Re: Re: [MW:28567] Fw: Fw: Back Purging for fillet welds

But it has been brought into subject that for MIC failures at capital projects, this is also an one of the rootcase, regardless of layup issues.

Its like they have confirmed that by their through thorough investigation, that the cause of the leakages were pin-holes in several welds. Materials Specialist concluded that Microbiologically Influenced Corrosion (MIC) exists  in 2 inch and in a 10 inch austenitic stainless steel pipe on the ...... project.

My question is that because of not purging fillet welds on SS, a PIN HOLE occured and thus MIC exists?

If this is the case then last 1000 years of fillet welds on Ferrous (P8) and all non ferrous to be scrutinized.

Regards,

Muneeb.M

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From: Kannayeram Gnanapandithan

Date: 2018-11-01 08:43

To: materials-welding

Subject: Re: [MW:28543] Fw: Fw: Back Purging for fillet welds

not require for fillet weld.

THANKS & BEST REGARDS,

KG.PANDITHAN, BE, IWE,  CSWIP 3.1,

ASNT-Level II in PT,MT,RT & UT.

International Welding Engineer. 

CONSULTANT-WELDING & QUALITY

Mobile no: +919940739349

On Thu, Nov 1, 2018 at 9:24 AM muneebslsa@gmail.com <muneebslsa@gmail.com> wrote:

Greetings Experts,

Please go through the trailing mail and advise, this is a debate between i and owner representative when i was in contractor for the requirement of back purging for fillet welds, in this case i just need your opinion.

I have deleted the replies from owner representative as i feel its confidential and you will find only my writings for the subject.

Please advise.

Regards,

Muneeb.

Subject: Re: RE: Back Purging for fillet welds

Greetings,

We requested this below butt weld joint for RT, which is stainless material including the wear pad, please find the RT film which is accepted with NSD by QCS RTFI.

Hence concluding that no oxidation / doubtful inclusions or doubtful debris found, regardless to back purging for fillet weld which is non requirements.

Also, some of the non releavent standards codes has been referred below for your just reference for the acceptable level of heat tints / oxidation / discoloration.

I conclude our all the wearpad cases either has no oxidations as per below film or acceptable level of oxidation as radiography is accepted.

Thanks.

FOR YOUR REFERENCE ONLY:

NORSOK standard M-601

Regarding Discolaration / Heat tint issues, below are some acceptable oxidation of weld in stainless steel, which is NORSOK standard M-601.

But, still they have shown for butt welds only not for fillet welds, so basically when it comes to fillet welds can be acceptable as there is no through and through butt welding, but just a corner fillet welds.  

AWS D 18.2

Again when collecting information i found some other codes, AWS D 18.2, Guide to Weld Discoloration Levels on Inside of Austenitic Stainless Steel Tube which is (discoloration (heat-tint) criteria for sanitary (hygienic) welds in austenitic stainless steel tube, but as this is sanitary again i coudnt take this is as references, just for your information.

                   _________________

     MOHAMED      MUNEEB      MAHABOOB

 

Date: 2017-05-13 20:11

Sent: Saturday, May 13, 2017 6:10 AM

Subject: Re: Back Purging for fillet welds

 

Gentlemen,

 

Good Morning,

 

Practically, when it comes to long pipes and if we have to purge entire pipe, then the volume of purge according to pipe length might be huge, at the same time for current subject, CSD has recommended for back purge to avoid heat tint issues regardless to any references or failure analysis / case studies. But still it is from CSD.

 

But let us be clear in the requirements, this is just for wear pad or any other more requirements in future (Materials & Types of configurations)? We hope, these amendments will be revised in future standards.

 

Anyhow i leave this to my management upon their final decision.

 

Thanks.

 

Note:

ASME SECTION IX: QG-109 DEFINITIONS, QG-109.1 GENERAL

backing gas: a gas, such as argon, helium, nitrogen, or reactive gas, which is employed to exclude oxygen from the root side (opposite from the welding side) of weld joints.

 

API RP 582, PARA 7.5

Whenever a back purging gas is selected to prevent oxidation or scale formation on the underside of the weld, the purge shall be maintained until at least 1/4 in. (6.3 mm) depth of weld metal has been 

deposited. 

 

 

 

On Thu, May 11, 2017 at 9:09 PM, 

Sent: Wednesday, May 10, 2017 4:54 PM

Subject: Re: Back Purging for fillet welds

 

Noted, this is just my interpretation from code requirements which does not have any precautionary advice even for corrosion for fillet welds.

 

As this is cost effective, i have to be pro-active on these requirements.

 

Anyhow, we will wait for CSD reply.

 

Thanks.

 

Regards,

 

Mohamed Muneeb.

 

On Wed, May 10, 2017 at 8:44 PM, 

 

From:
Sent: Wednesday, May 10, 2017 3:21 PM
To:
Cc: 
Subject: Back Purging for fillet welds

 

Greetings,

 

This is with regards to our discussion for fillet welds purging requirement.

 

This email is not to argue or debate, but just to ensure as per standards / codes requirement and practical understanding of different interpretations and to finalize the precise requirement.

 

As referred, AWS D1.2, D1.6 & D10.6 does not have any such requirements purging fillet welds and also SAES-W-011 itself clearly saying, single sided groove welds which is not fillet weld, continued to ASME SEC - 2 PART C with AWS D 10.11 also saying the same (open root groove / full penetration joint).

 

Moreover, i have copied structural WPS as per AWS D1.6 for your reference, which does not have any back purging requirement for fillet welds and it is approved WPS.

 

Please refer below & advise your opinion on this subject.

 

Thanks.

 

SAES-W-011

11.14 Back purging
11.14.1 An inert backing gas shall be used for GTAW or GMAW root passes on single-sided groove welds for materials of ASME P-No. 5 and higher.

 

ASME SEC-2 PART C

Annex
Guide to AWS Specification for Consumable Inserts
(This Annex is not a part of AWS A5.30/A5.30M:2007, Specification for Consumable Inserts, but is included for information purposes only.)

A6.2 Purging. To provide welded piping systems with
the integrity required by some piping codes, the weld joint
must be a full penetration joint with weld metal of consistently
good quality. One method of obtaining this high level
of quality is the use of preplaced consumable inserts in
conjunction with a specific joint configuration together
with a suitable protective gas back purge. The gas tungsten
arc welding process, either manual or automatic, generally
is used to consume or fuse the consumable insert. This
method is particularly adaptable to conditions encountered
in pipe welding but also may be applied to flat plate type
joints. The main consideration is that a full penetration
groove weld is required when the accessibility is limited
to one side or when the reverse side of the joints is inaccessible
for welding. In order to obtain a suitably smooth,
uniform under side weld surface without crevices or oxidation,
a purge must be established using a suitable protective
gas. Since the second and third passes in the joint may
take the previously deposited consumable insert root pass
above the oxidizing temperature of the base and filler metal,
it may be necessary to maintain the purge until three layers
or 3⁄16 in. (4.8 mm) root thickness is obtained.

 

AWS D 10.11

Recommended Practices for Root Pass Welding Of Pipe Without Backing

2. Preparations for Purging
The highest quality root welds are obtained by using
GTAW either with or without consumable inserts. A purge
(displacement of air at the inside surface of the weldment
with a suitable gas) is required for stainless and nonferrous
piping systems, except aluminum, if a smooth root surface
is to be obtained. Carbon steels and most low alloy steels 
can be welded, using an open root groove, without the use
of an internal gas purge. Purging of joints with consumable
inserts reduces the occurence of defects resulting from oxidation
of the insert. Purging will also increase welding
speed.    

 

 

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