Welding of magnetized pipe
Welding of magnetized pipe
(OP)
we were doing welding job for inconel (3mm SS Clad internal) spools welding 34". the welders were unable to debosit the weld metal correctly in the root. what might be the reason? Magnetization? and how to know?





RE: Welding of magnetized pipe
Magnetic fields are created due to the welding current. Be sure that the pipe is properly grounded. Be sure that the welding cables are not wrapped around the pipe.
I assume that the pipe base material is stainless steel internally clad with Inconel alloy. Please confirm. Also what is the stainless steel alloy and the Inconel alloy designations?
RE: Welding of magnetized pipe
Bad cleanliness/not grinding to absolutely clean base metal/not wiping clean the surface after grinding with alcohol or cleaner?
Wrong electrode? Wrong current setting ? What kind of welding were they attempting?
RE: Welding of magnetized pipe
Your best bet is to use a demag unit for the root pass. Once the root is in place, the residual magnetism should subside to a workable level.
Failing the availibility of a demag unit, you can tightly wrap the welding leads close to the bevel. Be sure to use an odd number of wraps, preferrably five or more. This should reduce the gauss enough so you can perform the task at hand.
One thing to note is that that persons with imbedded cardiac appliances should not be performing these operations as it could affect the operation of the appliance. It can also negatively affect credit cards and other magnetic media.
RE: Welding of magnetized pipe
RE: Welding of magnetized pipe
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Welding of magnetized pipe
Johnny Pellin
RE: Welding of magnetized pipe
Recently, I came across requirement of Residual Magenetism (RM) values depending upon the pipeline welding process in one of the project specification for line pipe material. It was stated that if GMAW or GTAW processes are to be used for Offshore Pipeline Installation (Field Welding), RM should be less than 15 Gauss. DNV-OS-F101 allows upto 20 Gauss (average) and 25 Gauss (individual). My understanding is that weld arc blowing can be avoided if RM is limited to 20 or 25 Gauss for Carbon Steel line pipe.
1. Is there any limitation in achieving lower value of RM, say 15 or idealistically, near to zero?
2. Also, during the process of coating pipes, pipes are usually pre-heated to around 250ºC using induction coils. This results in the induction of residual magnetism within the pipes. How much RM can be expected at that stage?
3. Can we expect higher values of RM (greater than safe limit of 20-30 Gauss) after pipe manufacturing (including MPI) and pipe coating stages?
Thanks
RE: Welding of magnetized pipe
inductive de-gaussing works if you really need to meet a given spec, but time consuming, there are other methods but these are not generally suited to field fab
RE: Welding of magnetized pipe
I'm not a Tig {GTAW} welder, but a world-class one told me that the secret to Tig-welding inconel is to never dip the filler-rod into the puddle; just keep it close and allow it to drip into the puddle while concentrating on breaking down the sidewalls.
Try to 'borrow' a welder that is comfortable making x-ray & ultrasound acceptable inconel welds. Have him/her show your best welders the 'tricks' needed to make acceptable welds.
RE: Welding of magnetized pipe
RE: Welding of magnetized pipe
RE: Welding of magnetized pipe
RE: Welding of magnetized pipe
I had an issue with a heavily magnetized separator vessel in a supercritical boiler installation that was approximately 80 gauss at the welding end preps. After initial degaussing (had to call in Gaussbusters, as we were unsuccessful using induction equipment, and I was out of ideas after a week on the scaffold), we were around approximately 25 gauss, and a GTAW arc was still flip-flopping across the root gap.
A second run had us down around 20 gauss, and it was steadier, but still not adequate to install a GTAW root pass.
Third run had us down around 12 gauss, and they were able to put in a root pass without issue (2.25 Cr. material).