PIPE JOINTS

PIPE JOINTS

Pipe Joints are used to couple runs of piping, to provide branches from Main Header , change the direction , connection to Valves & Equipment .The common types of joints are :

Butt welds
Socket welds
Threaded Joints
Bolted Flanges
Mechanical couplings.

1) Butt welds:

Butt welded joints are most common types of joints used for 2 inch and higher dia Piping.This type of joint is not normally used on below 2 inch & below, except when High stress , corrosion or other conditions that would affect joint. The end preparations are designated by welding codes and standards.

2) Socket welds:

Socket welds joints are almost used in joining small bore piping. The joint is fit up by slipping the plain end into the Socket connection.A gap of 1/16 inch at the bottom of the socket is normally required to allow expansion between the fitting and pipe.This prevents the weld from possibly Cracking due to thermal Stress during welding or High temperature services.

3) Threaded Joints:

Threaded joints are normally used on low pressure system. Pipes & Fittings for threaded joints in low pressure system usually have National Pipe Taper (NPT) threads.A pipe joints compound or thread sealant must be used to prevent leakage around threads joints.

4) Flanged joints:

Bolted Flanged Joints are required where Pipe , Piping Components , or Equipment must be disassembled for maintenance. The are required when Joining Glass , High Density polypropylene , or other lined piping.Sometimes they are used to join Prefabricated shop spools.

Flange Bolting Procedure:

Flanges have equally spaced Bolts in multiple of four , so that valve or fittings can be positioned to face in any quadrant . Identification symbols are used for flange Bolting.All bolting must be long enough to ensure that the bolt will have one or two threads showing beyond the nut when joint is complete.

Both excessive or inadequate initial bolt stress can cause leakage at the joint. Accurate prestressing of the connection is required for proper operation. Prestressing Methods include :

- Tightening by Hand Wrench

- Tightening by Calibrated power torque wrench

- Hydraulic tensioning

Before prestressing , all bolts should be thoroughly coated with an antiseize compound to allow removal .Bolting sequence is not performed in clockwise rotation , but across the face to properly draw the flanges together .Also stress on bolting should be increased in a step manner to bring the bolt up equally to prevent from rolling the gasket. Both of these two actions helps in stopping poor gasket setting , which can cause leakage.

To assemble Bolted Flange Connection :

- Thoroughly clean the flange faces prior to fitup

- Rig the flanges into position with the bolt holes aligned & check flange Faces for parallelism using a dial indicator or other means.

- Provide coating on Flange bolts & install gasket , bolts ,nuts.

- Tighten Flange bolts in sequence as shown in figure