TPi May 2016

Pipe flanges and tubesheet flanges for shell and tube heat exchangers By Andrew Johnson, business development manager, Alexander Comley Ltd, UK

dimensions that are standardised to a given/the given standard, ie all AFNOR/ASME/BS etc function dimensionally with others to the same standard – they are functional to one another. However, each of these dimensional global standards have nuances that mean they are not always functional with each other. For example, an AFNOR flange may not mate against a BS flange. Examples of varying factors within these standards themselves include the flange faces, the flange type and the flange pressure rating. Although produced to a given set of these ‘standard’ dimensions, flange faces generally are defined as any of the following: ring joint, tongue and groove, raised face and flat face. In addition there are many other less common variations. A flange can be offered to a variety of sub design types. These can include blind, weld neck, slip on, socket weld and lap joint. Flanges are also defined by pressure class. These allow a given flange to be able to withstand different pressures they are to be exposed to in service. As previously, flanges of differing standards are normally not interchangeable. Continuing with the ANSI/ASME working example, pressure rating options (defined in psi) can be 150, 300, 900, 1,500 and 2,500lb (125 and 250lb for flat face flanges only). As noted previously, there are a range of internationally recognised flange standards. Common examples of these are ASME B16.5 (½" to 24" Ø) and ASME B16.47 (26" to 60" Ø, Series A or B). This dimensional reference relates to the NPS or Nominal Pipe Size (aka Nominal Bore, sometimes referred to as NB in written descriptions). Both types are typically produced from a shaped or disc forging, then finished with machined and drilled surfaces. Additional information defines product into pressure classes (in psi): 150, 300, 400, 600, 900, 1,500 and 2,500lb (for B16.5), and 75, 150, 300, 400, 600 and 900lb (for B16.47). It is important to note these pressure classes are not linked directly to a flange’s maximum working pressure. This is determined additionally by the base material it consists of, as required by its final working application and decided by the pipe engineering teams at the start of a given project.

Pipe flanges The most common method of joining together two pieces of pipe is through a flanged connection. Each of these connections (generally speaking) is comprised of a gasket, some fasteners (the volume/size of which is defined by the flange size and type) and, finally, two flanges. For the purposes of this example we are assuming metallic materials. The gasket acts as a sealant. It is sandwiched between the faces of two mating flanges. This can be in pre-machined grooves on flange faces or the entire flat face of the flange. The fasteners act as the compressive force once tightened after being inserted through the outer bolt holes. Fastener tightening, application-dependent, is done in a specific order so as to maintain seal integrity. Connecting pipe in this manner means the joint itself is not a permanent one; however, it often remains in situ for great lengths of time. Globally, there are many differing flange standards. Readily recognised ones include, but are not limited to: AFNOR (French), DIN (German), JIS (Japanese), KS (Korean), ANSI/ ASME (American) and BS (British). Each of these have Flanges are used in a wide variety of applications, across a wide variety of sectors, in a wide variety of working environments. This article highlights two specific examples of flanges manufactured in-house by Alexander Comley within the plethora of flanges available today – ‘standard’ bolted pipe flanges (specifically ASME standard), and ‘special’ flanges (in the form of critical, internal, 2,220+ multi-holed product for process equipment). A flange as defined by Collins dictionary is “a projecting disc-shaped collar or rim on an object for locating or strengthening it or for attaching it to another object”. This benign description does not reflect the true importance this product undertakes within its daily working function. In an attempt to gain perspective in terms of an O&G or power and process project, piping and its associated component makeup (which includes flanges) is one of the key considerations in terms of construction staff, engineering and monetary value.

Flange materials can be commonly defined within the ASTM standards. Examples for piping applications in ambient/high

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Tube ProducTs InTernaTIonal May 2016

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