Structural Design for Pipework
When pipework gives trouble, the cause is often the structure holding it up (the rack, the supports, the pipe bridge across the road), because it was never designed for everything acting on it. Structural design for pipework covers that structure and the supports and restraints that attach the pipe to it, so the pipe stays where it should and only moves where it’s meant to over its service life. At Element Mechancial Design we do this work for industrial and mining sites, backed by finite element analysis (FEA) where the loads or geometry warrant it. It sits alongside the design and FEA work our mechanical team does on plant, equipment and load-bearing structures.
What structural design for pipework involves
Most of the work is in the load paths. An operating line is far heavier than it looks once you add the contents, insulation, valves and fittings. And all of that weight has to travel through the supports and into the foundations. And it has to do all that without overloading anything on the way. For gas and vapour lines the hydrostatic test (line full of water) can be the governing case. On top of self-weight come thermal expansion as lines heat and cool. Plus wind on exposed racks and potential earthquake actions. Also there’s friction at sliding supports. And occasional loads such as water hammer and relief valve thrust. And the restraint reactions the piping transfers into its supports.
We design the steelwork to AS 4100, with actions from AS/NZS 1170.1, AS/NZS 1170.2 and AS 1170.4 combined to AS/NZS 1170.0. We also work with the piping designer (AS 4041 or ASME B31.3, depending on the project) so the structural and piping designs agree on where the loads go. If the supports don’t allow for the loads and the expansion, you end up with cracked welds, leaking flanges, sagging lines and unplanned shutdowns.
It’s common to size the pipe and treat the structure under it as an afterthought. A full line is a serious load, and it moves as it heats up and cools down. If the supports don’t allow for that, the pipe finds its own way to move, and that usually shows up as an overloaded equipment nozzle or a pipe shoe that’s walked off its support.
Daniel Berti, Mechanical Engineering Team Leader – Element Mechanical Design
Industrial pipework
Industrial plants run pipework for process fluids, steam, compressed air, water and chemicals. Unfortunately, it’s often in tight, congested plant rooms and yards. The structural challenge is usually access and coordination. Racks and supports have to fit around equipment, carry the loads and still leave room for maintenance. We design pipe racks, T-supports, sleepers, anchors and guides, and the bracing that keeps the structure stable. We detail the supports so the piping can expand and contract without dragging the structure with it.
Mining pipework
Mining sites push pipework hard. Slurry, dewatering, process water, tailings and reagent lines run long distances across sites that are remote, dusty and often cyclone-exposed. The structural design has to account for cyclonic wind (Regions C and D under AS/NZS 1170.2), the extra weight of dense slurry (and of a line that’s sanded up with settled solids after a shutdown). Add the fact that a failure on a remote site is expensive and slow to fix. We design the racks, pipe bridges and supports to take those loads. We also lay them out so crews can safely get to the wear sections and maintenance points.
Related blog: Cyclonic Wind Loading for Fixed Plant in the Pilbara
Industrial pipework
Industrial plants run pipework for process fluids, steam, compressed air, water and chemicals, often in tight, congested plant rooms and yards. The structural challenge is usually access and coordination. Racks and supports have to fit around equipment, carry the loads and still leave room for maintenance. We design pipe racks, T-supports, sleepers, anchors and guides, and the bracing that keeps the structure stable. We detail the supports so the piping can expand and contract without dragging the structure with it.
Mining pipework
Mining sites push pipework hard. Slurry, dewatering, process water, tailings and reagent lines run long distances across sites that are remote, dusty and often cyclone-exposed. The structural design has to account for cyclonic wind (Regions C and D under AS/NZS 1170.2), the extra weight of dense slurry (and of a line that’s sanded up with settled solids after a shutdown), and the fact that a failure on a remote site is expensive and slow to fix. We design the racks, pipe bridges and supports to take those loads, and lay them out so crews can safely get to the wear sections and maintenance points.
High-temperature and hydrocarbon lines
Hot hydrocarbon lines are some of the hardest pipework to support. Large thermal movements and hazardous fluids mean the structural design and the pipe stress analysis have to be developed together. The supports have to allow for the growth (with spring supports where a line moves vertically) and sit where the pipe stress engineer needs them, so pipe stresses stay within the piping code allowables and nozzle loads stay within the equipment manufacturer’s or equipment standard’s limits. This is detailed, safety-critical work, and it needs the structural and pipe stress engineers working off the same loads, movements and support locations from the start.
A 50 m carbon steel run operating at 300°C grows by around 180 mm as it heats up. The structure has to let it move in the right directions and stop it in the others, and working out where to guide and where to restrain is where most of the design effort goes.
Daniel Berti, Mechanical Engineering Team Leader – Element Mechanical Design
FEA for the harder cases
Not every support needs detailed analysis, but the hard ones do. Where thermal movements and restraint loads are large, or where a connection, support or attachment falls outside the simple cases, we use FEA to check local stresses and deflections in the support steelwork under the governing load combinations before anything is built, rather than relying on a rule of thumb. The rack and bridge framing itself is designed and checked to AS 4100. We run FEA in-house, and it’s worth the time wherever the cost of getting it wrong is high.
Design documentation
We document the design basis, load cases and results so the work can be built and maintained. Every design comes with a report setting out the standards, loads and checks the structure was designed to, so it can be independently checked.
If you’ve got a pipework project (a new rack, an upgrade or a line that keeps giving you trouble), talk to Element Mechancial Design. We’ll tell you what the structure needs and design it to suit.