Re: [MW:15149] Problem about Positive material Identification(PMI)

Mr. Md. Jubair,

The mistake could have happened due to deficiency in the chemistry of the filler metal used for your welding.

It also happened to us years back, wherein an imported 2.50 Cr -0.5 Mo filler wire was actually found to have less than 1.75 Cr. and more than 35 joints done, were cut and re-welded.

Then onwards we made it a point to evaluate the chemistry, mechanical (if required) properties of the consumables (both filler wires & coated electrodes) used for such sensitive joints  like alloy, stainless steel or special materials.

 

Instead  of depending blindly upon on the manufacture's Test Certificate , it is always better to cross check the chemistry & mechanical properties  independently before using them for welding..

 

Otherwise, It could have been due to choosing a wrong filler wire by the user on the shop floor though AWS classification is  printed / punched on it. But it seldom happens.

 

Hence, please be alert in future and re weld the joints if required.

 

Sridhar.

,

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From: mohamed jubair <kmd.jubair@gmail.com>
To: materials-welding@googlegroups.com
Sent: Tuesday, 28 August 2012 1:55 PM
Subject: [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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