Pitting acceptance criteria

[Gulam kader]

Dear all,

 

We received one 40" elbow (ASME 16.9) ASTM A 860 material having so much pitting on full external surface. Which standard we can refer for the acceptance criteria? 

 

 

I referred in ASTM A 860, its talks about only depth of surface discontinuity(5% of the nominal thickness),  there is no detail about the area of the pitting allowance.

 

Please help me on this issue. Very urgent

 

Regards,

 

Gulam Kader 

[K.Babu]

Hi,

 

This topic has been discussed several times.

 

Neverthless, there is no spec. for the pitting acceptance.

 

Since the ultimate effect of the pitting is, reduction in thickness, we can apply the thickness tolerence.

If u refer ABS Modu 2008 , they have mention 0.3 mm in thickness reduction, so max. pitting depth is 0.3 mm as per ABS Rules.

 

 

 

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Thanks & regards,

K.Babu
Welding Engineer, 
Singapore

[narasimha murthy]

You need to consider the design thickness requirements for the particular line, which includes the corrosion allowance too. Based on the requirement you may decide whether the pipe can be used.

 

Regards

 

J.N.Murthy 

[michael lawrence]

dear sir anything biger than the calaberation notch wich is 1mm is a defect and i do believe it would be down to the welding engineer to make a desision as to wether or not to use the elbow i do bilieve that there is no specific area as to how much pitting would b allowed the decision would be yes or no or can the pitting b eliminated i.e repair welded as a welding inspector i would have some idea as to wether or not it way be used but would hafto come from a engineer and depending on what product would be going through the material

 

 

regards

mike.

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[daniel iordache]

Hello 

the better way about pitting analyze and to get a right decision is to contact a corrosion engineer to evaluate area according with visual and ultrasonic testing report- he will calculate base on remaining thickness, length, material spec, operation pressure, safety factor the corrosion allowance and the remaining strength of material for corroded subject (api 31G).....other is to calculate all above according API 579.....

regads

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Daniel Iordache
Bureau Veritas - Angola
Mechanical& Welding Surveyor
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[Darcy Morin]

Usually the material specification will require that a minimum  of 87.5% of the ordered nominal wall thickness be maintained. This can be verified by blending and baseline UT. One other requirement is the "workmanlike finish". This is a subjective judgement. In either case, if buildup is required, ensure that your organization is certified to repair fittings and perform welding in accordance with approved WPS.