3 Pipe Welding Copper Nickel Alloy Part 3 of 5

Описание: Section 3- Copper-Nickel Alloy- Pipe Welding

The Copper Development Association is pleased to present a series of video presentations covering welding of copper-nickel alloy. This video is the third in a series designed to provide welders with the principles of joining 90-10 and 70-30 engineering grades of copper-nickel. In this demonstration we will be using a pipe which has a 200 mm diameter. While this is a common industry pipe size, copper-nickel alloy tube sizes can vary from small diameter, thin-wall condenser tubes, to pipes as big as 610 mm in diameter, and even larger.

The basic guidelines for TIG welding are covered in the Copper-Nickel Alloy -- TIG Welding video, and are applicable to pipe welding. Some important points to remember are:
The need for high frequency or a lift start, and a down-slope or current decay to minimize start and crater defects
Prepare Tungsten electrodes the same as you would for stainless steel
Use as large a cup size as practical or a gas lens
It is important to have a uniform root face, or land as it is often called, around the pipe circumference for the welder to make a uniform root pass. This is best done by machining, and an ID counter bore may be needed to correct pipe that is out of round.
The root pass technique is an area of flexibility and best results are often obtained using the technique the welder is most familiar with, allowing for differences in fluidity.
Fixed position pipe welding requires significantly greater welding skill than the easier down-hand welding, but high quality welds are readily obtained in the fixed position.
Before tack welding the pipe sections to be joined, an internal inert gas purge arrangement needs to be installed. There are many different pipe purging arrangements and hardware used in industry. Any of them used on stainless steel piping are acceptable for welding copper-nickel alloys. The purging gas should be 100% argon. The argon purge should be continued until all oxygen (air) is essentially eliminated. A high purity purge is needed during root pass welding to obtain a smooth internal root contour, free of an oxidized surface. The purge is maintained until at least the completion of the next fill pass to prevent oxidation of the weld area.
After the weld is made, post weld clean to a bright finish and visually inspect the weld to assure that it meets desired quality, the proper weld contour, and is free of defects such as cracks, undercut and lack of fusion & penetration. Both the ID root weld, when accessible, and the weld face should be visually inspected.