Using bar stock for valve bodies

The opinions and experiences of using bar stock for valve bodies

Picking up on comments that bar stock might not necessarily be a bad choice for manufacturing valve bodies, Valve World editor James Hoare canvassed opinions from throughout the industry. Indeed, his appeal for insider information quickly yielded expert viewpoints from far and wide…
 
Aligning stresses

In my opinion is a good practice to align main body stresses with metal flow lines. For instance, machining a side entry ball valve body from bar stock is one thing, a globe valve body is quite another. Anyway, opinions apart, the specifications should be clearer on this topic. ASME B16.34 does not specifically preclude the use of forged bar to make a valve body, but ASTM A350 (material listed on B16.34) precludes the use of forged bar to make “flanges of all types”.

Marco Belloni, Field Service Engineer presso CARE-O-VALVE


Corrosive applications

Given a choice, I would go for bar stock valves over cast valves any day, especially if I were using these valves for corrosive applications. If I’m not wrong, some nuclear applications still insist on bar stock or forged valves and specifically prohibit cast valves. In spite of technological advances, the foundry business is, in my opinion, still a craftsman’s industry.

Kesari Prasad, Retired Chief Executive at Xomox Sanmar Ltd


Bar vs forged

I think the issue is between choosing bar against forged. Bar stock has a higher risk of porosity and flaws over forged material. There is no comparison to be made with cast.

Bernard Horsfield, Director of Technical Services at Ascendant Technologies Ltd.

Big quantities?

I have designed both cast and bar stock material bodies for valves. And it is sometimes a case by case decision. If you want to have cheap valves which are common and used in big quantities then go for cast bodies. If you need special materials or have special requirements (API) or a short lead time then (forged) bar stock is a good choice. As already mentioned there are some things to consider for the body material. For example there are two standards for stainless steel: ASTM A479 and ASTM A182. A479 is a standard bar stock specification and A182 is for forged and hot rolled bars - flanges have to be according to A182 and we are going to use this for the body also. Finally, when selecting a foundry make sure you choose a good partner.

Michael Middelbeck, Supervisor Product Engineering at Flowserve Corporation.

Erosive

Focusing strictly on quality I rarely see specifications differentiating between bar stock and forged material. I still see specifications that do not allow castings in certain grades and in corrosive or very erosive applications.

Matt Mogas, President and CEO at MOGAS Industries, Inc.

Special conditions

I agree with the other contributors that valve bodies made from bar are not necessarily bad. We have purchased such valves for Norwegian projects with different clients. Valve bodies made from bar material can be an option when delivery times are short, such as if design changes are made very late on during a project due to late design improvements. Statoil permits valve bodies made from bar on special conditions. For example, we do not accept the body / bonnet in bar for valve sizes more than 4”. Also, as the production methods for bars means that the tensile strength may be lower in the transverse direction we require additional tensile testing. Finally, the bar stock must be fully traceable with ISO EN 10204 3-1 Certificates. Comparing forgings with bars, the micro structures of forgings are stronger. Forging provides the highest quality compared to cast and bar with less chance of defects. Delivery times for forgings are longer than for bars but less than casting. Additionally, forgings are more expensive than both other alternatives of metal forming. Lastly, forgings require additional machining while castings can be very close to the final shape.

Karan Sotoodeh, Senior Piping & Valve Engineer at Aker Solutions.

Inferior structure

I noticed in the flange ASME standard that bar is allowed in lieu of forged but only up to 6”. A lot of bar has ‘A105’ for example on it but it is not! Chemically speaking it may be comparable but it is not forged and the granular structure is inferior.

Brian G Thompson, Australian Valve God-Global Supply Line & Australian Pipeline Valve


Thanks to all the respondents for sharing their thoughts.

 

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