Design, Butt Weld Ends

92
Reheater Isolating Device
Sizes 16”– 36”
ASME B16.34
Introduction
Hundreds of thousands of pounds per day are lost
whenever a power plant closes!
Repairs of installation facilities are frequently a part of a
planned programme of maintenance. The downtime
cost is figured into the operating budget. Even so, any
innovation which can save time will also save significant
amounts of money.
A chief method for determining the effectiveness of the
repairs done on plant pipelines is hydrostatic testing. In
one area of a plant, the reheat tubes located in the
boiler and the pipelines adjacent to the boiler, testing
has been a time consuming and costly problem.
Isolation of the tubes from the pipeline has been done
by mechanically forcing a blind flange between two
flanges welded into the line. This procedure is slow,
difficult, awkward and expensive.
Isolating of the hot reheat section has been traditionally
achieved by closing the turbine intercept valve.
However, turbine manufacturers and utilities have
expressed some concern in relying solely on the turbine
intercept valve as a stop valve.
The Dewrance Reheater Isolating Device, (R.H.I.D.),
however, allows hydrostatic testing to be conducted
easily and efficiently on both the cold and hot reheat
lines. On the cold reheat line, from the high pressure
turbine, temperatures average 600-700 ˚F and pressures
range from 600-700 psi. The R.H.I.D. has an ASME 500
Intermediate rating and cast carbon steel
(A.216 Gr. WCB) body material to satisfy pressure
temperature requirements of the cold reheat line.
On the reheat line, from the Reheater Section of the
boiler, temperatures range trom 900-1025 ˚F and
pressures from 500 to 1200 psi. ASME Class 900# R.H.I.D.
with cast alloy steel (A.217 Gr. WC9) body material is
utilized on the hot reheat lines.
The R.H.I.D. also reduces the possibility of damaging the
intercept valve by providing a reliable seal in front of
the turbine intercept valve.
After installation the R.H.I.D. is merely a conduit and
during normal operation it is open and free from any
component parts.
When hydrostatic testing is to be done the system can
be isolated by merely placing a closure in the path of
the flow. This is accomplished by removing the bolted
pressure seal joint from the R.H.I.D. fitting the Isolating
Closure into position and then resetting the pressure
seal.
The R.H.I.D. is uniquely designed to take advantage of
two different forces for establishing seals. During
regular service the Body/Bonnet Joint is mechanically
preloaded prior to operation. When steam passes
through the line it reinforces the mechanical seal with
pressure. The Isolating Closure used during hydrostatic
testing is similar; it is mechanically preloaded before
testing and water pressure acting on the closure
upgrades the seal.