In the previous article, we mentioned the factors that need to be considered when choosing a welding process, but in order to provide some additional guidance, we summarize in more detail below the actual steps that can be taken to create conditions for a successful welding operation. This is roughly divided into the following 4 steps.
Condition of the butt fusion equipment
The condition of the butt fusion machine itself matters. If the machine is defective, then there is a good chance the welds will be defective. A simple checklist can be used to assess a machine each time.
The machine has a basic chassis onto which the pipe clamps (one of which is fixed and one of which is designed to be a moving half) and hydraulic pistons are fixed. The chassis should not be bent (check with straight edge tools).
(2) Hydraulic rams
The moving half of the machine should be cycled without a pipe in the clamps to prove that minimal ram pressure is needed to slide the clamps through the full cycle (proves low friction, rams or chassis not bent).
(3) Hydraulic hoses and connections should be checked to ensure they are leak-tight, that they are connected in the right sequence so that the moving half of the machine moves to open or close correctly when directed from the control panel. Pressure gauges should be calibrated and working.
(4) All electrical cabling, connectors, and environmental seals for motors and sensors should be checked to ensure they are undamaged either physically or from water ingress. To adjust the heater plate will require a surface contact thermocouple with calibrated temperature display available on the worksite.
Selection of butt welding parameters
As we have said earlier though, there are basic points to keep in mind if you do venture into adapting welding parameters to suit a particular site situation.
(1) The temperature around the heater plate where it touches the pipe is important. If it is too low then insufficient heat will be taken up by the pipe, if it is too high then potential degradation of the pipe material might occur, so a range is specified – usually 225 to 240°C, with the setpoint typically 230°C.
(2) When the pipes are first pressed against the heater plate they start to melt and a small bead is formed (this is termed ‘bead up’). The bead step compensates for some out of true in the machining stage, provides some of the compensation for pipe material temperature, and so on.
(3) After the bead is formed, heat is allowed to soak into the pipe ends. Enough heat must soak in so that it deals with the ambient temperature of the pipe material (adjust for extremes of hot and cold) and maintains at least a minimum temperature when the heater plate is removed and pipes butted.
(4)As well as temperature, the pressure applied to the pipe ends also matters. Too little pressure may be insufficient to move melt to cause defusion bonding and achievement of full strength, too much may simply squeeze all the melt out of the joint causing voids and cold lap weld conditions.
(5) And finally, leave the pipe in the machine when the weld is completed to allow the strength to develop – typically by allowing the bulk temperature or maximum temperature within the pipe to drop below around 80-90°C so that the material is crystallized. That is about the long-term reliability of the pipe.
Control of site conditions likely to influence the quality
A few simple precautions on-site can deal with common problems in welding processes and mostly this is thinking about the site conditions. When ordering equipment for site works, as well as the butt fusion machine itself, a tent and some temporary pipe endcaps can help provide the controlled conditions needed for successful welding.
(1) In preparing the work area it is recommended that a groundsheet is laid down underneath the butt welding machine and a tent is used to enclose it. This stops biological matter being drawn from the ground into the machine and airborne matter (e.g. dust) from being blown into molten pipe welds.
(2) Before using machines they should be cleaned, particularly the heater plates. These can be washed (along with their covers). Similarly, there is a practice known as ‘dummy weld’ where a pipe is pressed against the heater plate to remove debris (but not made into a joint, instead trimmed when cooled).
(3) As well as a strong focus on cleanliness, tents also assist in preventing wind chill effects drawing heat away from the pipe ends. Using temporary stoppers in the ends of the pipes being welded (ends furthest from the weld) stops significant cooling effects for wind chill caused by chimney effects.
(4) It is worth thinking about ambient temperature and temperature of the pipes to be welded and in extremes of hot or cold conditions adapting the process. It is reasonable to increase or decrease the heat soak times for example, for temperature extremes.
Commissioning the process on-site
Commissioning a machine on-site is a prelude to being confident that when multiple welds are made, which may involve considerable time and effort, that you are achieving good welds each and every time. There are many things that you can do, which include:
(1)We have mentioned many steps already about setting up the worksite with tents, for example, checking the machine is clean and fit for purpose (mechanical and visual checks), and basic functions work like heater plate temperatures and movement of the machine chassis.
(2) When you start the key is to ensure that the machine you have, the operator, and your chosen parameters can produce a good weld. It is quite easy to test a weld, particularly if you have a test center pre-booked (can be on-site) to validate the process before making lots of welds (recommended practice).
(3)Start by cleaning the heater plate at the start of commissioning a machine and perform 1 or 2 dummy welds so that you are satisfied there is no contamination.
(4) Make welds using your chosen parameters, either picked from a standard that you have selected and/or any adaptation made for your site conditions.
(5) Cut the first weld out, take samples around the full circumference of the weld and destructively test to check the weld is fully ductile (see test standards later).
If you want to know more about the butt fusion machine
after reading the above, you can get a comprehensive solution by contacting us.
RIYANG is a butt welding machine
manufacturer with many years of experience. We put our customers' needs first in everything we do, aiming to provide customers with effective solutions. For this, we are equipped with a professional manufacturing team and strict quality inspection system, which can control the quality of products in all aspects. At the same time, we will continue to adjust and upgrade R&D technology and design solutions according to the diverse needs of Russian users. If you want to buy our hot melt butt machine, please contact us immediately!