This article provides the necessary brief information to assist the site engineers/field engineers/ construction engineers during the first installation and connection of piping with the relevant rotating machinery.
During operations, the equipment should be preserved and protected in compliance with the supplier’s procedure. In order to prevent any grit and foreign matters from entering, make sure that all paths and openings are properly blocked up and sealed. Antidust covers should remain installed until the final alignment is completed.
Once the skid or module has been levelled and grouted, the machines should be aligned according to specification, after this operation they will be available for piping installation (including instrumentation and electrical connection piping).
Machine leg anchor bolts should be tightened and the relevant washer (Belleville washer) should be locked in order to anchor the machine to the skid. The axial and transversal keys should be fixed in position, but no fixing welding or pinning shall be carried out.
Do not perform any welding operations on pipes connected to the foundation, machinery base-plates or the machinery itself, without the proper direct grounding connection with the welding transformer. In order to avoid any damages on the machinery supports caused by dispersing current, grounding cables should not be connected to any part of the rotating machinery (base-plate, pedestal, control circuit apparatus, etc.).
During piping construction, pipes can be temporarily connected to the machine. Pipes should be properly supported (with temporary supports) in order to avoid stress or interactions during the alignment operations. While those activities are carried out the machine must be firmly locked in position.
Before connecting pipes to the machine and checking final alignment, all operations on piping systems have to be completed. Including the following activities: pressure tests, washing and air flushing and permanent support installation (fixed, sliding and elastic supports). While those operations are carried out, piping has to remain always disconnected and insulated from the machine.
Pipes have to be connected to permanent supports in order to be installed in the correct final position so that elastic supports are pre-loaded at the required load (cold position) with assembled pins.
Pipes should be sustained by supports so that connection flanges are within the coupling tolerances.
If the customer is in charge of piping supply, he has to provide all the relevant information.
Flange fitting tolerances between machine and piping
Before fixing the piping flanges on the machine flanges, planes have to be aligned in parallel as shown in the Figure 1.
The difference between the maximum and the minimum distance will be a “T” misalignment value, to be checked with the acceptance criteria sheet (see Figure 1). After each adjustment, please check and record the measurements until an acceptable alignment is reached.
Check the gasket type, material and dimension. The distance between flanges should be just enough to insert the gasket by sliding it inside without causing any damage on it and on the flange planes.
Check the dimensions of flange hold down bolts and align the relevant holes. Flange bolt holes have to be aligned within a maximum 3 mm offset, and in any case, when flanges are coupled, hold down bolts should freely slide without any interference through holes.
Make a visual inspection of the coupled flanges. Surfaces should generally be in good condition; in particular, scratches in radial direction and oxidation are not admitted. As regards flange condition acceptance criteria and detailed prescriptions, please refer to ASME B16.47 and B16.5 procedures.
Pipes should not be firmly connected to the machine until final piping supports are installed. In order to avoid any undue stress, piping installation should never start by the machine flange side.
Elastic Support Check
Once the machine flange and piping flanges tolerances have been checked, release the elastic supports by removing the locking pins, and make sure pipes remain in position (free to spring around the fixed position).
While piping machine tightening activities are carried out, install dial gages on the machine legs in order to monitor any abrupt displacement and the alignment equipment too.
Starting from one of the pipes to be connected, tighten the four tie rods (staggered tightening) between the machine flange and the relevant piping flange, until an intermediate torque is reached (70%-80% of the torque value indicated in the specification).
Remark: All operations executed until now have to be performed with the machine fixed on the base-plate, in order to keep the required position according to the alignment specification.
Intermediate Alignment Check
Release the machine, by unscrewing the fixing screws of the machine axial keys, and by releasing washers (or Belleville washer). Check for any dial gage range. Verify that the alignment has not changed.
– In case of small alignment variations, some adjustments are admitted only on the horizontal plane. If during the alignment correction some elastic responses (spring effect) are sensed by the dial gages, it will not be possible to proceed with the final tightening, and piping restoration will be necessary.
– In case of considerable alignment variations it will not be possible proceed with the final tightening, and piping restoration will be necessary.
Piping restoration operations shall consist in displacing pipes by acting on their supports, in order to eliminate a forced assembling with the machine (cause of misalignment). If this operation is be enough, cutting and welding of the piping will be necessary in order to correct its geometry.
Perform the same Pre-Tightening operations and checks, verify the Intermediate Alignment restoration for all remaining pipes to be connected, making sure the machine is always fixed on the skid during pre-tightening, and do release it before performing the alignment check.
After reaching the pre-tightened piping condition (70%-80%) and machine aligned condition, fix again the machine on the skid (by tightening the axial keys and the washers or Belleville washers). Proceed by tightening rods at the final torque values.
After the final tightening, release the machine; verify the alignment, the DBSE between the machines you are working on and the adjacent machines.
With the aligned machine and all pipes tightened at the required torque values, proceed with the final arrangement by fixing machine and/to the skid, as follows:
- – Fix the axial keys, with the required fixing screws, and furthermore (if possible /if foreseen) with welding points.
- – Fix in the required position the machine legs to the base-plate (or to the proper supports on the base plate) by using the required pins.
- – If calibrated washes are provided, make corrections in order to obtain the required clearance.
Final Alignment Check:
After the final tightening, please verify the Alignment.
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