range rather than just the hot load. Doing this will help to avoid the springs “topping” or “bottoming” out due to any difference between actual and theoretical pipe weight.


ARE PSG'S SUPPORTS IN ROHR2?
Yes, PSG's data for spring hangers and spring supports has now been implemented in ROHR2, supplied by SIGMA Ingenieurgesellschaft mbH. ROHR2 users can update the program via the implemented update function.


IS THERE A LIBRARY OF PSL SUPPORTS IN CATIA 3D SOFTWARE?
CATIA is a 3D solid modeling tool and would be used for designing products e.g. gearboxes or turbines, rather than for modelling a whole plant. We do not have a library for CATIA and there are no plans to create one.

Direct 3D dxf export from our software is planned for the end of 2009, and we believe the 3D images created will be able to be read by any 3D program.


IS PSG INCLUDED IN CAESAR II?
Yes, PSG's variable effort support data is included in Caesar II Version 5.00, and will also be in the new Version 5.20 when this is released (our data base is shown as 'Pipe Supports Ltd'). In Caesar II Versions 4.50 and earlier PSG's supports are listed under the name 'Comet' (this used to be PSG's brand name). This appears as number 17 in the list of spring hanger vendors. For users who wish to select hangers using imperial units our US data base is available under option 22, 'Pipe Supports US'.

To find out more about Caesar II please click here.


ARE PSG'S SUPPORTS COVERED BY CE REGULATIONS?
As our supports have no means of ‘self actuation’ they do not generally fall within the CE requirements. Exceptions are items that are welded to the pressure containment boundary – lugs on pipes or reinforcing pads for example. In such situations the material needs to be produced by a CE accredited mill and the certification needs to carry the CE mark.


DO PSG COMPLY WITH AWS WELDER QUALIFICATIONS?
AWS = American Welding Society standard, which covers welding/welder qualification requirements for use within structural steel fabrications.
All of our procedures/welders are qualified in accordance with ASME IX which is considered to be a superior specification & hence qualification. ASME = American Society of Mechanical Engineers - Section IX applies to welding qualification for Boiler & Pressure vessels.


ARE MECHANICAL SNUBBERS PREFERABLE TO HYDRAULIC SNUBBERS, WHICH CAN SUFFER FROM OIL LEAKAGE?
It is a fact that hydraulic snubbers require maintenance over a period of time in order to replenish the natural leakage of hydraulic fluid. Pipe Supports Limited is working towards a snubber design that will help to minimize the need for such maintenance. However, it cannot be totally eliminated.

In the USA, where there has been very long experience of operating nuclear power plant and where snubbers have been the subject of much discussion and review, there was a move towards mechanical rather than hydraulic snubbers. It was found, however, that a mechanical snubber is also subject to operational problems. The mechanism is prone to wear and fatigue and generally when a mechanical snubber fails in service it seizes and prevents the pipe from being able to move which in turn leads to damage to the piping and connected plant.

Hydraulic snubbers conversely fail in a ‘free’ state – the snubber continues to move with the pipe at the expense of slightly increased drag. However, the resultant stresses on the pipe during normal operation are insignificant. The problem with a ‘failed’ hydraulic snubber is that when the ‘event’ happens it can only provide notional damping by the air that is trapped within it.

Hence in the States there were significant efforts made to minimize the number of snubbers used.

Pipe Supports Group do not intend to manufacture mechanical snubbers; we do, however, have a relationship with a Japanese manufacturer who is willing to supply us mechanical snubbers, although our price will not be as competitive as it would be for hydraulic snubbers.


WHAT MATERIAL SHOULD BE USED FOR SPRINGS IN LOW AMBIENT TEMPERATURES?
There are a wide range of views on what material should be used for springs in low ambient temperatures. Springs manufactured from the materials which are normally used to make coil springs (silico-manganese or low alloy spring steels) will have quite low impact toughness (circa 5J) but the pertinent question is "does this matter?" We have been given the following advice from the Institute of Spring Technology in UK. "For a failure to occur from impact loading, it is necessary for the material to be loaded suddenly and for some plastic deformation to be initiated. A spring is only loaded elastically and so the impact toughness does not matter." Because a spring is inherently elastic, impact loading is absorbed by elastic deformation of the spring and the shock loading which is necessary to cause brittle failure is not likely to occur. 735A51 (Chromium-Vanadium) steel gives higher impact toughness (typically 12J) than other spring steels, though this is still not particularly tough. We have used this material on some contracts where the springs are being used in low ambient temperatures. There is a cost penalty in using this material, and there may also be some delivery implications depending on the scope of supply.

Spring coils can also be made from stainless steel grades which have much higher toughness, but these materials have a lower allowable stress so the spring will be made from a larger bar diameter and will be to generally larger dimensions at very much higher cost. With regard to experience of failures of springs in low ambient temperatures, we had one instance of a spring coil failure on a support in Siberia, but our investigation into the failure found that it was due to a quench crack which had not been spotted during our spring coil supplier's crack detection, so this failure would still have occurred if the plant had been in the tropics - the failure was not due to temperature. We would offer spring coils plastic coated for corrosion protection, not galvanized as this process can cause hydrogen embrittlement in high strength steels. 


WHAT SOFTWARE DO YOU USE FOR 3D-MODELLING OF PIPE SUPPORTS?
Our PSDesigner programme can be interfaced with Aveva's PDMS/MDS and Intergraph's PDS/SupportModeler software. Support assemblies are created from parametric libraries of PSG's supports and automatically placed in the 3D models.

Further sub-questions:
DO YOU HAVE A PROGRAMMED SELECTION SYSTEM BASED ON THE STRENGTH CALCULATION OF THE HANGER?
Yes, PSDesigner.

DO YOU HAVE A PROGRAMMED SELECTION SYSTEM BASED ON THE STRENGTH CALCULATION OF THE STEEL BEAM?
No.

CAN 2D-DRAWINGS BE OBTAINED FROM 3D-MODELS?
Yes, this is done by Intergraph's SupportModeler and by Aveva's MDS. PSG can manufacture to the MDS or SupportModeler drawings.

IF THE DESIGN CHANGES DO YOU REVISE THE 3D MODEL?
No, the 3D model is used by the client. PSG provide the selection/design program which interfaces with the 3D model. Revision of the 3D model is the responsibility of the client.


WHAT SOFTWARE DO YOU USE TO DRAW 2D DRAWINGS OF PIPE SUPPORTS?
We have two programmes. PSLCAD is an in-house program for drawing PSG's standard support components within AutoCAD. PSDesigner is an in-house program which automatically designs complete support assemblies. this is a stand-alone program which does not require a separate CAD program. Both PSLCAD and PSDesigner are provided free of charge to customers.


IS THERE AN ALLOWABLE ROTATION OF THE HANGER ROD RELATIVE TO THE SPRING CAN FOR SPRING HANGERS? I HAVE A SITUATION WHERE I HAVE VERTICAL MOVEMENTS COUPLED WITH LATERAL AND AXIAL MOVEMENTS. I AM WONDERING WHAT THE THRESHOLD OF ANGULAR MOVEMENT OF THE HANGER ROD RELATIVE TO THE SPRING CAN IS BEFORE I CREATE HINGES WITH WELDLESS EYE NUTS ON BOTH ENDS OF THE HANGER ROD.
Normally the allowable rotation is 5 degrees in all directions. By consideration of lateral movements with regard to the orientation of the various components it is normally possible to maximize the distance between pivot points to suit the direction of maximum displacement. For example, if connecting to a lug plate via a pin, the rotation of the pin should coincide with the direction of largest lateral movement.


WHAT METHODS ARE USED TO SUPPORT SLOPING PIPELINES?
The best solution depends on the amount and length of slope, whether the supports are fixed or sliding, etc. Angled pipe shoes are supplied for small quantities, but they are generally avoided for larger quantities due to the variety of different sizes involved, and the extra cost. Roller supports can be a good solution. If suspended supports can be used then rods and clamps (with or without spring supports) offer another solution, with the movement of the clamp on the rod making allowance for the slope of the pipe.


WHAT IS A SWAY BRACE?
A sway brace is a special type of variable effort restraint and is built around a standard or non-standard spring. It is used to restrain piping or equipment and is not intended to support.

The construction of the sway brace enables a pre-loaded spring which sustains both compression and extension displacement to provide a pre-determined restoring force.

For example, a pipe that is exposed to cross wind will sustain high transverse force during strong winds. If the pipe is subject to thermal expansion and contraction it will have a certain amount of flexibility. If allowed to displace freely during strong winds the pipe may become unstable and possibly sustain permanent deformation.

By installing a sway brace the pipe can be held in position during the application of forces less than the pre-set force within the spring. At higher forces the pipe will be allowed to displace but the further from its neutral position it is pushed the greater the restoring force will become.
When the storm recedes the sway brace will push or pull the pipe back to its neutral position.

Specifying Sway Braces: Like all devices that exert a restoring force to a pipe the magnitude of force that can be applied and the amount of acceptable displacement will be decided by the allowable stresses within the pipe. This information will be defined by piping engineer during his analysis of the system.

The level of pre-load within the sway brace shall be defined by the minimum force required to restore the pipe to its neutral position; it may be a function of the dead weight of the piping and the magnitude of frictional resistance thus created at sliding surfaces or it may be the amount of force required to restore an unstable, out-of-balance mass.

For simplicity, if we consider a pipe crossing a bridge structure, thermal expansion of the pipe is predominantly in the axial direction and so the pipe is carried on three sliding supports each having a coefficient of friction of 0.1. The total supported mass of the pipe is 10,000kg. Therefore the frictional resistance in the transverse plane is 1000kg.

If we select a sway brace that delivers a pre-load of 1000kg and has a spring stiffness of 100kg/mm the minimum transverse resistance to sliding is 2000kg increasing by 100kg/mm of displacement.

Assume now that the wind pressure on the pipe exerts a force of 2500kg; the pipe will displace by 5mm. If the pipe is sufficiently flexible and without the influence of the sway brace it may not be able to generate sufficient elastic energy within itself to return back to its neutral position. Subsequent axial loading may then cause further deformation of the pipe because it is not offering a rigid shape to the applied force.

With the sway brace installed the restoring force is at least that which is necessary to overcome friction and so the pipe is returned to its neutral position.

When in the neutral position the sway brace exerts zero restoring force and so the pipe is free once again to move with the thermal cycle.
Any practical combination of pre-load and spring stiffness may be defined and any spring within our standard range of variable and constant efforts supports can be applied to the product.

In our Variable Effort Supports product catalogue we offer a basic range of sway braces but it will normally be necessary to design the device to suit the specific requirements of the customer.


ARE PSG’S SUPPORTS AVAILABLE IN OTHER SOFTWARE LIBRARIES?
Our support products are included in the following programmes:

• SupportModeler programme for 3D modelling of hangers supplied by Pelican Forge, which is owned by Intergraph Corporation.

• Caesar II stress analysis programme produced by COADE. PSG's variable effort support data is included in Caesar II Version 5.00 under ‘Pipe Supports’, and will also be in the new Version 5.20 when this is released. In Caesar II Versions 4.50 and earlier, PSG's supports are listed under the name ‘Comet’ (this used to be PSG's brand name). To find out more about Caesar II please click here.

• Autopipe 3D piping analysis programme, supplied by Rebis.

• Triflex piping analysis software supplied by Software Solutions.

• Logisterion P10 piping analysis software.


PLEASE COULD YOU EXPLAIN YOUR ‘SPRING SELECTOR’ PROGRAMME?
Spring Selector is a C++ stand-alone programme that is used to select variable and constant effort supports.

In the centre of the dialogue box all possible spring selections are shown for the load and movement selected. If you would prefer to choose one of the other spring sizes shown, you can select it by clicking on it.

In the top left of “Spring Selector” a drop-down box gives the choice of spring types. The representation of the type of spring below the drop-down box alters when a different selection is made.

To the right of the list of spring sizes, the coloured arrow indicates where the operating movement of the spring is in relation to its total operating range (i.e. the grey area, with the overtravel shown at either end for variable effort supports). In the example shown the bottom of the arrow shows the preset position, and the top of the arrow shows the operating position. The direction of the arrow indicates that there is an upward movement. For a downward movement the arrow will point downwards (and the preset and operating positions will be reversed). The optimal position of the arrow is in the middle of the total operating range.


IS THERE ANY DIFFERENCE BETWEEN CIRCULAR & RECTANGULAR PTFE SLIDE BEARINGS?
Neither shape offers any great benefit, but a square, rather than circular, shape can be more economic as there is less scrap when cutting from a square sheet.

The key factor is to ensure adequate surface contact area. Please refer to our catalogue for guidance on allowable bearing pressure, and take account of ambient temperatures since these will also affect the allowable bearing pressure.


WHY ARE PIPE SUPPORTS USED?
People around the world use pipe supports and restraints; in fact they spend somewhere in the region of £150million on ‘engineered supports’ each year.

The majority of pipes that we support and restrain are actually long thin pressure vessels operating at high pressures and temperatures, and occasionally at very low temperatures. In general they connect one large piece of equipment to another and facilitate the flow of fluid between the various processes. In some cases we supply supports for pipes that operate at temperatures as high as 850°C and diameters large enough to walk through.

During the operating cycle of the plant there is inevitably a change in temperature; when the plant is not working it is at ambient temperature and when it works it operates at a different temperature. Even changes in temperature between day and night can have significant effects.
Almost all materials expand or contract as their temperature is increased or decreased. A pipe that carries steam from a boiler to a turbine heats up from room temperature to 570°C between not working and working. This change in temperature will cause the pipe to expand by approximately 7.5mm/m, though the change is most prominent in the length of the pipe rather than in its diameter.

Imagine if the pipe could not expand or contract freely, the force generated in preventing the expansion to take place will cause substantial damage to either the pipe or the equipment at each end of it!

Consider the pipe work in a power station and liken it to your own central heating system; fluid is pumped around a closed system. In the boiler water is heated under pressure allowing its temperature to be increased to over five times the normal boiling temperature of water. An escape of steam under these conditions would simply cut a man in half.

This steam passes through the pipe work into the turbine where the pressure drives the turbine and generates the electricity. Inside the turbine the pressure is reduced and the temperature of the steam decreases. It is then sent back to the boiler where it is heated up again and so the cycle continues. The greater the demand on the power station, the higher the operating pressure and temperature will be.

The analogy with the central heating system; when your heating comes on or goes off you hear all sorts of creeks and bumps as the system heats-up or cools-down. That is simply because the piping is expanding and contracting between fixed points; the noises are due to the pipe moving against the joists and floor-boards of your house.

On a large, coal fired power station such as Drax in Yorkshire the boiler may be as tall as a ten storey building and the turbine will be perhaps 500m away from the boiler. The length of pipe could quite easily be 1km between the two. When you consider the amount of the expansion mentioned above, the whole pipe will grow in length by 7.5m.

Peel away the insulation around the pipe when it is hot and you will actually see the pipe glowing a dull cherry red - at this temperature the metal from which the pipe is made becomes like plasticine. If it is not supported correctly it will sag and deform; this will cause problems to the subsequent operation of the plant. Drainage slopes will become disturbed, excessive forces will be transferred to the boiler and turbine connections and eventually the power station will not be able to operate.

An example of what can go wrong under such situations occurred at Money Point power station in Ireland some years ago. Steam was released into pipe work where a pool of water had gathered; the pressure of the steam forced the water through the pipe causing severe damage to the pipe, the supports and even the building structure. A very costly repair followed!


WHAT IS THE MAXIMUM LOAD FOR VARIABLE AND CONSTANT SUPPORTS DURING HYDROSTATIC TESTING?
Details of allowable load for hydrostatic test are as follows:
For constant effort supports: 2 x support load.
For variable effort supports: 2 x maximum load for the spring.

If the hydrostatic test load is greater than this, this must be specified on the enquiry and order. PSL will then design special spring housings to accommodate the high test load. Alternatively, additional temporary supports are sometimes used during hydrotest.


IF THE DESIGN TEMPERATURE IS 546 °C HOW CAN YOUR PIOPE CLAMP REFERENCE PC3-300-5-490 IN A387 GRADE 12 BE USED?
Both grade 12 and grade 22 materials are suitable for use up to 649 °C (1200 °F). Above approx. 510 °C the allowable stress for grade 22 material is higher than that for grade 12 material, so when designing a clamp for 546 °C the material section size will be heavier if it is designed using grade 12 material than if it is designed using grade 22 material.

In producing the PSL catalogue for alloy pipe clamps, we designed clamps which achieve the standard load group load capacities at four temperatures, 490, 530, 560 and 600 °C. We also calculated the actual load capacities for all of these clamps in the range 350 to 600 °C.
When selecting an alloy steel clamp, it is necessary to choose a clamp whose load capacity at pipe temperature exceeds the applied load at temperature. The part numbering merely indicates what design temperature was used to achieve the standard load group load capacity at this temperature. Clamps designated ... - 490 can be used at 600 °C and clamps designated ... - 600 can be used at 410 °C.

It is only necessary to ensure that the applied load at temperature is less than the load capacity at temperature. The last three digits of the part number do not imply a maximum allowable temperature for the component. Allowable load capacities for pipe clamps at temperature are clearly shown in the PSG catalogue. Our selections combine 'fitness for purpose' and 'most economic choice'.


FURTHER QUESTIONS & ANSWERS ABOUT PSG SOFTWARE AND SUPPORTS
Question:  There is an option to export a 3D DXF image to 3D CAD programs. Would it be possible to import a support assembly from compatible files by using SupportModeler? We would need to import the complete support in one piece and not component by component.
Answer: If you are using PDS with SupportModeler, we have an interface where pipe data is read from the PDS model and PSDesigner passes data back to SupportModeler which creates the support in PDS from the SupportModeler PSL parametric library. This interface is available to download from the website.
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Question: Elevations are included as input data when we model hanger systems in PSDesigner. Our problem is that we are not obtaining those elevations in our detail hanger drawings ( PDF or DXF files). Could you please provide us support or guidance about this problem?
Answer: In PSDesigner, click “Properties” button, “General” Tab and select “Show Elevation”.
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Question:  Does your PSDesigner provide information or warnings about allowed minimum height in hanger assemblies?
Answer: It doesn’t do this at present. This is one área we are now working on.
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Question:  We have tried to model constant load springs in SupportModeler with the PSL library. Springs modelled appear with no realistic dimensions (Dimensions modelled do not correspond with dimensions in PSL Catalogue). What could this be due to?
Answer: The constant support is modelled parametrically in SupportModeler. It is necessary to specify the correct parameters. If you use the SupportModeler-PSDesigner interface, the correct parameters are specified automatically.
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Question: Detailed spring drawings are produced including pipe clamp bases by default in PSDesigner. We are going to purchase springs without pipe clamp bases in general. How can we indicate this in purchasing drawings?
Answer: If you are using stand-alone PSDesigner, you just specify pipe size as zero. If you are using the SupportModeler-PSDesigner link, you will need to draw the assembly including the clamp base initially, then delete the clamp base from PDS.
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Question: Usually spring loads can be increased up to 2.5 times during hydrostatic test. What additional load can be increased in PSL springs?
Answer: The standard springs are suitable for 2 x design load (constant supports) and 2 x máximum load (variable supports). Greater test loading will require modified designs.
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Question: We have found in your catalogue that the height of variable load springs changes when installed load is also altered. What possibility of adjustment is allowed when the spring has already been calibrated?
Answer:  Suspended-type springs have +/- 75mm length adjustment. Base-mounted (pusher) springs have +/-25mm height adjustment.
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Question: How can we specify V4 and V5 springs in PSDesigner?
Answer: The V4 & V5 springs are recent additions to the product range. They will be added to PSDesigner in due course.
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Question: With regard to sliding plates, Easislide bearings are designed to withstand a wide range of enviromental conditions (in the catalogue it is indicated that plates are capable of withstand temperatures from minus 200ºC to plus 400ºC). The selection charts show the possibility of selecting an Easislide bearing by size of plate and load. We have noted that in most of the cases your recomendations about loads are imposed at 25ºC. How can we select a sliding plate in case of different temperatures?
Answer: For ES07 to ES12 bearings at higher temperatures, you need to downrate the load capacity by using the graph showing máximum bearing pressure on P136 of the catalogue.
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Question: PSL  can supply non-standard designs to allow movements greater than Range 3 (37.5 mm). For our project sliding plates are required for shoes with movements greater than 200 mm. We would appreciate it if you could inform us about the way to select sliding  plates in cases of high temperatures and high movements.  We are going to use standard shoes and they are different from PSL pipe clamp bases with high movements. Would it be possible to request sliding plates with different dimensions according to different requirements?
Answer: This extract is taken from the PSG catalogue:
Design for Large Movement
We can supply non-standard designs of types ES07 to ES12 to allow for movements greater than Range 3 (+/-37.5mm).
For pipework applications with very large horizontal movements, the standard design of PTFE / stainless steel bearing with the large upper plate may not be practical. Large lateral movement could cause the pipe shoe to twist around the pipe, or a twisting moment can be applied to the pipe which is also undesirable. In these circumstances, it may be preferable to install the bearing with the smaller PTFE-bearing plate at the top. PTFE on PTFE designs with overlapping strips of PTFE can also be considered. Note that an increased coefficient of friction will apply for PTFE-on-PTFE bearings and a lower bearing pressure should be used.