Preheat and Preheat Maintenance

[marcolino21576]

Dear All,

I have one question. Our welder is carrying out a qualification of a new WPS, by welding a cast coupon in duplex 2205 with duplex 2209. The welding activities shall be distributed during 5 days.

To reduce to minimum the presence of humidity on the weld, the welder shall lightly pass the flame of a burner on the weld surface. This is going to happen each day, before starting welding activities.

Should this "drying" activity be considered formally as preheating and (= should the temperature of the weld joing be registered on the WR?)

Thank you for your help

MC

 

[Mr168]

He's eliminating the moisture by elevating the preheat temperature, so yes, you would record the temperature of your coupon after "drying" as your preheat temperature in your procedure qualification, assuming you begin welding immediately thereafter.

 

[marcolino21576]

Thank you Mr168

this is exactly what I supposed.

MC

 

[jbeckhou]

Would you have a max and min temperature?

Petrotrim Services

http://www.petrotrim.com

 

[Eddycurrentguy]

It doesn't really matter why the preheat is applied. If you note the minimum temperature on the PQR and list a reasonable value on the WPS you should be ok.

 

[Mr168]

Unless codes dictate otherwise. A number of codes to have restrictions regarding preheat, typically a reduction in X number of degrees can be considered a change in essential variable.

 

[marcolino21576]

Eddy,

sounds clear to me.
I will note the minimum temperature on the PQR; isn't it mandatory to list the same minimum temperature on the supported WPS?

Jbeckhou,

I don't have a min/max value. The aim of the operation is just to eliminate moisture on the weld just before starting the welding activities at the beginning of the day; therefore, I expect the preheat temperature to be around 30-35°C.
I do have limitation on interpass temperature (150°C max), but that's another matter...

MC

 

[gtaw]

You will have to preheat the base metal to a temperature above the dew point. Since you are using a torch, moisture will form on the surface of the base metal as the H20, a byproduct of combustion condenses on the cold surface of the base metal. The preheat will have to be sufficient to evaporate any moisture present from the condensation. As you can see from the response, any heat added before welding is considered to be preheating, since the temperature is raised to something above ambient.

Best regards - Al

 

[Duwe6]

Let's keep this simple: a PQR is a report of the making of the Coupon. The *actual* temperature is to be recorded, Makes no difference how that temperature is arrived at.

When I write a PQR, the 'Preheat' on it is the lowest starting temperature. Likewise, the 'Interpass' is the highest interpass temperature used.

 

[gtaw]

I concur with Duwe6 comments. You record the actual temperature of the test piece at the start of each weld bead. The initial temperature recorded is the preheat temperature even if it is ambient (ambient by the way is not an acceptable entry). In other words, whether you increase the temperature before welding by heating the test coupon with a torch, by grinding the surfaces to remove oxide, or start welding while the temperature is the same as the surrounding ambient temperature, the actual value of the temperature is recorded on the PQR.

The interpass temperature is the temperature of the test piece once welding has begun. Usually the interpass temperature is measured adjacent to the location where the next weld bead will be initiated, just before initiating the arc.

Best regards - Al

 

[marcolino21576]

Guys,

your help has been much appreciated!