[MW:15142] Problem about Positive material Identification(PMI)

Dear all,

 

In our  boiler one major problem occurred in Positive Material Identification(PMI) test [Spectrum test].  

 

Description	Reheater finishing outlet(RHFO) coil
Material	T91
Size	ø 63 x 4
Process	GTAW only
Filler wire	ER 90S B9
Filler wire Manufacturer	D & H Secheron
Preheating °C	185
Rate of Heating  °C	100/hr
Interpass temp  °C	190
Post heating  °C	100
PWHT  °C	750
Soaking Time	90 minutes

 

Around 800 joints welded in the above approved procedure only. Filler wire, header stub, RHFO coil, weld metal undergone PMI test separately and all show positive material results as T91 except weld metal. Weld metal shows the Chromium content only  as (4-7%){Reqd is 8-10.5%}.  We can't find how it happened? Our Chinese consultant told to cut and reweld all the joints. But our contractor argued that we followed approved procedure and used approved vendor's consumable only. Please give a solution. Here I have attached one preheating cum PWHT chart of RHFO joints(for 11 joints,5 thermocouples,1 recorder).All 800 joints are not checked yet. Only 40 joints checked and all 40 weld metals shown low Cr Content.

Please go through the below readings of one RHFO joint.

Description	Filler wire	Header stub	Weld metal	RHFO coil
Alloy	T91	T91	A-2	T91
Cr	8.94	8.34	5.19	8.68
Mo	0.96	0.90	0.93	0.92
V	0.17	0.17	0.08	0.19
Ti	0.07	0.10	0.04	0.03
Mn	0.60	0.40	0.54	0.63
Fe	87.81	88.11	90.86	87.61
Ni	0.12	0.33	0.20	0.38
Cu	0.02	0.16	0.20	0.16
Nb	0.09	0.08	0.03	0.04
W	0.15		0.00

 

Waiting for your valuable suggestions.

Thanks & Regards

K Mohamed Jubair

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