March 18th, 2010
Avoiding leaky flanges is paramount to safety at any industrial plant. Traditional ANSI flanges have been used for decades, and are still the most common choice for plant components at petrochemical plants. However, they are prone to leakage – something which needs to be addressed.
A number of improvements have been made to pipe fittings in recent years. For example, the new pressure connections, such as those we supply at Chemipetro, practically guarantee a leak-free performance. However, flange designs, for all their variety, have remained resolutely traditional. Their tendency to leak has been improved by modern technology, but not eliminated.
Conventional ANSI flanges are fitted by bolting two faces together, compressing a gasket and creating a seal. Integrity of the joint, and loading on the bolt, largely depends on the torque applied to the bolt when it is tightened.
The torques applied to pipe flanges are very specific. Therefore the proper procedures must be followed in order to avoid under or over-tightening and gasket leakage. However, even if the flanges are tightened exactly to industrial specifications, factors such as thermal expansion, internal pressures and fluctuating loads can cause movement between the flange faces.
The design of ANSI flanges means 50% of the bolt load is needed to compress the gasket, leaving only 50% to hold the pressure. Sudden, unexpected surges in line pressure, especially, can force the flange faces apart, placing stress on the bolts and creating an inefficient seal. Essentially, then, pipe flanges are inefficient.
Recent developments include patented compact flanges and API flanges. The latter withstand much higher pressures than traditional ANSI fittings.
Tags: ANSI flanges, Flanges, Pipe Fittings, Pipe Flanges
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March 10th, 2010
Industrial flanges and pipe fittings comply with standard dimensions – ANSI, API etc. This means companies like us at Chemipetro can easily supply flanges to companies across the world, and industrial plants can run with quiet efficiency – so long as the components are made to set standards of compatibility.
Industrial pipe flanges are used in many important areas, apart from the petrochemical industry. One in particular, the shipbuilding industry, shows the importance of installing compatible pipe fittings.
Modern shipbuilding is done in “blocks,” outsourcing different parts of the operation to different companies. Standardised systems of measurement are used, making ordering of stock quick and economical – so long as the same standards are applied across the entire outsourcing network.
This once wasn’t the case in the US Navy. A 1990 National Shipbuilding Research Program paper described how US ships installed a combination of pipe flanges – often in the same system. Commercial (ANSI) and Navy pipe flanges (Mil-Spec) were almost identical in terms of pipe sizes, pressure ratings, alloys etc. However, their physical dimensions – thickness, diameter bolt holes etc – made them totally incompatible with each other. The valves, pumps etc using those flanges were likewise unique.
This led to confusion for the installers, logistics and operations staff. It also meant very large ship stores, as the only answer was to provision two flange systems on each ship. The NSRP saw that non-compatibility was a serious problem, and streamlined the system by eliminating either Navy or ANSI flanges to create a standardised protocol. But until then, the costs – not to mention wasted man hours – were crippling.
Tags: ANSI flanges, Flanges, Pipe Fittings, Pipe Flanges
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