SA 299 vs ASTM A-36

[julian23]

in my company we have a problem in the steam drum of the recovery boiler. Because of an accident we have to repair many times cracks on the surface and between the holes. A solution proposed by a foreing company was to change o piece of de afected area by welding. They propoused to replace the SA 299 material (original) with a new piece of the same dimentions of ASTM A-36 material. Is the propousal correct?? wouldn´t we have problems with the welding of the two materials. I wil apreciate your advices.

 

[stanweld]

If the item is subject to ASME PV Code and subject to the NBIC for repairs, ASTM A-36 may not be used for replacement of a pressure part. In addition, replacement of a higher strength material with a lower strength material cannot be done without Alteration calculations.

What is the operating temperature of the drum?

 

[metengr]

ASTM A 36 is not suitable as steam drum material and would not be permitted by ASME B&PV Code. Before considering any material or even weld repair one needs to understand what is causing the damage. If this is ligament cracking, which I suspect, this is related to operational practices and this must be addressed. You mentioned accident, what happened?

 

[julian23]

Thanks for replies. Standweld the average temperature in the steam drum is 250 ºC. I need information to reinforce the position of "not using ASTM A36". The incident was that the drum almost stay without water during operation because one of the generating bank tubes had loosen. This caused the cracks (also ligament ones) and the weakening of the material. Several inspections and weldings have passed but now the cracking area is bigger so we decided to change a segment and one company offers to change the piece using ASTM A36.

 

[metengr]

So you had a lower water level in the drum and subjected it to a large thermal stress gradient. The material is not metallurgically damaged; it can be weld repaired with no adverse affect on future reliability of the drum. I would bet this happened several operating cycles.

Please refer to ASME Section VIII, Div 1, Part UCS, paragraph UCS-6.

 

[stanweld]

Per ASME II Part D SA-36 is not permitted for ASME I manufactured items but is for ASME VII, Div. 1 at temp up to 650 F (343 C). If either of these Codes apply to your drum, the material must be ASME SA-36. As previously stated, the repair is an Alteration under NBIC and the required thickness for the weaker material must be calculated. The difference in thicknesses may be detrimental with regard to thermal fatigue, especially with past operating history. If T is such that PWHT is required, that is another consideration and if T less than or equal to 1.5" SA-36 may not be fully deoxidized. Finally as metengr stated, repairs can readily be made by welding only.

 

[vpl]

Stanweld, you managed to confuse me (and no comments about how easy that is to do!). So for ASME I or II, SA-36 is a NO but for ASME VII(Recommended Guidelines for Care of Power Boilers) it's MANDATORY? What about ASME VIII (Construction of Power Boilers), where there's a possibility this guy is working?



Patricia Lougheed

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[stanweld]

vpl,
I did not mean to imply that SA-36 is mandatory for vessel pressure parts; only that it may be used in ASME VIII, Div 1 pressure parts construction ,as plate, up to a temp of 650F. The plate material may not be ASTM A-36; it must be SA-36. They could effect the repairs with SA-515 Gr 70 or SA-516 Gr 70 which has a greater design allowable stress and would mitigate the potential thickness difference between the lower strength material and the SA-299 material.

 

[metengr]

In other words there was a typo - the reply by stanweld should have stated Section VIII, Div 1, not VII.

 

[vpl]

Thanks stanweld, that makes it clearer. Hopefully, it also clears up any confusion for the OP as well.

Patricia Lougheed

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