Page 173 - Machinery Component Maintenance

Process Machinerx Piping 155

If leakage persists, piping support and flexibility must be examined.
It may be necessary to revise the support system or install spring
hangers to lower bending moments.
If leakage occurs during rainstorms, it will be necessary to install
sheet metal rain shields, which may cover the top 180" of the flange,
to prevent such leakage. These should be located about four inches
away from the flange surface and should have sufficient width to
cover the bolts plus two inches on each side.
If leakage occurs during sudden changes in process temperatures, ex-
amine the process sequence to determine if steps can be taken to min-
imize rapid heat-up or cooling of lines. It may only be necessary to
open a valve more slowly.

Recommendations for the Installation, Fabrication,
Testing and Cleaning of Air, Gas or Steam Piping*

The importance of starting any compressor with clean piping, particu-
larly on the intake to any cylinder, cannot be over-emphasized. This is
particularly important with multi-stage high-pressure compressors where
special metallic packing is required and parts are much more expensive
than in a low-pressure compressor. Any dirt, rust, welding beads or scale
carried into the compressor will cause scored packing rings, piston rods,
cylinder bores, and pitted, leaky valves.
It is important that the piping be fabricated with sufficient flange joints
so that it can be dismantled easily for cleaning and testing. It is far better
to clean and test piping in sections before actual erection than after it is in
place.
If it is necessary to conduct the final test when the piping is in position,
care should be taken to provide vents at the high spots so that air or gas
will not be trapped in the piping. Make provision for complete drainage
after the test is completed. These connections should be planned in ad-
vance.
When piping is cleaned in sections before erection, it is possible to do a
thorough job of eliminating all acid. This is difficult to do with piping
erected and in position, because carry-over of acid into the cylinders is
almost certain to occur when the machine is started. This can cause ex-
tensive damage.
The use of chill-rings for butt welds in piping is recommended. This
prevents welding beads from getting into the pipe to carry through, not
only on the original starting, but later on during operation.

Rcfcr to appendices at the end of this chapter for typical checklists.