CRACKS IN SKIRT WELD

[Lassaad]

Dear Expert,
We are facing some problem consisting of some little weld cracks that appreared after PWHT.
These cracks are within joint between thé LPG Sphere (4000 Cum) and its settling skirt.

As i remembrer in ASME VIII, repair of thèse cracks Could be done and only local HT Will be required.
Our client confirmés that as per CODAP 2005, thé HT after repair should concern thé concerned joint in all the sphere circonference, which is a real big problem.

Please share your expérience in similar cases.

BR


Sent from my ThinkPad S230u

[pgoswami]

Hi Lassad,

 

Head to skirt weld joint is one of the complex weld joints in any pressure vessel. In addition to hoop stress from the resultant pressure there's constant dead weight load of the vessel/equipment on the head to skirt weld. If the vessels are subjected to cyclic loading shirt welds could fail prematurely.

 

Attached are 2 schematics on head to skirt welds. The first one a fillet weld is commonly used, while the second design is recommend for better design and integrity. Which design was used for the LPG spheres ?

 

If the cracks are removable by grinding and blending then that should be the first option. Following removal perform WFMPI of the weld seam  to ensure no cracks are left behind in addition to the ones removed.

 

If it calls for deeper grinding and weld repair, there the rules of the respective design codes should be followed. Head to skirt weld would require same or more care than the  girth welds, in terms of preheating , interpass temperature control etc.

 

If PWHT following weld repair is  required by the design code that such PWHT should be  on the total circumferential welds or as accepted by the AI.

Local or spot PWHT could create distortion. However for C-Mn steel as PWHT(SR) is usually done well below the AC1 temperature(723 Deg C)there are a number of ways to control the distortion.

 

Thanks.

 

Pradip Goswami, P.Eng,IWE

Welding & Metallurgical Specialist

Ontario, Canada

pgos...@quickclic.net

pgos...@sympatico.ca

 

              

---

From: Lassaad Mokrani [mailto:lassaad...@gmail.com]
Sent: Monday, December 23, 2013 3:03 AM
To:  pgos...@quickclic.net 
Subject: Fwd: CRACKS IN SKIRT WELD

Dear Mr.Pradip,

Could you please give me your valuable inputs on that matter?

Many thanks

--

Meilleures salutations

MOKRANI Lassaad

Consultant Civil Engineer

Tunisia

00216 20 649 755
http://www.linkedin.com/pub/lassaad-mokrani/16/364/907


















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