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.
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!
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.
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.
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.