[Fwd: Re: [STM] Re: Steam line intermediate anchor]

The opening statement was…

   "We have a 16", 60 psig steam line constructed in 1955, and it was placed in a chase type system with slip style expansion joints in concrete manholes to compensate for thermal expansion. According to the
original design documents there were no intermediate anchors installed
on runs of steam piping where expansion joints are on either end of the
run. Not having an intermediate anchor would allow the steam piping to
grow in the path of least resistance and if the expansion joint travel
was not oversized enough to compensate for the growth of the entire run
of piping, the piping would then bump off of the limit stops inside one
expansion joint before the piping grew in the other direction. I may have this situation as when this line was shut down and I was inspecting
for an expansion joint replacement, I noticed that an expansion joint had only contracted about a half an inch, where it should have moved at
least a couple of inches. This would indicate either a broken intermediate anchor or a complete lack thereof, from the initial design.
I was just curious if any one else had encountered this type of design
on older lines? I will be doing an exploratory dig at the mid point of
this line coupled with some abatement to search for a broken anchor, or
if there is not an anchor, establish one after I make sure my piping is
not offset too far one direction or the other."

I looked over your scanned drawings which do not seem to show a centered axial and lateral restraint (I hate throwing about the word anchor loosely. An anchor is a restraint which prevents all linear and rotational movements. People who use the word Anchor really mean in 99.9% of the cases linear restraints it doesn't usually matter if some slight rotation occurs).

Lacking an intermediate restraint the pipe as you have stated will grow whichever way is easier. I noticed the pipe was supported on pipe rolls… These rolls usually roll only once… off the back of truck into the dirt and into the installation where they don't roll. So one or more of these on one end or the other may be more seized… or the line may actually be pinching the side of a roller.

In any case if you want to make this foggy situation a bit better I suggest that you pull the lines back so that the gaps are centered in your slide joints (repack and recondition them or replace them)… then put an intermediate mid pint linear restraint on each line. I would design it to overcome the frictional load of ½ the system being pushed against the rolls with the rolls not rolling lets say mu=0.4. That should give the support adequate strength.

Best Regards,
John C. Luf Received on Tue Jun 28 10:24:00 2005