Honeywell STG73P SmartLine Flush Mount Pressure Transmitter

Honeywell STG73P SmartLine flush mount gauge pressure transmitter

The Honeywell STG73P is the flush-mount model of the SmartLine ST 700 range. Instead of a threaded or flanged connection, it slides into a 1 inch sleeve that has been welded into the pipe or vessel wall, and the diaphragm face is positioned flush with the inside surface. With no cavity or dead leg in front of the diaphragm, stock, slurry or fibrous liquid cannot pack in and plug the connection, and the unit can be pulled and replaced quickly. Seven Star LLC supplies the STG73P in Oman and the GCC as an independent supplier in Muscat.

Honeywell describes it as a gauge pressure transmitter with a Hastelloy C-276 diaphragm and a 316L stainless meter body, a single range of −14.7 to 100 psig, accuracy up to 0.065% of span (0.04% optional), stability up to 0.02% of URL per year for ten years and response as fast as 100 ms. Output is 4-20 mA with HART 7 or Honeywell DE.

Reading the STG73P model code

The STG73P has one measurement range in the selection guide, so the model is fixed and the choices that follow are the meter body (a single Hastelloy C-276 interface, silicone fill and the 1 inch slip-in connection with locking screw), approval, housing, output protocol, display, configuration and calibration, bracket and tag. The sleeve is referenced as optional in the ordering table.

STG73P technical specifications

How flush mounting works in practice

A conventional gauge transmitter takes its pressure through a threaded port or a short impulse line. In stock lines, black liquor, sludge, sewage or any liquid with solids, the port can fill with packed material and the reading freezes. The STG73P avoids that by placing the diaphragm in the same plane as the pipe wall, where the flow itself keeps it clean.

The sleeve is the permanent part. It is welded into the pipe once, and the transmitter slips in, seals with an O-ring and is locked with a bolt. Because the sleeve stays in the pipe, the transmitter can be replaced or sent for calibration quickly. The datasheet reminds you that the process interface may reach 95 °C, and that above 65 °C the allowed ambient temperature falls one degree for each degree of process rise.

The 100 psi limit is a real constraint. This is a low-pressure transmitter designed for head boxes, tanks and low-pressure process lines, and it should not be selected for pressure above the 100 psi MAWP.

STG73P within the SmartLine ST 700 range

If your application can use a threaded or flanged connection, other ST 700 models may be a better fit. The STD700 measures differential pressure, the STA700 absolute pressure, the STF700 level through a tank flange and the STR700 uses capillary seals for hot media. The STG73P shares electronics, displays and terminal blocks with those models, so a plant that already uses ST 700 transmitters needs no extra spare module types.

The datasheet lists these field-installable kits, which are the usual spares for the family:

STG73P selection and ordering checklist

• Confirm the process pressure is within −14.7 to 100 psig including surges, because the MAWP is 100 psi.
• Confirm that a 1 inch sleeve with locking arrangement is acceptable and decide whether the sleeve is supplied or already installed on site.
• Check the process temperature, with the 95 °C limit and the ambient derating above 65 °C.
• Check that Hastelloy C-276 and 316L stainless are compatible with the media and that Viton suits the seal service.
• Choose HART or DE protocol, plus display type, external buttons, housing material and conduit entry (1/2 NPT or M20).
• Select the hazardous area approval and any NACE, marine or SIL documentation needed.
• Specify calibration range and tag.

Installing and maintaining the STG73P

Welding the sleeve is the critical step. It must be aligned so that the diaphragm face ends flush with the inner wall, and the weld and surface must be inspected before the transmitter is inserted. Insert the transmitter with a clean O-ring, tighten the locking screw to the value in the manual, and then wire the loop. The user manual is listed as 34-ST-25-44, with the HART/DE communications manual 34-ST-25-47 and the safety manual 34-ST-25-37.

Calibration verification is recommended every two years, and the diagnostics report faults such as electronics failure, sensor over-temperature or an out-of-range variable. Because modules are replaceable, a site spare set of one HART or DE electronics module and one display covers most failures.

Typical STG73P applications in Oman and the GCC

Honeywell highlights head boxes in pulp and paper mills, but the same logic applies to other low-pressure services with solids or sticky media. In Oman and the GCC the likely duties are sewage and industrial wastewater lines, sludge and slurry feed in water treatment, food and beverage process lines, sugar and salt services, and low-pressure drain and circulation headers where a conventional port blocks.

Sun-exposed pipework in summer can push the process interface and the housing close to the limits, so check both numbers and select the stainless housing for corrosive coastal air.

Information to send with an STG73P RFQ

• Required range, normal and maximum pressure, and process medium including solids content.
• Process and ambient temperature range.
• Protocol, approvals, housing, display and whether the sleeve is needed.
• Quantity, tag numbers and delivery location in Oman or the GCC.

Documents and quotation

The manufacturer technical information sheet for the STG73P is attached on this page, with dimensions and the selection guide. Read it together with your piping drawings and welding procedure.

Send the model and process data and Seven Star LLC will quote against it. Delivery time and certificates are confirmed in the quotation.