Weld Roof Panel Tube to Boiler Drum 2

[pootong]

Roof panel tube is designed to connect with steam drum by using tube expander without seal weld. Our erection contractor installed two roof tubes (dia 1 1/4") to the drum by using seal weld wihtout our permit. Is there any damage to the drum metal structure? No heat treatment was provided before and after welding operation. Drum thickness is 110 mm carbon steel ASTM A516 Gr.70 How to determine the damanges and how to rectify it?

 

[metengr]

Technically, this is a serious nonconformance. Is there any damage to the drum metal from the seal weld? Only from the local heat involved by seal welding.

Does the erector possess some type of National Board R- Certificate of Authorization or have any other reputable certification to perform qualified welding on boiler pressure parts?

If not, I would remove the seal weld, extract the panel tube, and perform a wet fluorescent MT of the drum surface where the seal weld was deposited and tube hole to assure no defects. If this is acceptable, I would re-install a new panel tube using the correct method.

 

[davefitz]

As I recall, there is usually a prohibition against welding on the 516 gr 70 material after it has been fabricated and stress releived/heat treated, because striking an arc during welding will cause microcracks to form near the strike. This brittle material may be susceptible to crack propagation, espescially during hydrotest at low water temperatures. The notch toughness, or protesction against this crack propagation, can be improved by add'l heat treating, but the shop records might need to be reviewed to confirm the add'l heat treating was performed.

 

[metengr]

davefitz;
SA 516 Grade 70 is very weldable provided proper preheat maintenance and required PWHT practices are performed in accordance with applicable codes and standards. I would question if the steam drum is really SA 516 versus SA 515 Grade 70. SA 516 Grade 70 is designed for lower to moderate temperature service so it would have enhanced fracture toughness.

The issue with post fabrication welding on SA 516 pressure vessel plate concerns loss of toughness from extended PWHT cycles. The SA 516 grades today can be specified with lower carbon equivalents and quench and temper heat treatments to assure thru thickness mechanical properties and fracture toughness after welding.

In this case, there is not much one can do other than perform NDT and assure no cracks were formed from hydrogen caused by seal welding with no preheat. Additional grinding can be performed to remove the locally hardened heat affected zone (which would extend about an additional 1/8" into the drum metal surface) along the drum ID surface.

 

[pootong]

Thank you all, I would give you more explanation as follows, seal weld was performed without any visual damage. It has a good appearance and material for steam drum is ASTM A 516 Gr70 for sure. Our erection sub contractor has no National Board R- Certificate of Authorization. It's very difficult to find certified boiler erection contractor in our country but they had experince in many boiler erection. I will suggest to do MT for crack examination, if any crack is found, can we repair and how?

 

[metengr]

Yes, a local weld repair can be performed on this material in accordance with the National Board Inspection Code (NBIC) using elevated preheat and low hydrogen weld rod. Please inform us of your MT results, and I can provide you those details.