On large process pipes and tanks, a pH sensor cannot simply be unscrewed for cleaning. Removing it from a threaded fitting means isolating and draining the line, which on a continuous process in a Malaysian chemical plant, power station or water treatment facility can mean lost production. That is why many sites install hot-tap retractable sensors such as the ABB TB557 or TBX557, which can be inserted and withdrawn through a ball valve while the process keeps running.
When a TB557 needs replacing, the hot-tap hardware already installed on the pipe is the most valuable part of the installation. The LECOL B75 hot-tap insertion pH sensor is LECOL’s equivalent model for this installation type. This article explains how a hot-tap sensor differs from a normal pH sensor, how the B75 is built, and what to check when replacing an ABB TB557 in Malaysia.
The short answer is this. A normal pH sensor is fixed in place and needs a process shutdown to remove, and its liquid or gel reference is easily poisoned in aggressive service. The LECOL B75 combines a hot-tap design, which allows safe insertion and retraction through a 1-1/4 inch ball valve without stopping the process, with LECOL’s patented solid-state ION BARRIER reference and a large-area junction. It is the LECOL counterpart to the ABB TB557, intended to suit the same hot-tap installations.
Why hot-tap sensors exist
A normal pH sensor installed in a pipe tee or flow cell is easy to fit, but every cleaning, calibration or replacement requires the line to be isolated. On a large pipe without a sample line, or on the side of a process tank, that is often not practical.
A hot-tap sensor solves this with three components: a full-port ball valve fitted to the process, a compression fitting that seals around a long sensor sleeve, and the sensor itself at the end of that sleeve. To remove the sensor, the operator loosens the compression fitting, withdraws the sleeve past the valve, closes the valve, and only then removes the sensor. The process never has to stop.
The design places extra demands on the sensor. It must seal reliably against process pressure at the compression fitting, it must be retained safely during withdrawal, and because it is removed less often than a normal sensor, it must hold its calibration for longer between visits.
How the LECOL B75 differs from a normal pH sensor
Hot-tap insertion with a safety tip. The B75 installs through a 1-1/4 inch full-port ball valve and can be inserted or retracted without process shutdown. A flared safety tip prevents the sensor from being ejected by process pressure during removal, which is a real hazard with pressurised lines.
ION BARRIER solid-state reference. Instead of a liquid or gel potassium chloride reference, the B75 uses LECOL’s patented multi-layer solid-state reference. Process sample passes through a wood-cell filter and then the ION BARRIER, a matrix of ionic pathways that slows the movement of aggressive ions towards the silver/silver chloride element. Because hot-tap sensors are serviced less often, slower poisoning translates directly into longer intervals between interventions.
Large-area junction. The junction is available in porous PTFE for general service, or wood for oily and hydrocarbon-fouling streams, both with a much larger contact area than the small ceramic junction of a normal sensor.
Materials for the process. The inner sensor body is PVDF. The outer sleeve is 316L stainless steel or Hastelloy C, the compression fitting is available in 316L, Hastelloy C or titanium, and O-rings are Viton as standard or FFKM for aggressive chemistry and high temperatures.
Sleeve lengths to suit the pipe. Standard sleeve length is 16 inches, with 24, 32 and 36 inch options and custom lengths, so the glass can be positioned correctly in large pipes and tanks.
Glass and temperature options. The measuring electrode can be hydrofluoric acid resistant, coating resistant hemispherical or flat glass, low temperature, high temperature (15 to 135°C, tolerating 140°C temporarily) or platinum ORP, with optional PT100 or PT1000 temperature compensation. The B75 is rated to 10 kg/cm2 at 70°C and 2.8 kg/cm2 at 135°C.
| Feature | Normal pH sensor | LECOL B75 hot-tap |
|---|---|---|
| Removal | Requires line isolation and draining | Retract through ball valve while process runs |
| Reference | Liquid or gel KCl | Solid-state ION BARRIER, patented |
| Junction | Small ceramic pin | Large-area PTFE or wood |
| Safety on removal | Not applicable | Flared safety tip prevents ejection |
| Wetted hardware | Usually plastic body only | 316L SS or Hastelloy C sleeve; 316L, Hastelloy C or titanium fitting |
| Insertion depth | Fixed, short | 16 to 36 inch sleeves or custom |
Replacing an ABB TB557 or TBX557 with the LECOL B75
The ABB TB557 is a hot-tap retractable industrial pH/ORP sensor, and LECOL identifies the B75 as its equivalent. Because the ball valve and process connection are already in place on most TB557 installations in Malaysia, the goal of a replacement is to reuse that hardware. The B75 is supplied with a 1-1/4 inch NPT isolation valve option, including reducing bushings for 1 inch and 1-1/2 inch connections, which covers the common installation sizes.
Before ordering, confirm the following against the existing TB557 installation. Autoflo checks these as part of supply:
Valve size and thread. Confirm the existing ball valve size and thread so the B75 compression fitting and sleeve pass through it correctly.
Sleeve length. Measure the distance from the outside of the valve to the required sensing position in the pipe. Too short and the glass sits in a dead zone near the wall; too long and it may hit the far side of the pipe.
Materials. Match the sleeve, compression fitting and O-ring materials to the process chemistry. Hastelloy C and FFKM are worth considering for chloride-rich, strongly acidic or high temperature service.
Pressure and temperature. Check the process against the B75 rating of 10 kg/cm2 at 70°C and 2.8 kg/cm2 at 135°C, and remember that retraction is always done at the lowest practical pressure.
Analyser connection. Confirm the temperature element (PT100 or PT1000) and any solution ground connection required by your analyser, and select a cable length to suit, from 3 metres up to 30 metres or custom.
Where the B75 fits in Malaysian industry
The B75 is designed for recirculation piping, large pipes without sample lines, tank side mounting and cooling water circulation, and for demanding service in chemical reactors, scrubbers and high-pressure pipelines. In Malaysia, these installations are common in petrochemical and chemical plants, power stations, large cooling water systems and central water and wastewater treatment facilities, where shutting down a line for sensor maintenance carries a real production cost.
Getting the most from a hot-tap installation
The advantage of a hot-tap sensor is lost if operators avoid retracting it because the procedure feels risky. A short, written retraction procedure at the sensor location, covering pressure checks, the order of loosening the fitting and closing the valve, and the safe position of the operator, makes maintenance routine rather than exceptional. Combined with a reference that resists poisoning, this is what keeps a hot-tap pH measurement accurate over the long periods between visits.
Autoflo Technology is the authorised distributor of LECOL pH and ORP sensors in Malaysia. If you are replacing an ABB TB557 or TBX557 hot-tap sensor in Malaysia, send us the existing model code and valve details and we will confirm the matching LECOL B75 configuration. Contact us at info@autoflotechnology.com.
Other ABB TB5 series replacements in Malaysia
Replacing a different TB5 model? See our guides to the ABB TB556 pH sensor and the LECOL B65, the ABB TB564 high-pressure hot-tap pH sensor and the LECOL B86, and the ABB TB567 high-pressure pH sensor and the LECOL B85.
ABB, TB557 and TBX557 are trademarks or product designations of ABB. They are referred to here only to identify compatible installations. Autoflo Technology and LECOL are not affiliated with or endorsed by ABB.