Martin,
The only way if control the O2 level. Less than 0.05%
The back purge for stainless steel and nickel alloys shall reduce the oxygen level below 0.05%. An oxygen analyzer should be used to determine the oxygen content inside the pipe during purging.
Sure G48 will pass.
With Kind Regards,
S.Elumalai.
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Martin Prad
Sent: Thursday, December 29, 2011 9:58 AM
To: materials-welding@googlegroups.com
Subject: RE: [MW:13358] RE: 13349] Oxygen level in purging gas during welding of duplex stainless steel
Dear Goswami,
Thanks for your detail email as always. A pitting corrosion test to G48 shall be carried out. I am afraid a test reslut can not pass in the root part. Just looking a best practical solution what % of gas mixes is best to use as purging. There is an Oxy Monitor from Weld-Tech (Finland Company) to monitor the O2 level in purge gas. I will try to summirize your below reccommendation to use on this occasion.
Very kind regards,
Martin.
From: pgoswami@quickclic.net
To: materials-welding@googlegroups.com
Subject: [MW:13352] RE: 13349] Oxygen level in purging gas during welding of duplex stainless steel
Date: Wed, 28 Dec 2011 17:44:09 -0500
Martin,
Nice to hear from you after quite a while..I have come across this question in the past while qualifying procedures for duplex S.S, on the strict requirements of oxygen, in purge gas. Please see below the extracts/recommendations of consumable manufacturers, and the general design practices from API and as well as the technical specification of an oil major. The API recommended practice and duplex/super duplex S.S product manufacturers recommendations is between 2500-5000 ppm of oxygen in the purge gas. Note the general guidelines do not always address the most stringent requirements.
For the clients in the oil and gas production industries the requirement is typically 50 ppm or below for the (typically offshore applications)..My feel is that, it's difficult to pass the pitting corrosion test (G-48) without such strict control on the level of oxygen. However literatures suggests that a proper purging gas can be effective at higher level of oxygen in the root pass. Depending on the residual level of oxygen one can get various levels of discolorations in the weld root (see the attached document, welding.pdf). However for offshore applications I would feel the requirements are very cut throat due to the reasons mentioned above.
I've attached an extract from Avesta Welding Manual , it also calls for 50 ppm max of O2.
If both the specification applies for the same project, then you need to discuss with the client about discrepancies. Could you please specify:-
- From O2 level of 5000 ppm, what're the additional testing requirements over and above ASME Sec-IX
- For 25ppm allowable oxygen h=what're the weld testing requirements in the coupon?
If you could post some updates later it would be appreciated.
Thanks.
Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist & Consultant
Ontario,Canada.
Email-pgoswami@sympatico.ca,
Examples:-
1. API 938C-C.2.4 All single-sided welds shall be made with a GTAW root pass and back purged until at least 1/4 in. (6 mm) of weld metal thickness has been deposited. Backing gas shall be welding grade 90 % nitrogen/10 % hydrogen mixture, pure nitrogen or argon/nitrogen mixture with not less than 5 % nitrogen. The oxygen content of the back purged volume shall be less than 0.25 % (2500 ppm). The seller shall submit details of the method and equipment to be used for monitoring oxygen content as part of the WPS. Shielding gasses can be argon or argon with 2 % maximum nitrogen.
2.WEIR MATERIALS, Guidelines for Welding, ZERON 100
Back Purging:- When welding Zeron 100, it is recommended that commercial purity argon is used to displace the air behind the joint. The oxygen content of the resulting argon/air mixture must be monitored and controlled to ensure that sufficient nitrogen is retained in the backing gas “mixture’ in order to inhibit loss of nitrogen from the weld pool. In practice the oxygen level of this mixture should be controlled at approx 0.5% (5000ppm) oxygen monitored at the start of the welding sequence. In this way, a positive partial pressure of nitrogen is maintained behind the joint thus preventing nitrogen loss from the root bead, whilst the oxidation produced remains acceptable. Passes subsequent to the root pass can be made with minimum oxygen contents.
The backing gas composition should be monitored at the joint line using a portable oxygen monitor immediately prior to starting or re-starting welding in order that consistency can be maintained. Adhesive tape low in sulphur and chloride is used around the open joint seam, and the tape should be removed progressively during the welding sequence.
3. Metrode:-Duplex & superduplex ferritic-austenitic stainless steels
Purging
A gas purge must be used for root runs deposited using the TIG process and will normally be maintained for the first three layers or approximately 10mm of deposit. Commercially pure argon is generally used as the purge gas. Purge flow rates are determined by the pipe size but it is important that following the removal of tacks, grinding etc that the purge is allowed to stabilize again before welding. The efficiency of the purge should be monitored with an oxygen monitor to ensure the oxygen content is maintained below 0.5% (5000 pap) oxygen.
4.0 Worldwide:- Oil and Gas Major
During welding, DSS shall be protected from oxidation by providing a shielding purge on the inside with the same composition as the shielding gas for welding. The purge gas shall replace all air. No welding shall start until the oxygen content has dropped to below 50 ml/m3(i.e 50 ppm). During welding the root run, there may be a surge when welding is started and welding shall be stopped if this surge goes higher than 500 ml/m3. This shall be measured with an oxygen analyzer, capable of measuring oxygen contents between 0 and 1000 ml/m3.
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Martin Prad
Sent: Wednesday, December 28, 2011 2:56 AM
To: materials-welding@googlegroups.com
Subject: [MW:13349] Oxygen level in purging gas during welding of duplex stainless steel
Hi friends,
I have 2 different specification which the requirements are different for the oxygen level in purging gas during the welding of super duplex pipe.
One of them calls for 25 ppm (0.0025%) another one calls for 5000 ppm (0.5%). Could you please shed some light on this as which one is up to the standard with references?
Thanks,
Martin.
--
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
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.
--
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
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.
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
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.
******************************************************************************************
CONFIDENTIALITY NOTICE
This e-mail and any attachment are confidential and may be privileged or otherwise protected from disclosure. It is solely intended for the person(s) named above. If you are not the intended recipient, any reading, use, disclosure, copying or distribution of all or parts of this e-mail or associated attachments is strictly prohibited. If you are not an intended recipient, please notify the sender immediately by replying to this message or by telephone and delete this e-mail and any attachments permanently from your system.
No comments:
Post a Comment