We do T-Bar fillet welding in a work shop.  FCAW  process plate grade AH 36   web pate is 1/2”(12.7 mm) thick and face plate 5/8”(16 mm) thick. Ambient temperature 25-30 degree C. according to D1.1 code minimum  preheat is 0 degree C. So we not apply preheating before welding. but some of CWI tell us that we must  do preheat  to remove moisture before welding don’t care about ambient temperature because every steels surface have moisture. I have confuse about this moisture he have mention. it is correct? How to identify or measurement that steel surface have moisture? Thanks in advance for u advise.

  S. WINAI

Hello fellow welding gurus:

I am not sure what you really want to know. I am not sure there is really a question being asked. Here goes nothing.

Preheat (AWS A3.0-2001
preheat. The heat applied to the base metal or substrate to attain and maintain preheat temperature.
preheat temperature, welding. The temperature of the base metal in the volume surrounding the point of welding immediately before welding is started. In a multipass weld, it is also the temperature immediately before the second and subsequent passes are started.

The preheat temperature is the ambient temperature if no supplemental heat is added. However, ambient is not a discrete value and it is not the temperature recorded on the procedure qualification record (PQR) when the welding procedure specification is qualified by testing. The value recorded on the PQR is the actual temperature of the part just before the welder strikes the first arc.

If supplemental heat is used, preheat is still the temperature of the parts just before welding is initiated. The source of heating is not important. If could be the result of preparing the weld joint by grinding (friction), heating the part in an oven or by heating it with a torch or electric resistance heaters. Preheat is still the temperature of the part just before welding commences.

In the case of welding steels, preheating is often used to reduce the cooling rate to mitigate the formation of undesirable phases, i.e., microstructures, which tend to be sensitive to delayed hydrogen cracking or have a propensity to harden.

Welding standards typically include ranges for welding parameters used in production that are based on the parameters used when the test coupon was welded. The lowest preheat temperature is usually limited by the applicable welding standard and is a function of the preheat temperature used when qualifying the WPS.

In the event the individual that witnesses the welding of the test coupon fails to record an actual temperature (a numerical value) of the preheat on the PQR, there is no basis of limiting the lower limit of preheat used for production welds.

Moisture
Many welding standards state that the surfaces must be dry and free of moisture before welding. The concern is free moisture on the surfaces or between components such as lapped members as a result of standing water, snow, ice, etc. The concern is twofold; the moisture can flash off as steam which can result in porosity or it can disassociate into hydrogen and oxygen. The oxygen can combine with carbon to form porosity and the iron to form oxides. The problems associate with oxygen can be mitigated by introducing deoxidizers into the weld pool. Atomic hydrogen, from the disassociation process, easily goes into solution with the molten weld pool. Much of the hydrogen escapes harmlessly as the weld pool solidifies. However some of the hydrogen can potentially cause delay hydrogen cracking under the proper conditions.

Supplemental heat can be used to hasten the evaporation of any snow, ice, or standing water.

As for how preheat is to be addressed in the WPS: Preheat temperatures listed on the WPS is the minimum preheat temperature based on the requirements of the applicable welding standard. The preheat temperature may be determine prescriptively as in the case of a prequalified WPS where the minimum preheat is determined by the thickness and chemistry of the base metal. As an alternative, the preheat temperature may be based on actual preheat temperature of the test coupon when it was welded.

The issue of wet surfaces can require the inspector or contractor making decision based on good engineering judgment. If the dew point is about the same as the ambient conditions, supplemental heat may be required to ensure there is no moisture between lapped members.Other considerations include the chemistry of the base metal and its poropensity to hardening and sensitivity to delayed hydrogen cracking. Increased carbon equivalency and high dew points can easily justify the need to use supplemental heating to ensure the base metal temperature is high enough to ensure the surfaces are free of all moisture even when not stipulated by the fabrication code.

There were many occasions where I used the torch to heat the base metal to evaporate surface moisture entrapped between lapped members. There was no need to “preheat” the steel, it was already above the minimum preheat temperature required by the applicable code. However, failure to completely dry the joint before welding would cause gross porosity. Closely related to this problem was the use of preheating cold steel in the winter. The preheat had to be maintained for a period of time to ensure the condensate from the torch flame had sufficient time to completely evaporate. Failure to evaporate all the moisture would result in porosity.

Moisture from the steel, i.e., subsurface moisture in the steel? I think not. The water molecule is too large to diffuse into or out of the atomic lattice and it cannot survive the high temperatures of the casting, rolling, or extrusion processes associated with making the primary shapes.

Best regards – Al

First one must identify who is responsible for what and what is the limit of their authority to make demands on the fabricator.

If AWS D1.1 is the governing welding code, the authority of the Contractor’s Inspector and the Verification Inspector are pretty well defined.

The third party inspector, i.e., the Verification Inspector, has very limited authority. In most situations the Verification Inspector’s tasks, i.e., scope of work, are defined by the Engineer. Likewise the authority of the Verification Inspector is determined by the Engineer.

In most situations, the Verification Inspector can do little more than report observations and non conforming work the Engineer. Code imposed minimum requirements are the only requirements the Verification Inspector can enforce through the Engineer. Whether nonconforming work must be repaired or accepted “as is” is the purvey of the Engineer.

The Contractor’s Inspector is in the best position to take immediate steps to mitigate conditions that may result in nonconforming work. In the situation we have been discussing, i.e., moisture between lapped members, the Contractor’s Inspector can require the welder to increase the preheat temperature or increase the time at temperature to ensure the moisture is completely evaporated. The Verification Inspector has no authority to make similar demands of the fabricator if the minimum preheat requirements are being met.

The Verification Inspector has no authority to insist or even suggest the means or methods the fabricator uses to fabricate or to make repairs. The Verification Inspector should not be involved in devising the method used to repair a weld. The Verification Inspector becomes part of the problem when they get involved in determining the method of manufacture or repair.

Every job is different than the last one, there are exceptions to everything, but the quickest way for a Verification Inspector to find himself on the outside looking in and asking,  "What just happen?" is to base accept/reject decisions on personal opinion or to offer “helpful” suggestions to the fabricator. It can be very difficult to stand by watching the fabricator flounder, but the Verification Inspector must stay at arm’s length from the fabricator. As soon as the Verification Inspector makes a suggestion or when the Verification Inspector imposes a requirement based on opinion rather than based on code, he has placed the hangman’s noose around his own neck. It is like cameramen watching a lion pounce on an unsuspecting baby goat. It hurts, you feel sorry for the fabricator, I mean baby goat, but that is just the way the world works.

You ask an interesting questions Brent. In my humble opinion, the individual rejecting a weld or member should be the individual that cites the specific code provision that is the basis of the nonconformance identified. It is not the fabricator's responsibility to disprove the Verification Inspector's claim. If the inspector that is rejecting the work cannot cite a code provision as a basis of "call", the nonconformance has no basis.

Best regards - Al

Early in my career an Engineer representing the State of North Carolina gave me very specific direction that I have never forgotten. It made sense then and it still makes sense. Essentially the little speech he gave me before I started the job went something like this:

"You were hired to be our expert. You are our eyes and ears on the job. As long as the fabricator is building product for our projects you are responsible to us and only us. You are expected to verify the work they do is in conformance with the project specifications and the code (D1.5).  You report any and all nonconformance’s to me. I expect detailed reports and details of any substandard work. I expect your report to specify what code provision or project requirement is not met and the extent of the problem. You are quality assurance, not quality control. You are there to make sure their inspectors do the required visual examinations and any additional NDT specified. You confirm their inspection reports are accurate and they are fulfilling their obligations as per the code and project specifications."

He went on to say, "My task is to make a decision based on your report whether the nonconforming part has to be repaired or accepted "as is". We do not determine how the nonconforming part is to be repaired. That is the fabricator’s responsibility. If he does not know how to make the repair, he can hire his own expert. If he asks for your advice, decline politely. You are to offer no opinion, offer no suggestions, even if and when the fabricator asks. You work for us, not for them."

He pretty well summed up the responsibilities of a verification inspector.

Best regards – Al