What to pay attention to when choosing flanges
Flange fasteners are necessary to connect the pipeline elements. Their choice should be approached with full responsibility, especially when laying pipeline systems for the transmission of dangerous compounds, the output of which to the surface as a result of an accident entails large losses and causes serious harm to the environment. This is most relevant when installing oil pipelines.
Standards of the main types of flanges
The following types of flanges are most popular in the CIS countries:
- steel welded flat;
- steel butt-welded;
- loose steel on welded rings.
The GOST number for the first type is 12820-80, for the second — 12821-80, and for the third — 12822-80. Regulatory documents contain installation conditions that differ due to design differences.
Distinctive features of flanges
The flanges also differ in the following parameters:
- type of section;
- conditional passage;
- rows;
- sustained pressure.
The cross section can be round and square. Oval shape is less common. Round sections are the most common, since most pipelines have exactly a round section. When choosing flanges, this should be taken into account: square products, due to their low prevalence, are produced in limited batches, often you have to make a special order. It is also necessary to take into account the installation of which fittings is possible, for example, a ZKS wedge gate valve or other elements.
The conditional passage is the area of the flange through which the working medium of the pipeline flows. The most popular diameters of the conditional passage are 100, 125 and 150 mm. All diameters have a letter designation determined by the tables. There are flange diameters above 200 mm, they allow a gap, but not more than 5 mm in outer diameter.
The flanges are divided into two rows, they differ in the number and diameter of holes for fasteners and bolts. By default, flanges for row No. 2 are used, unless this is specified in the order.
One of the most important selection criteria is the sustained pressure. It depends on the method of manufacturing the sealing surface and the geometric dimensions. Steel free flanges on the welded ring and steel flat welded flanges can withstand up to 25 kgf / cm2, and steel butt—welded - up to 200kgs / cm2.
When choosing, you should carefully monitor the pressure measurement units to avoid inconsistency of the required quality.