The opinions and experiences of using bar stock for valve bodies

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

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

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