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RE: [MW:17787] Welding inside CO2 Absorber

By Materials & Welding
Mr. Ratolia,
 
BS 1501-151-28B  is quite old specification. It was later replaced by ,BS 1501-151-430A/430B(see the attachment).This steel is equivalent to SA 516 Gr 60/70.
 
If the design code is Sec VIII, DIV-1, and the maximum section thickness is 38 mm(1.5 inch), then acc to UCS-56 :-

Post weld heat treatment is mandatory under the following conditions:

(a) for welded joints over 11⁄2 in. (38 mm) nominal thickness;

(b) for welded joints over 11⁄4 in. (32 mm) nominal thickness through 11⁄2 in. (38 mm) nominal thickness unless preheat is applied at a minimum temperature of 200°F (95°C) during welding. However  as many of the  fertilizer plants in India are designed as per various process licensor's requirements(e.g MW Kellogg, Haldor Topsoe ..... ) , you need to read through their specifications also.

The default routes would be one of the above:-

  • Draft a weld repair procedure as per  Sec-VIII, DIV -1 as stated above.
                            or
  • Qualify a temper bead weld repair procedure as per NBIC-23, welding method1(No LT requirements ) or welding method-2(LT requirement in original design). A temper bead WPS/PQR should be established as per ASME Sec-IX, QW -290 , following QW-462.12 ,NOMENCLATURE FOR TEMPER BEAD WELDING. 
If the PWHT is mandatory as per process licensor's requirement, then temper bead technique could be a viable option , subject to Code/Specification's acceptance.
 
As BHPV India is the  original fabricator, the advise would be to seek their opinion also. I know they're quite competent fabricators in all respects.
 
I would not advise on drilling and tapping, this would act as stress raisers' with negative consequences.
 
Thanks.
 
Pradip Goswami, P.Eng,IWE
Welding & Metallurgical Specialist
Ontario, Canada
pgoswami@quickclic.net
pgoswami@sympatico.ca
 
 __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
 On Thu, May 23, 2013 at 2:06 PM, B M Ritolia <bmritolia45@yahoo.com> wrote:
Dear All
We are having Co2 Absorber in our Ammonia plant. This equipment has been installed in 1969. The MOC of vessel is BS 1501-151-28B & is 38mm thick. Now we want to install a new modified demister set on the top of the tower. In this connection demister manufacture wants to weld a
supporting ring (10 MM thk 516 Gr. 70) and 4 nos. brackets (516 Gr. 70). As per supplier, the brackets are to be welded at top conical portion 38 mm thk. (90 Degree orientation) of the absorber. After this 10 mm thk supporting ring is also to be welded to the absorber shell.
As per the drawing of CO2 absorber, the vessel supplier M/S BHPV India have mentioned under the Note;
'NO WELDING IS TO BE DONE ON THE VESSEL AFTER HEAT TREATMENT UNLESS OTHERWISE PERMITTED BY CODE/SPECIFICATIONS".

You are requested to kindly advise regarding welding of 04 nos. brackets and supporting ring (10 MM thk 516 Gr. 70) to absorber shell (38 mm thk. BS-1501-151-28B).kindly also advises welding procedure and type of electrode to be used.

Alternately can we fix the bracket by 8mm dia bolt (4 nos per bracket) after drilling & tapping in the vessel & welding the ring with the bracket? Will it affect the design criteria of the vessel?

Thanks & Regards,

BM Ritolia
Advisor
Kanpur fertilizers & cement ltd.
Udhog Nagar,Panki ,Kanpur
Uttar Pradesh,208022 India
Mob. 07388003288
Land Line 0512-2693504

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