grade; however, for many reasons this is not possible.Trenched or buried piping should be avoided but, sometimes,is unavoidable. Pipe racks at higher elevations, usingsupports, are preferred.. Pipe racks may contain one, two, or more layers of pipework;however, triple-layer pipe racks should be limited to veryshort runs.. Run piping external to the process area at grade on sleepersgenerally 300 mm high. Pipe ways at grade are cheaper butmore liable to interfere with access.Locate the largest bore and the heaviest piping as close tostanchions as possible.Lines requiring a constant fall (relief headers) can be run oncantilevers from pipe-rack stanchions or on verticalextensions to pipe-track stanchions.Run the hot line requiring expansion loops on the outsideedge of pipe way to permit loops to have greatest width overthe pipe way and facilitate nesting.Takeoff elevations from pipe ways should be at a constantelevation, consistent with the range of pipe sizes involved.Change elevation whenever banks of pipes, either on pipeways at grade or at higher elevations on pipe racks, changedirection.Elevations to the underside of pipe racks should be theminimum for operation and mobile maintenance equipmentand consistent with allowable clearances.Open pipe trenches may be used between plants where thereis no risk of flammable vapors collecting.It sometimes is convenient to run open trenches alongsideroadways. (Soil from the trench can be used to build up theroad.)Where a pipe way or road changes from a parallel direction,the pipe generally is run beneath the road.Occasionally, it is permissible to run pipes in trenches toovercome a difficult piping problem. Such trenches should beof concrete, drained, and covered.Altltough ttcnched piping is to be avoided, dtrc to thct'xPt'rtst'atttl llaziuds its:iociatc(l with ol)cn tlr.'rrcltt's, JriPirrl;