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 from 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.