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Participant

Join Date: Jan 2011
Posts: 4

Preheating of Weld Joints

04/24/2012 4:27 AM

In my project some joints of ASME SA 335 P11 pipe material were welded with out preheating. The pipe size is 1" and they were socket welds. The client is demanding to cut the welds and to do rewelding. But as per my knowledge preheating is done to avoid Hydrogen induced cracks in HAZ, and rewelding is not a remedy for the issue. What can be the exact rectification?

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Guru

Join Date: Jan 2010
Location: Mineral wells Tx
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#1

Re: Preheating of weld joints

04/24/2012 5:16 AM

Normally we don´t Preheat P4 under 19mm. Over 19mm we use 120º to 150ºC (Torch). Try to use an RT random (5%) to verify the required GAP and make full hardness test. Maybe enough for your client. Cut and Re-welded can be Harmful. WP

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Power-User

Join Date: Dec 2010
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#2

Re: Preheating of Weld Joints

04/24/2012 12:04 PM

Socket joints for 1" size pipe in SA335 P11 do not need pre-heat. Even radiography will not be of much help. It seems that you do not have approved WPS and ref. PQR, but you can reffer some PQR relevent to this material and this type of joint from some other project to convince your client. Cutting and re-welding is not the solution.

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Guru

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#3

Re: Preheating of Weld Joints

04/24/2012 8:23 PM

preheating is used to prevent stress fractures from sudden temperature changes. annealling by slowly cooling the weld with heat "a torch" would be approppriate on a small pipe.; block both ends of the pipe in order to maintain welding temperatures.

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Active Contributor

Join Date: Feb 2011
Posts: 12
#4

Re: Preheating of Weld Joints

04/24/2012 11:51 PM

NO NEED FOR PREHEAT REFER PROCESS PIPING ASME B 31.3 TABLE 330.1.1 PREHEAT TEMPERATURES IT SAYS P11 MATERIAL MINIMUN AND MAXIMUM TEMPERATURE FOR ALL THICKNESS ONLY 10 DEGREE CEL.

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Guru

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#5
In reply to #4

Re: Preheating of Weld Joints

04/25/2012 12:37 AM

you can spout all the specs you want too. will it pass the test is the question.

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Power-User

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#9
In reply to #4

Re: Preheating of Weld Joints

04/25/2012 12:36 PM

P11 type Cr-Mo steels are air hardening steels and undergo micro structural transformations that depend on the rate of cooling from above the upper critical temperatures.The mechanical properties are dependent on these transformations..

With faster cooling rate, strength,and hardness increase and ductility is reduced. However, because of lower carbon content (0.15 % maximum) carbides are present in limited amounts and the results in higher ductility at any given strength level than obtained from high-carbon steels.

When the steels with 2,25Cr - 1% Mo and above get heated above their transformation temperatures in operations like rolling, forging, hot forming, welding etc., with consequent loss in ductility and toughness due to their air hardening characteristics, they require further heat treatment, to restore these useful mechanical properties. Lack of Pre heat and post heat treatment may produce cracking in the weldment.

For 1/2 Cr-1/2 Mo. recommended pre heat temp. is 500C up to 13.0 mm thickness. For 1 Cr-1/2 % Mo & 1.25Cr-1/2% Mo, it is 1200C for same thickness. Hence, if they are not pre heated, it may not create much problems. The temperature would have reached up to that level during welding. A NDT and hardness check may give you an indication to you towards its quality.

Still the joints can be post weld heat treated at 600-7200c if required (or) insisted up on. A post NDT may may be done if needed later.

sridhar.

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Active Contributor

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#6

Re: Preheating of Weld Joints

04/25/2012 1:24 AM

ASME SA 335 P11 pipe material coming under base metal metal P.No-4. as per asme b31.3 process piping table 330.1.1 preheat temperatures, p4 material thickness all minimum temperature 149 deg cel. better you have to cut and preheat and then weld.

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Commentator

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#7

Re: Preheating of Weld Joints

04/25/2012 9:17 AM

What are the Project Speifications and Codes ?

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Guru
Engineering Fields - Piping Design Engineering - New Member Egypt - Member - Member since 02/18/2007

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#8

Re: Preheating of Weld Joints

04/25/2012 11:37 AM

The pipe material ASME SA 335 Grade P11 (1.25 Cr, 0.5 Mo) has a P-Number 4, and has SMYS of 60 000 psi and as per ASME VIII, Div.1, Nonmandatory Appendix R "Preheating" shall be as per Para. R-3 for P-No. 4 Group Nos. 1 and 2:

(a) 250°F (121°C) for material which has either a SMYS in excess of 60,000 psi (410 MPa) or a thickness at the joint in excess of 1⁄2 in. (13 mm);

(b) 50°F (10°C) for all other materials in this P-Number.

Since the pipe wall thickness less than 13 mm and SMYS not in excess of 60 000 psi, so preheat shall be at 50°F (10°C).

Important Note. Preheating is done not only to avoid hydrogen induced cracks in HAZ, but also to control cooling rate of weld puddle during its solidification, where without preheating there will be a rapid cooling rate due to rapid sinking of heat by pipe body adjacent to weld which causes solidification of weld sides and middle of weld remain at molten phase which causes cracks.

And when you apply preheating before welding, there will be a control of heat transfer which will lead to proper mechanical properties of material.

My point of view is to check the welds for existance of cracks by any method of NDE like RT, UT, MP, etc. and if you find any cracks, you have to cut and reweld.

...............................................

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#10

Re: Preheating of Weld Joints

04/25/2012 5:31 PM

In your post you have stated "SOME joints of ASME SA 335 P11 material were welded with out preheating", i think the question is what did the customer ask for what were the specifications you were given for the job. If you followed them no problem if you didnt well the customer should expect to get what they pay for.

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Abdel Halim Galala (1); durtieduck (2); Grochy (1); Mechanicalmark (1); Mukesh0861 (1); SRIDHAR (1); thangaraj762005 (2); Whitephone (1)

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