TACK WELDING ON STEAM DRUM 2

[hyl]

Hello members
we have chemical cleaning we need to close the down commer inside the drum (size 40cm )can we use simple tack weld to support the closer .please advice us .
thank you very much and god bless.

jamil a alshahed nama
hartha power station

 

[metengr]

For a blind flange?

 

[saplanti]

I would not weld on the drum shell plate at all. It is too dangerous. I would do blanking at the lowest location of the downcomer instead if there is no other way for chemical cleaning.

Isn't there a vortex breaker at the outlet to the downcomer? If there is not, you may weld a blank inside the downcomer pipe by checking the material of the downcomer. Sometime we use a transition material between drum material and the downcomer pipe material. You should not weld onto the drum and transition material if available. Mostly the downcomer material is A106B. However the downcomer diameter is big therefore you may have low alloy downcomer material if the pressure is large. So, you need to check the downcomer material as well. I assume that the downcomer material is A106B, you may weld the blank on it. However removing the blank may/may not require heat treatment. You need to consult a metallurgist or some experts can comment on that. I guess the treatment is related to the thicknesses of welded members and the chemicals used in the drum during the operation. I suggest you to use minimum heat input during welding.

In case there is vortex breaker in line I suggest you to cut short length of downcomer by watching the transition material if available and downcomer supporting system. Then blank it for the process you need to progress.

Hope it helps,

Ibrahim Demir

 

[InTheField]

Are you only chemical cleaning the boiler drum? This is not a typical cleaning if you are. Deposits located in the drum do not reflect the amount of deposits in the remainder of the boiler.

Has there been a sample tube taken from the high heat zone (ie. burner zone) and a DWD (deposit weight density) analysis completed (you will need an amount of deposit per area and the analysis of the deposit to have an effective chemical cleaning completed).

All that being said - if you just need a cap on the downcomer to prevent material from falling down during a post chemical clean inspection you do not need to tack weld it in place. Just have an oversized plate to cover the hole with keeper bars welded to the back side of the plate to keep it from sliding.

If you really want to tack weld it to the drum take a look at NBIC requirements for preheat. Internals are welded to the drum all the time (drum material is usually SA 516 or 517 - it's been a while so don't quote me on that). If you are welding to the downcomer material there is likley no preheat requirement, however i would preheat it anyway (again refer to NBIC). Note that NBIC may just point you to ASME Sction I.

Again - my main question is are you only cleaning the drum?????

I know this post is a little after the fact, but hopefully better late than never.

 

[hyl]

Hello MR inthefield

Thank you very much for your advice it is very usfuel for me .my dear i want to inform you that the chemical cleaning of the boiler is for complete boiler (660T/H)capacity .according to the chemical cleaning procedure the down comer must be close and the chemical is feed to the drum and the flow of the chemical is reversed from the drum to the riser and after to the side walls header and tubes and then from bottom header to the drum by chemical cleaning pump the operation continue according to the chemical analysies . scale density is (45mg/cm^2) and we take sample from the heat zone before and after the chemical cleaning...thankx and god bless

jamil a alshahed nama
hartha power station