acpl_sefi
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Joined: 26 Jan 2003
Posts: 63
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 Posted: Thu Jul 21, 2005 12:04 amPost subject: Welding of steel |
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Dear all,
I want to know-- what is the size of weld deposited on a pair of rebars being welded together in relationship to the weld electrode size. COnsequently what should be the length of lap (is there a minimum). Is this a prequalified weld as per AWS or any other standard. If more than one pass is required for welding (say 5mm electrode on a 25 dia bar) what are the precautions to guarantee the strength of the weld (3 passes etc.)
Regards
Vipul Ahuja
On Sat, 16 Jul 2005inchak@tatasteel.comwrote :
| Quote: |
*************************************************
SEFI e-Conference on Steel Reinforcement from June 27 to July 17, 2005
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Sponsored by TATA Steel
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Thanks for a very topical set of questions.
I proceed to briefly answer each one to the best of my ability.
1) Can normal HYSD bars and TMT bars be welded.
Answer: Welding is permitted and, indeed, carried out. The proposed draft
revision of IS: 1786 (available in the URL:
http://www.bis.org。in/sf/ced/p_7303.pdf) brings more clarity to this
subject. I quote the relevant clause
QUOTE
3.2.2 For welding of cold-worked deformed bars, the recommendations of
IS 9417:1979� shall be followed.
NOTE - Till such time IS 9417 is revised to incorporate the requirements of
Thermo-mechanically treated steel, the recommendations of IS 9417 shall
also apply to
thermo-mechanically treated steel with the provision that the temperature
under clause
10.3.4 of IS 9417:1979 shall not exceed 200 Deg. C for subsequent beads.
UNQUOTE
While this is going to bring complete clarity on this subject, we do not
see the need to maintain an inter pass temperature of 200 Deg. C. TMT is
tempered at a temperature of 550 deg.C or more and is stable with respect
to mechanical properties at least upto that temperature. Rather HYSD bars
(CTD?)attain their strength by cold working and are susceptible to losing
their strength beyond 400 deg.C.
As a result, whatever welding parameter is good for CTD will be good for
TMT as well. An attempt is on to get this suitably incorporated in the
undergoing revision of IS:1786 specification.
2) If welded is permitted, what happens to steel due to heat treatment and
what stress should be considered in design.
Answer: If welding electrodes of matching strength is used, there is no
loss of strength because of welding. However, the prevailing provisions of
IS 456 need to be complied with.
QUOTE
26.2.5.2 Strength of welds
The following values may be used where the strength of the weld has been
proved by tests to be at least as great as that of the parent bar.
a) Splices in compassion - For welded splices and mechanical connection,
100 percent of the
design strength of joined bars.
b) Splices in tension 80 percent of the design strength of welded
bars (100 percent if welding is strictly supervised and if at any
cross-section of the
member not more than 20 percent of the tensile reinforcement is welded).
UNQUOTE
3) Some Steel companies claim their bars can be welded, what is their
composition / speciality
Answer: Again one needs to address this question within the boundaries of
IS: 1786. Note 1 of clause 3.2 (page 6, stipulates :
QUOTE
For guaranteed weldability, the percentage of carbon shall be restricted to
0.25 percent, maximum.
UNQUOTE
Further Amendment No. 2 of May 2002 says
QUOTE
Note 1 - For guaranteed weldability, the Carbon Equivalent using the
formula ............ shall be not more than 0.53 percent, when micro
alloys/low alloys are used. When micro alloys are not used, Carbon
相当于使用公式 ...........应not more than 0.42
percent. Reinforcement bars/wires with higher Carbon Equivalent above 0.42
percent should, however be welded with precaution. Use of low hydrogen
basic coated electrodes with matching strength bars/wires are recommended.
UNQUOTE
4) Welding is a common practice in Piles and heavy engineering such as
bridges etc.
Answer: YES. It is also quite safe and extensively used abroad. We should
have no hesitation in adopting this practice wherever it can add value.
Hope you find the responses in order and satisfactory
Thank you once again
Indranil Chakrabarti
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