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Dear All,
Please help me to clarify the issue with welding parameter calculation. Recently we have carried out some PQRs, Client disagreed with us on calculation of parameter in WPS.
For Example, the amperage recorded in PQR was 200 – 250A.
When we applied the tolerance for amperage (increase or decrease 10%), the values obtained in WPS should be 180 – 275A.
Client’s idea was that the tolerance shall be imposed on the average value of these amperage, was 225A. So, the values in WPS should be 202.5 – 247.5A.
According to our calculation method, the range shall be wider. So, please give me some advices, or convincing cites on this issue.
Thank you very much,
Hi razormeback,
Welcome to the AWS Forum!
Your PQR should not have a range. It should have the average value (225 A). The PQR is a document that records the actual parameters that you performed the test.
The WPS should specify the range (180 - 275 A). The WPS is the document that shows the allowable range (tolerance) that the parameters can vary. Set your range to what you believe your process is capable of producing a sound weld.
Tyrone
Interesting comments Tyrone.
As you state in one sentence, the PQR should record actual parameters used. I agree.
In another sentence you said the PQR should list an average value of the parameters used to weld the test assembly. Which is it, the actual values or the average values?
How are you determining the average values for each parameter? Simply taking the high and low, adding them and then dividing by 2? Or are you recording the parameters used for each weld bead and then averaging?
The latter would be a more accurate method.
I record the parameters for each weld bead and use Excel's statistic package to find the average, median, and standard deviation of the voltage, current, wire feed speed if applicable, and travel speed.
Best regards - Al
Al,
What I meant to say was that the PQR should have an actual single recorded value. Just thinking more about stats, the median would probably be the most accurate number since the weld process is most stable at the reoccuring numbers.
Tyrone
In fact, there is alway a range of welding parameter for PQR due to the amperage or voltage is not perfectly stable even Manual, Semi-auto or Auto Welding, however the variation of welding parameters are not much, e.g. 2 to 4 amps. We just record the actual value of welding parameter while running the PQR.
For welding parameter calculation while developing WPS you should base on Heat Input which combines Amperage, Voltage and Travel Speed. The Heat Input shall not deviated more than 10% of recorded PQR.
When determining the appropriate ranges, it goes back to the governing welding standard. In the case of ASME Section IX, "good engineering judgment" is the basis of the determining the ranges since one does not have to record the actual parameters on the PQR.
When working to AWS D1.X, I qualify the fillet welds first to determine the appropriate ranges that provided the required weld size and proper fusion to the root. Then, using those parameters, I qualify the V-groove to verify the mechanical properties. The ranges on the WPS are listed using the +/- permitted by the welding standard for the largest single pass fillet, smallest multipass fillet, and the grooves using the median of the ranges for each weld type recorded on the PQR.
Best regards - Al
Dear 803056 and All,
Seems the method of calculation of parameters shall depends each engineer's experience while AWS or ASME code does not give clear guidelines for this problems?
Best Regards,
I'm going to respond a little rougher. Your clients are idiots. .5 amps??? Come on!!
The plus or minus 10% you utilized is not only reasonable, IMO it is a bit restrictive. The range you used will not expand the normal scatter band for tensile properties and will not be the difference between success or failure of bends (except for some alloys). By the time you factor in variances of welder skill, filler metal characteristics, machine characteristics, etc., you think in terms of broadening the range. This is the engineering latitude intended by ASME.
You may wish to be more restrictive when it comes to other testing regimes such as CVN's but that is not the current context.
So, the question for Razormeback is this: What is the metal you're welding and with what type of filler metal if specifically required?
Respectfully,
Henry
Dear Ssbn727,
I'm using ABS EH36 (AWS Group II) as the base metal and filler metal is flux core wire E71T-9CJ (CVN Test at -40.deg C). We are going to carry out many PQRs in the near future using variety of materials and classes of filler metal.
My concern now is just about the method of calculating parameter for WPS from what recorded in PQR. Does codes give any mandatory details for applying the tolerance of parameters (Para Process Parameters -Table 4.5) on just average value, because we have made many WPS applying the tolerance on a range of value for years and found no problems from other Clients.
Thank you all for taking interest in my issue.
How about welders using a remote device when welding to alter current or changing travel speed depending on where he is welding on the pipe? How is this controlled and documented on the WPS? Difficult.
In my opinion if you are welding low temp steel the easiest way to control heat input is to record bead/weave widths for each pass during the welding procedure qualification test. Amps/travel speed/heat input calculation may not mean much to a welder but if your WPS says no wider than 12mm then he has a clear understanding what is required. Opinions please.
Nantong,
I've used that methodology for controlling excessive heat input in Production. It works, but it took some time for the Welders to ajust to the limit.
Tyrone
Generally, when working to AWS D1.X structural welding codes, I qualify the fillets to establish the welding parameters needed to produce a sound weld of the required size for both large single pass fillets and small multipass fillets. I then determine the mechanical properties by welding a grooved test assembly that incorporates the high and low parameters used to qualify fillet welds. If the electrode diameter is held constant for both the fillet welds and the grooved plate (or pipe), only the travel speed has a "wide" range. The other parameters may vary, but the ranges are relatively tight.
The ranges for the WPS are relatively "wide" as permitted if it is supported by multiple PQRS (both the fillet welds and the grooved test assemblies). That approach does not tie the fabricator's hands with overly restrictive ranges for the parameters. The WPS is then supported by "real" test results. It really isn't that difficult.
Al
I have a situation that the client frequently makes a tight parameters monitoring in my shop floor and I need to qualify a WPS with a wide parameters range, eg. 170-280A / 21-29V / 10-60cm/min and heat input max 30.000J/cm - FCAW - 6G - Material ASTM A572 Gr 50 Group II - CNV required 0°C - no hardness required.
Is it possible to write one WPS with those ranges described above using a single PQR in which the minimum and maximum parameters were performed? (Presuming the mechanical and soundness tests are approved)
Dime,
WELCOME TO THE AWS WELDING FORUM!!
Wish you would have started your own thread instead of opening an older existing thread to ask your question but not to worry. I'm sure some of the experts in PQR's will be along.
That's quite a range you want there. Probably too much in my book but need to look some things up to see how it fits together with all your information.
FCAW: what electrode class/spec and what diameter? What material thickness and I presume pre-heat is applied if needed.
He Is In Control, Have a Great Day, Brent
Once a PQR assembly has been welded, the parameters recorded, and assuming the notch toughness requirements are met, the range of the welding parameters is severely limited for the WPS.
One can weld two (or more assemblies) using low preheat, low voltage, low amperage, high travel speed to produce low heat input. Assuming the test requirements specified by the Engineer (assuming D1.1 is the governing standard) the ranges of the WPS are specified.
A second test assembly can be welded using high preheat, high voltage, high amperage, low travel speed (wide weave beads) and again, assuming the test assembly passes the requisite testing regiment, the ranges of welding parameters are established.
The two PQRs can then be used to write the WPS. The ranges of welding parameters can then include the full range of parameters established by both PQRs A and B.
Under the auspices of AWS D1.1, the Engineer must specify where the CVN specimens must be removed from the test assembly, the test temperature, and the required test results for CVN. The requirements for soundness and tensile strength are specified by the code.
Best regards - Al
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