Choosing a Welding Coupon

[MrGezus]

Good afternoon, eng-tips! I will outline my question, code requirements, and thoughts.

My question is about tempering temperature on 4130 and will be below. I have gone through our inventory of material to try and choose the best coupon suited for an updated SAW welding procedure with a prolonged PWHT. I currently have one with only a 4 hour cook that was done long ago. We now have a need to match this process to others with an 8+ hour (1150-1200°F) PWHT. So far I have found a few pieces of material that I am considering. My criteria on looking through our inventory was the following:

Carbon Content - I am trying to get the lowest that we have for hardness/preheat purposes. Everything is between .309-.32

Vanadium Content - Same thing here. The lower the better. Range of inventory: 0.006-0.035. I have heard/read that this is will increase hardness

Tensile/Yield - Considering the prolonged PWHT on the coupon, I am trying to find something well above the minimum of 75ksi yield. I am making an assumption and going off of past data that it can drop >5ksi if the interpass temperature is too great along with the PWHT.

Hardness HB - So far my choices have come down to a few coupons in the range of 217-225.

Charpy: 15/20 ft/lb

CODES: API 6A / ASME IX / NACE MR0175 / DNV OS-E-101

The big question I have is how much affect will the tempering temperature of the base metal effect the HAZ (250 HV max.) after welding and PWHT. I know that the tempering temp (from the mill) effects the hardness of the material, but not sure if it has much bearing on the welding side of it. I would imagine it does. Our PWHT maximum temperature will be 1200°F (I usually cook at 1175°F). Out of the coupons that I am considering, the tempering ranges are 1202 - 1300°F. In the past it was told to me that a good rule of thumb is 50°F below the temper So i always chose a coupon with ~1200°F temper. Would it be that detrimental to use a 1300°F temper being that I can only hold a 1200°F max PWHT?

See attached for what I am looking at. Thank you everyone who read through this!

 

[Don56]

Check your spreadsheet. Your tensile & yield values are reversed. You are proposing to weld a coupon for a PQR. You want this to be useful for future welding. Your PWHT temp should never be above the tempering temperature. If the minimum tempering temperature can be 1200 you should keep your PWHT temp to 1150 maximum by your own logic. I wouldn't qualify a PQR with a PWHT at 1200 just because that specific coupon was tempered at 1300. What will you co in production when you have material tempered at 1200?

 

[MrGezus]

Check your spreadsheet. Your tensile & yield values are reversed. You are proposing to weld a coupon for a PQR. You want this to be useful for future welding. Your PWHT temp should never be above the tempering temperature. If the minimum tempering temperature can be 1200 you should keep your PWHT temp to 1150 maximum by your own logic. I wouldn't qualify a PQR with a PWHT at 1200 just because that specific coupon was tempered at 1300. What will you co in production when you have material tempered at 1200?

Thanks for catching that. I was in a hurry putting it together yesterday. I agree that the PWHT should never be over tempering temp. Most of the material we get will be tempered around 1200. I was just curious if it would be detrimental to use a 1300 tempered coupon during PQR testing. It has a bit lower hardness and strong mechanicals. That's the only reason I am considering it even slightly.

I do get your statement about if in production we have a part tempered at 1200 and our WPS states 1175-1200. I'm sure cooking that closely to temper wouldn't be so great.