Dear Dr. Mehrdad Rashidzadeh,

I think the following note can help answer your question:

Understanding cast iron and repairing damaged castings permanently by Gary J. Reed at: http://www.locknstitch.com/pdf/gmrc_white_paper.pdf

Best regards, Pierluigi Traverso

solidify your sample at low pressure..

try some secondary heat treatment processes.

By using heat treatment at high temperature

The right repair method depends on the application, the requirements, the dimensions of the casting, the acting stresses and the size of the blow holes. Nowadays SMAW or GMAW welding with a FeNi rod / wire is common practice. I have also received good results with polymer impregnating under pressure. See for example https://www.maldaner.de/metallimpraegnierung/problem-porositaet/ or https://www.diamant-polymer.de/produkte/dichtol/giesserei/. In all cases you need to have qualified personnel.

I agree with Han. GMAW will be better than SMAW.

If the defect sizes are smaller, Impregnation will be better

Welding process has been done before we use acetylene welding method for repairing pipe and fittings but this method have some disadvantages. we are trying to find an alternative method for leakage repairing. for example impregnation but impregnation is not useful and cost effective for large parts. i seen diamant products and we are trying to give a sample from their representative.

another problem is the number of leakage that is acceptable for repairing on water pressure pipe and fittings. there is nothing available in international standards about number of repairs that is acceptable to repair by manufacturer. this is depending on manufacturer.

See ASTM A74 par. 4.5.

There are many different techniques to solve the problem, but first of all you need to know what is this pipe used for (as safety procedure) later on you can deal with it.

Therefore, if the pipe used for gasses or dangerous purpose then you need to follow the right standard, for example ASME B31

Second, if it is used for water or simple use

you can use new technique works like a bandage of different material for the pipe to cover the defects and stop the leakage or you can cover it with a different material sleeve tightened with a clamp

Dear Mehardad,

Blowhole is a cavities defect always located in the cope part of the mould in poorly vented pockets and undercuts. Blowhole is divided into pinhole and subsurface blowhole type. Pinhole is very tiny hole while subsurface blowhole only can be seen after machining. Reason, gases entrapped by solidifying metal on the surface of the casting, which results in a rounded or oval blowhole as a cavity associated with slag’s or oxides. Sand inclusion, sand burning, cold lap or cold shut, misrun, gas porosity, mismatch defects, distortion , thermal defects can occur during welding. Possible causes are due to Inadequate core venting, excessive release of gas from core, excessive moisture absorption by the cores, low gas permeability of the core sand, moisture content of sand too high, or water released too quickly, gas permeability of the sand too low sand temperature if too high, bentonite content if too high and too much gas released from lustrous carbon producer. by reducing this all causes blowhole in ductile iron welding can be stopped.

Remedies

Improve core venting, provide venting channels, ensure core prints are free of dressing, Reduce amounts of gas, use slow-reacting binder and reduce quantity of binder. It is better to use a coarser sand if necessary (soft sand permeability problem), apply dressing to cores, thus slowing down the rate of heating and reducing gas pressure, dry out cores and store dry, thus reducing absorption of water and reducing gas pressure, reduce moisture content of sand, Improve conditioning of the sand, reduce bentonite and carbon carrier content, reduce sand temperature, installing a sand cooler if necessary etc.

Hope it help you out.

Ashish