Socket Weld Flange

ASME B16.5 Class 150 flange dimensions

Flange outside diameter, minimum flange thickness, bolt circle, bolting and raised face, in millimetres, for NPS 1/2 to 12 in. These dimensions are set by the size and the pressure class and are common to the flange types on this line; the bore, hub, socket or thread detail changes with the type and is confirmed on the drawing or the quotation. Thickness includes the 1.6 mm raised face.

Data to ASME B16.5; confirm against the project specification before fabrication. Sizes above 12 in and Class 300 to 2500 follow the same layout and are quoted against the specification. Send the size, class, facing and destination port and we will confirm availability and price within one business day.

What a Socket Weld Flange Is

A socket weld flange has a recessed socket in its bore. The pipe end is inserted into the socket and a single fillet weld is run around the outside, so the pipe does not have to be bevelled and no backing ring is needed. Because the pipe sits inside the socket, the two parts are held square to each other while the weld is made, which is exactly what small bore work needs – a small bore butt weld is difficult to fit and to examine.

Size Range and Where It Fits

Socket weld flanges are a small bore product. ASME B16.5 tabulates them up to NPS 4 in the lower classes, and the highest classes stop at NPS 2 1/2, so a socket weld flange cannot be ordered in the larger sizes at all. Typical uses are instrument and impulse lines, small bore drains and vents, chemical injection and sampling points, steam tracing, and small bore connections on high pressure equipment where a welded joint is preferred to a threaded one.

Installation Points That Decide Whether It Leaks

The pipe is pushed into the socket but not hard against the bottom: a gap of about 1.6 mm is left before welding, so that the pipe can expand with the heat of welding without cracking the weld or the flange. Skipping that gap is the most common cause of a cracked socket weld. The single weld is a fillet, so it is examined by dye penetrant or magnetic particle testing rather than radiography. The pipe end must be cut square and deburred, and the socket must be dry and clean before fitting.

Limitations to Know

Because the weld is a fillet, a socket weld joint cannot be radiographed, and it should not be used in severe cyclic service. Fluid can collect in the gap between the pipe end and the bottom of the socket, so socket welds are avoided in highly corrosive or sour service where crevice corrosion is a risk. And because the recess is in the bore, a socket weld connection is not the choice for large sizes – above about NPS 4, butt welded connections take over.

Welding sequence and gap control on a socket weld

A socket weld joint is made in five steps, and the gap sets the other four.

What the documents and records should show

• On the flange: the class, size, grade and heat number in the marking, with a mill certificate to EN 10204 3.1, and 3.2 or third party inspection where the project requires it.
• On the weld: the welding procedure reference, the welder identification, the gap actually set, and the result of the dye penetrant or magnetic particle examination.
• On the flange drawing: the inside and outside diameters of the socket matter as much as the face — a socket that is too deep hides the pipe end, and one that is too shallow leaves the weld with nothing to fuse to.

Source: socket weld dimensions and pressure classes from ASME B16.5; the gap, examination method and record requirements are those of the piping code applied to the installation, and should be confirmed against the project specification.

Grades supplied and minimum properties

The grade fixes the minimum strength and the chemistry. The table below gives the requirements that separate the forged flange material grades ordered most often; the full composition and mechanical table for each grade is on its own page.

The complete chemistry and mechanical table for each grade, with the notes that qualify it, is on the individual grade page – for example ASTM A105 flange. The stainless grade has the higher tensile requirement but the lower minimum yield strength, so the two are not interchangeable on the strength table alone. The pressure class sets the flange dimensions, so the grade does not set the wall.

Source: specified minimum yield and tensile strength for each grade, per ASTM A105 / ASME SA105 and ASTM A182 / ASME SA182. The standard named against each grade is the governing document.

• A105
• A350 LF2
• F11
• F22
• F304
• F304L
• F316
• F316L

Download Socket Weld Flange data sheet (PDF) One page: supply range, grades and key sizes, what to state on the enquiry, and the inspection documents that come with the order. The standard is the governing document.

What decides the price

There is no list price for flanges: the same drawing can be quoted at different numbers depending on seven things. Send them and the quotation comes back within one business day.

Reply within one business day. Send the seven items above with the quantity and the destination port. Send the specification or WhatsApp the specification.