Pump Casing Castings

[Rob100]

I had posted the below in the Mechanical forum yesterday and have recieved no responses. Any help here?
I am reviewing specs for pump units for a water system. These are city water (potable water) and approx 50 mgd pumps. The casings are specified as DI or CI. Is there a quality standard for porosity and integrity of the casing? This is not a critical application so I don't think that I can probably use visual inspection methods. I am tying to define void size or porosity. Also, if the casing is cracked, I don't want this to be welded and ground unless I know the procedure and stress relief.
Also, the impellers are cast stainless steel. I have the same concerns.
Hopefully there will be no problems but I want to cover my bases if there are

 

[metengr]

Rob100;
Do you know the ASTM Standard specification for the castings?

Here is what I would recommend; search on the Internet for the following information

"Steel Castings Handbook, Supplement 2" from the Steel Founders Society of America.

I believe I had downloaded my copy free. Review it for basic information regarding ASTM material specifications for castings.

The American Water Works Association (AWWA) might contain information on casting quality requirements. I did not check for this information.


If you inspect the pump castings, I would recommend a volumetric method like radiographic testing (RT). The following ASTM Standards would be applicable to you;

ASTM E94
ASTM E186 or E146 for heavier wall castings.

Regarding defect acceptance, if the AWWA does not provide guidance, you are on your own for specifying defect type and severity level for this application.

What type of cast stainless steel are the impellers?

 

[EdStainless]

Rob, you are on the right track. Look at the ASTM specs involved and see what is there already. You will need to use sources such as the SFSA guide to set defect size limits. You should set max defect size and quantity.
Visual should be fine.
You might think about X-ray for flanges or other loaded parts.
Requiring repair procedures is fairly typical also.


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[SJones]

MSS SP-53, 54, and 55 may be of some use as will ASTM A834 as a starting point.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[Rob100]

Thank metengr. The castings are noted as cast iron ASTM A278-Class 30; ductile iron ASTM At36 Grade 64-14-12, or ASTM A395; Cast Steel ASTM A27 Class 65-35 or A216 Grade WCB.
Stainless Steel impellers are ASTM A743 CA15.
AWWA was somewhat generic in their specification. I was hoping for something a little more difinitive. I will look at the ASTM you noted for RT.
EDStainless: xRay is a bit expensive but I may be forced into it. Thanks.
SJones: I have never used ASTM A834. I will need to get a copy of that one. Are MSS SP-53, 54, & 55 a visual inspection. I didn't think these quantfied the inspection. Thanks.

 

[pwtomlin]

If you're looking to specify an acceptable level of porosity, aren't you pretty much forced to rely on something beyond visual inspection? I work in a steel foundry, and while I don't know a whole lot about the QC side of things I don't think we generally do much beyond a visual inspection for parts that will see relatively tame service. Of course the customer can always specify more but in most cases they don't want to pay for it.

 

[pwtomlin]

As for visual inspection, MSS SP-55 and ASTM A802 are the standards we typically use.

 

[EdStainless]

I used to work in casting some large bolted-bowl pumps. If we were doing large units we would x-ray the flanges. For smaller units we didn't bother, visual only.

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Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[arunmrao]

I do not have much to add at this late stage. Pump casings in grey iron or DI are usually sound and pressure tightness is not a major issue. The neck region might need to be checked for any sweating. It is not advisable to carry out any weld repairs on the castings as the alloys are amenable to crack. Any defect will get revealed during machining. Radiography is expensive and not commonly adopted.A good foundry should be capable of giving you a good quality castings.

In the case of stainless steel impellers most of them are simple ,radiography can be done of necessary , and they can be easily repair welded. Importance should be given to flow path in the impeller.Try to use impellers made using ceramic cores. These will give a clean internal surface with no gas defects or sand inclusions.

I am providing a few references . Also if you can visit the links for grey iron and ductile irons a wealth of information is available.


E1030-05 Standard Test Method for Radiographic Examination of Metallic Castings

E802 Reference Radiographs for Gray Iron Castings Up to 4 in. [114 mm] in Thickness

E689 Reference Radiographs for Ductile Iron Castings

A743/A743M-06 Standard Specification for Castings, Iron-Chromium, Iron-Chromium-Nickel, Corrosion Resistant, for General Application


ASTM A536-84(1999)e1
Standard Specification for Ductile Iron Castings

http://www.ductile.org

http://www.ironcasting.org

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[Rob100]

Thanks. Since I started this, I have inspected 3-18" diameter castings for the bowls on vertical turbine pumps and have found pin holes and cracks. My experience shows pin holes can grow to large air pockets once machining starts. The cracks are poor foundry practices or other damage. My challange now is to review repair procedures or demand that these are re-cast. I'm obviously not a metalurgist. It appears my suspicions were correct. Thanks again for you help and references.

 

[arunmrao]

It is rather surprising that you have encountered these defects. Perhaps pinholes were found in DI castings. This can be due to poor Mg treatment. Cracks might be from air setting sands or high levels of S and P in the metal.

It is best advised not to review these for salvaging,but reject them right away.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke