Ball Material for Valve 2

[ligin18]

Hi All
As per datasheet for pipeline ball valve(API 6D) ,the ball material is UNS S32750(SDSS). Only material grade is mentioned in datasheet. One Vendor is offering bar material(A276) for the ball but other vendor is offering forged material (A182 F53).As my understanding bar stock has a higher risk of porosity and flaws over forged material. Plz give more details for bar material Vs forged type.

 

[gerhardl]

Hi, ligin18,

I read your question as a general question on materials, to be able to evaluate if the one or other material is 'better' for your purpose than the other.

As both materials are within the technical requirements, they should both be regarded as equal satisfactory. However: quality and accuracy in production could, under circumstances, make both 'better' (less chances for faults) than the other.

My point is that there is a number of production and quality control and inspection issues that would influence the final quality of a ball more than material nomenclature. Most important would be exact geometry, quality of surface fabrication, and level and quality of material control, including certification and control of ingoing raw material before production.

 

[PeterIgg]

Ligin18,

It would also help to know the size/pressure class of the valve in question; I would assume that it is a relatively small bore if the ball can be made from bar stock? It is a moot point, balls tend not to be classed as 'pressure containing' and therefore ASTM A276 type material would normally be accepted in this application.

My biggest concern would be the heat treatment of the material. If the ball is manufactured from a hollow (cylindrical) forging then I suggest that the heat treatment of the material will produce more consistent structure through the component than would be achieved from bar stock, especially if the bar stock is heat treated (and quenched) in a bundle. These are all reasons as to why one valve will be costing significantly different amounts, which I guess has raised the question.

Whilst I would agree with your concern re defects in bar stock, most of the more susceptible parts of the material will be machined away when considering balls.

Why are you using SDSS? What is the criticality of the valve? The answers you will get to your question will vary with the responses to these, and similar, questions.

 

[ligin18]

Hi Peter
The service is produced water around 143K of chloride content.So the material for the trim is selected as SDSS with Carbon steel body(6mm CA).The valve size is 16" (full bore) design for 150#.The inspection level is II.

 

[PeterIgg]

Ligin18
Sorry for the delay. Personally, and I stand to be corrected here, I would be suspicious of SDSS bar that is in the order of 24" in diameter having suitable heat treatment throughout the bar. From that standpoint I would go with a forged component, specifically one that is forged as close as practical to the final shape (viz a hollow cylinder). Otherwise I would be looking for tests on the material itself at about the 1/4 t position close to the middle (lengthwise) of the bar, specifically looking for metallographic tests for the structure and mechanical/impact tests.

Being a 16" NB valve it will have to be trunnion mounted. Therefore the seats will be energised in the seat pocket (spring loaded), therefore the seat will have to seal against the body material. Therefore I trust that you have a CRA overlay in the seal areas for the seat, stem and body joint. 6 mm of corrosion allowance is irrelevant if all the seals are not functioning correctly.