Wednesday, September 12, 2012

NEW BLOG - Why Use Regulated Outlet Points?

INTRODUCTION

Outlet points on a pipeline installation, that use flowmeters for argon and argon/CO2 mixtures should always be regulated at each outlet to ensure the correct flow rate.

The readings shown on flowmeters fitted directly to a pipeline cannot be guaranteed as being accurate. When multiple units are in use, the demand on the pipeline increases significantly and adversely affects the flow to each machine. This leads to poor quality welds and porosity. Operators tend to try to compensate for this by either turning up the pipeline pressure (which makes for incorrect readings on the flowmeters), or increase the outlet flow on the flowmeter. Neither of these options improves the situation, the weld or decreases gas consumption.

THE PROBLEM WITH USING FLOWMETERS ONLY

All flowmeters are calibrated to be accurate at a nominated inlet pressure. This may vary from brand to brand, but generally it is 250 kPa to 350 kPa. At this nominated inlet pressure the reading in L/min from the flowmeter will be accurate. This is critical in the welding process as the welding procedures for the type of welding being done will nominate the flow rate of the shielding gas. Too much flow causes a venturi effect at the nozzle drawing in air causing porosity, too little shielding gas can cause porosity due to contamination from the atmosphere.

Each time gas flow is actuated there is also a huge surge of gas if the flowmeter is not regulated. Installing a regulated flowmeter helps to dramatically reduce this wasted gas.

CASE STUDY 1

A pipeline installation where there are 10 outlets using 10 mm pipe and outlets fitted with flowmeters only.  The rated inlet pressure for the flowmeters to be accurate is 300 kPa, therefore the pipeline pressure is set at 300 kPa. The required flow rate for the shielding gas is 15 L/min.

When one flowmeter only is operating the reading will be accurate, however, when multiple flowmeters are operating there will be a pressure drop over the line and as a result, the inlet pressure to each flowmeter will also drop.  This constant change in inlet pressure to the flowmeters as other flowmeters connected to the line are turned on and off, causes inaccurate and fluctuating readings on the flowmeters in use and is a major cause of weld defects.

Depending on the number of flowmeters in use, flow rates could drop as low as 50% (or more) of the required rate. To compensate for this, the operators increase the line pressure and crank up the flowmeter to 30-40 L/min rendering all readings on the flowmeters useless and making it nearly impossible to obtain an accurate and consistant flow rate from the flowmeter required for a quality weld.

HOW REGULATED OUTLET POINTS WORK

When you install regulated outlet points, you can run the pipeline at a higher pressure. The regulators at each outlet then lower the pressure to the correct inlet pressure of the flowmeter, ensuring no pressure drop, accurate flow rates and accurate readings at each outlet point.

It is acceptable to run two flowmeters from each regulated outlet as there will be no pressure drop or reading fluctuation. Because there is a regulator at each outlet point, the gas surge every time the welding gun is actuated is minimised and the gas consumption drops dramatically.

CASE STUDY 2

A pipeline installation where there are 10 outlets using 10 mm pipe and outlets fitted with regulators and flowmeters.  The rated inlet pressure for the flowmeters to be accurate is 300 kPa, therefore the regulators at each outlet are pre-set at 300 kPa.  The pipeline pressure is set at 600 kPa to allow for pressure drop when multiple units are drawing gas.  The required flow rate for the shielding gas is 15 L/min.

When one flowmeter only is operating the reading will be accurate, when multiple flowmeters are operating there will be no change at each flowmeter and the inlet pressure to each flowmeter will not drop and will not vary, ensuring accurate readings on the flowmeters and the correct supply of shielding gas to each application. The welds are of better quality and gas usage is economical because it is controlled.

NOTE: The general principles of using regulated flowmeters to achieve the results mentioned is sound, however results will vary from case to case and site to site, depending on pipe sizes, gas equipment used, welding equipment used, number of outlet points and length of hoses from the outlet point to each machine. Please contact Tesuco for any advice regarding regulated outlet points and achieving the best results.

Tesuco can supply a number of solutions for regulated outlet points for welding applications, here are some links to a number of products available for this purpose:

Twin Outlet Argon and Argon Mixed Gas Systems

Regulated Flowmeters and Wall Mounted Systems

Flowmeters and Flow Restrictors

Mark Stadtmiller

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