Backing strip

[prem nautiyal]

Hello friends   Need expert opinion on the subject as follows..   A Heat exchanger is being fabricated as per ASME Sec VIII Div.1. The Channel Shell and dish end thickness is @ 10mm and dia. @ 600mm. The MOC is SA516 Gr.70. Now for the closing joint seam i.e. Channel Shell # Dish end (single V joint) can a "Permanent Backing strip" with 8mm root gap be used ? The permanent backing strip will be 6mm thicknes X 25mm wide and stich fillet welded from inside. Contractor has submitted WPS mentioning permanent backing strip for this joint. Can we accept this ? Is there any provision in code for non-usage of permanent backing strips in pressure parts ? The joint calls for full radiography. Contractor claims that upto 10mm thickness the RT will be cleared. Can we accept this case as per ASME Sec.VIII Div.1.   Regards   Prem Nautiyal

[gopuna...@yahoo.com]

ASME Second VIII Div 1 permits use of backing strip for the type of joint in question. Please refer para UW-12 for joint efficiency.

But why the contractor is not prefering a single side full penetration joint configuation or even a double welded butt joint. Welding from inside is not a big issue for 600 dia shell.

RT with backing strip in position may be a bit tricky and interpretation problematic due to slag entrapment between shell and b/s.

Gopu

Sent from BlackBerry® on Airtel

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From: prem nautiyal <prem_na...@yahoo.com>

Sender: material...@googlegroups.com

Date: Tue, 20 Mar 2012 00:19:33 -0700 (PDT)

To: <material...@googlegroups.com>

ReplyTo: material...@googlegroups.com

Subject: [MW:13932] Backing strip

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[prem nautiyal]

As i have mentioned earlier, the joint is a closing seam with no access from other side, hence can't be welded from inside. Also the contractor does not want to take risk of any RT repairs with his qualified welders by welding a single sided FPW.   However as the root run and hot pass are going to be welded with TIG , there will be no chances of slag entrapment in root run between metal backing strip and shell/dishend.   Considering Spot radiography as per UW-12, the issue is now cleared.   Regards   Prem Nautiyal --- On Tue, 3/20/12, gopuna...@yahoo.com <gopuna...@yahoo.com> wrote:

[Prakashraman B]

Please check your client specification.

Some of the equipments in petrochemical / refinery / Power services specify that no backing strip shall be used.

 

Prakash Raman .B

 

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[Gopalakrishnan G]

Dear Expert

can you suuguest what type of elecrodes to used for Sa-516 gr 70 shell to Dish (Dia 610 mm) inorder to get good penetration. preferably for SMAW process

 Material : sa 516 gr -70

Thickness : 10 mm (Shell) to Dish (12 mm)

Process : SMAW

Code : ASME Sec Viii

[Mahantesh Loni]

Root by tig with ER70S-2 and filippo by E7018

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[prem nautiyal]

Use basic coated Low Hydrogen electrode E7018 / E7018-1.

[Gopalakrishnan G]

Thank you for kind advice. other than TIG whether I can use E-7010 for root? .Because my shell dia 610 mm inside grinding is difficult .

--
G.Gopalakrishnan
Welding Engineer
Mukand Ltd
Mumbai
Moble :+91-9833397917

[Mohit Aggarwal]

If there is manhole then from inside welding can be done but.it will take longer time and all arrangements for welder shoul be there i.e. Ventilation and fan etc...

Best Regards,
Mohit Aggarwal.

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[pgoswami]

Hi Prem,

 

Backing  strip joint (on the channel side) certainly  does not  reflect any good engineering judgment. Usually in an exchanger, Tube sides(channel) always contain more corrosive fluid with higher velocities. A  permanent  backing strip joint could be just the beginning of all sorts of trouble in service, e.g, crevice corrosion, erosion/cavitation or other forms of flow induced damages also.

 

I am not sure why this joint can't be changed to a single sided Full Penetration joint by all means. A backing strip joint has  less joint efficiency (0.85) as compared to an FP groove weld. In that case the design thickness would change @ this joint.

 

Contractor gets their money once the equipment is fabricated. However the owner has face all the resultant music for many years to come.

 

Hope this answers your query?

 

Thanks

 

Pradip Goswami, P.Eng,IWE

Welding & Metallurgical Specialist

Ontario, Canada

pgos...@quickclic.net

pradip....@gmail.com

http://ca.linkedin.com/pub/pradip-goswami/5/985/299

 

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From: material...@googlegroups.com [mailto:material...@googlegroups.com] On Behalf Of Mohit Aggarwal
Sent: Friday, August 08, 2014 3:29 PM
To: materials-welding
Subject: Re: [MW:21589] Backing strip

http://www.linkedin.com/groups/MaterialsWelding-122787?home=&gid=122787&trk=anet_ug_hm

 
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.

[Pankaj Dahiwadkar]

Hi, You can use E7016 electrode for root purpose if you are looking for one sided root penetration joint. Kind Regards, Pankaj Dahiwadkar +65-9770 5000 Sent from Yahoo Mail for iPhone

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From: Gopalakrishnan G <gopa...@gmail.com>;
To: material...@googlegroups.com <material...@googlegroups.com>;
Subject: Re: [MW:21588] Re: Backing strip
Sent: Fri, Aug 8, 2014 1:31:59 PM