What should be the PWHT Temperature of AISI 4130 material 2

[bmoorthy]

Background information:
An AISI Forged (Quench and Tempered) Cylinder around 500mm dia and 250 mm thick has been machined to hollow and complex shape.

Subsequently this gets welded to another AISI 4130 Component (Which again is QT and machined from another cheese block shape).

Subsequently the item is deposited with Inconel 625 from inside. inconel 625 is 5mm thick.

The Thickness at weld joint is 65mm.

The joint will be radiographed. (Including Overlay)

Governed by API 6A.

What should be the PWHT temperature?
Are ther any temperature zones that needs to be avoided (From the point of view of AISI 4130). We are not too worried about 625 welds as we are confident of passing the required corrosion test G 28 practice A and G 48 Practice A.

 

[metengr]

bmoorthy;
Considering your application, I would use ASME B31.3 as a guide for PWHT time, temperature, and ramp rates for this material. Per Table 333.1.1 for P-No 4 steels, you are looking at 1300-1375 deg F for 1 hour per inch of nominal thickness.

 

[jackboot]

bmoorthy,

I have several qualified weld procedures for 4130. However, I am assuming you are trying to qualify welding procedure - please do not weld any API 6A equipment without a proper welding procedure.

4130 and 4140 are nightmares to weld in the ASME/API coded world. You are specifing 4130 Q&T - however, you will probably notice that you can get a wide range of properties with very similiar heat treatments. Your welding procedure Post Weld Stress Relief (PWSR) will be highly dependent on the temper temperature of your 4130.

Rule of thumb #1 - go 50 degress below your temper temperature. Naturally, if you go higher than the temper temperature - you have ruined your material and your MTR is now invalid.

Rule of thumb #2 - make sure your material used in qualification is very typical of what you receive for your welding jobs. Once you have qualified your welding procedure you will only be able to weld a very narrow range of 4130. Why? Because your welding procedure will only be valid for +/- 25 degrees (F) of your qualification PWSR.

So, if you qualify your procedure on some material that has a temper temp. of 1300 - you will PWSR at 1250 F (1 hour per inch is good). However, your production parts may come in at say - 1265 temper temp. Now, your procedure is only good to 1225 to 1275 (+/-25 of 1250). You are still safe as long as you have a good controller on the oven temperature.

Please note that API 6A is not very friendly to welding on "non-recognized" materials such as 4130 and 4140.

My suggestion is to find you a good metallurgical lab to help pass the procedures and offer suggestions.

You will need two procedures - one for the overlay and one for the 4130 to 4130. For your 625 overlay - go with a GMAW ERNiCrMo-3 with 100% Ar gas. This will give you extremely low dilution which API weld procedure will require. 300 F/hr ramp time; air cool below 800 for PWSR (temper will vary as explained above). You may be able to go lower than the 50 F below the temper temp if you have time to experiment with your procedure (this would afford more flexibility in your procedure if you can get away with a lower PWSR temperature).

I don't know what mechanicals you are working with so I can't comment on the 4130 to 4130 joint. If you are using Enconel - I assume H2S (NACE) material - so you will be at 75,000 to 80,000 psi yield. The PWSR will be the same regardless. Remember your preheat will need to be about 400F to 500F.

Hope this helps.

jackboot

 

[metengr]

Rule of thumb #1 - go 50 degress below your temper temperature. Naturally, if you go higher than the temper temperature - you have ruined your material and your MTR is now invalid.

Truism to #1 - for materials used in pressure retaining items, the tempering temperature is usually specified as a minimum not a maximum. So, your tempering below 50 deg F is not an entirely correct assumption. For pressure retaining applications where quench and tempered material is allowed by Construction Codes, the PWHT temperature range must be high enough to reduce residual stresses and reduce the hardness of the base metal weld heat affected zone. Typically, the PWHT temperature ranges in ASME B&PV Code and ASME Power Piping Codes are at or below fabrication tempering requirements.

Rule of thumb #2 - make sure your material used in qualification is very typical of what you receive for your welding jobs. Once you have qualified your welding procedure you will only be able to weld a very narrow range of 4130. Why? Because your welding procedure will only be valid for +/- 25 degrees (F) of your qualification PWSR.

Truism #2 - in accordance with ASME B&PV Code, the PWHT temperature that is qualified for a WPS can be any specified temperature range (i.e., 1200-1300 or 1100-1200, etc) where the maximum PWHT temperature is below the lower critical transformation temperature.

 

[bmoorthy]

jackboot (Mechanical)

Thank You fo your Rule of thumb Number 1

What about rule Number 2?

Is there some specific clause in 6A regarding this +- 25F Degree Window ?

I concur with Metengr's point of view (Since it is true for ASME jobs), is there some thing specific in API 6A?

Thank You Metengr for Truism 2:
But does ASME Sec VIII or Sec IX give such valid range for WPS.
Specific Question : If a PQRT was conducted on a specimen that was heat treated at 1200 Deg F, then is it permitted to use the PQR to support a WPS to weld a joint that will be heat treated at 1100F or at 1300 deg F?

 

[metengr]

The Code recognizes when you qualify a WPS for PWHT, you normally select temperature limits on the WPS that fall between the minimum PWHT temperature specified by Code (these are the PWHT requirement Tables) with a reasonable temperature spread that assures you will not exceed the lower critical transformation temperature in production. Most of the temperature limits I see on procedures contain a 100 deg F spread in temperature starting with the minimum specified to assure remaining below the lower critical transformation temperature. The philosophy of the Code regarding use of materials is that when you exceed the minimum PWHT temperature for materials used in the production of boilers and pressure vessels you have assured adequate ductility and substantial reduction of residual stresses of the material to avoid problems in service.

When you qualify the WPS with PWHT, as long as you perform a PWHT on the PQRT that is within the PWHT temperature range specified on the WPS, you are good to go. However, if you were to have a temperature excursion that either exceeded the upper temperature limit on the WPS or resulted in you reaching the lower critical transformation temperature, the WPS is not valid.

Outside of boiler and pressure vessel repairs or other Code of Construction requirements, you are kind of on your own when it comes to welding. For welding of steel or low alloy steel that requires a specified range of mechanical properties by design, you need to carefully select your PWHT time and temperature range to avoid adversely effecting base metal properties (as stated in rule of thumb #1). Your range of PWHT temperature limits can be set by you and can be as tight or as loose as you want them.