Corrosion resistant isolator

• US 5,230,248 A
• Filed: 08/14/1992
• Issued: 07/27/1993
• Est. Priority Date: 07/12/1991
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Cucci, Gerald R., Lemire, Steven M.
• Primary Examiner(s): WOODIEL, DONALD
• Application Number:
  US07/930,844
• Time in Patent Office: 347 Days
• Field of Search: 73/706, 73/715-728, 73/756, 73/278, 73/98 R, 92/103 M, 228/107, 228/108, 228/178, 228/101
• US Class Current: 73/706
• CPC Class Codes: G01L 19/0046 using isolation membranes G01L13/026 and G01L19/0645 take precedence
• CPC Class Codes: G01L 19/0645 using isolation membranes, specially adapted for protection
• CPC Class Codes: G01L 9/0044 Constructional details of non-semiconductive diaphragms

Abstract

An isolator for use in pressure transmitters for isolating the process fluid being sensed from a sensor, comprises an isolating diaphragm that is thin, and made of a suitable corrosion resistant metal, such as tantalum, and which must be anchored to an isolator housing made of a substantially different metal such as stainless steel. Tantalum is very resistant to corrosion, and is a high melting point metal, which is substantially higher than the material comprising the sensor housing so direct welding is virtually impossible. The present invention relates to securing a support ring of the same metal as the diaphragm surrounding the cavity formed for the isolator fluid, preforming a thin metal diaphragm made of the selected material, and then welding the diaphragm and a ring overlying the diaphragm directly to the support ring. Using a support ring that is separately secured in place on the isolator body permits the welding temperature to be raised sufficiently for fastening the high melting point components (tantalum) together without damaging the sensor housing.

Claims

1. A pressure isolator comprising a body made of a first metallic material defining a cavity, a thin flexible diaphragm made of a second metallic material not compatible with direct welding to the first metallic material, a one-piece support ring made entirely of the same material as the diaphragm mounted directly to said body surrounding an isolator opening, and an annular peripheral weld sealing and joining the support ring and the diaphragm together around the periphery of the diaphragm to provide a sealed cavity relative to the body and the isolator opening.

2. The pressure isolator of claim 1 wherein said support ring is brazed to the body.

3. The pressure isolator of claim 1 and a support surface on said body comprising an annular recess, and said support ring being fitted within said recess and brazed to the body.

4. The pressure isolator of claim 1 and an annular weld ring forming an annular cavity overlying the diaphragm, and being made of the same material as the diaphragm and the support ring, said weld ring having a base wall through which the annular peripheral weld passes, and said weld also passing through the diaphragm and into the support ring.

5. The pressure isolator as specified in claim 4 wherein the first metallic material has a melting temperature which is incompatible for direct welding with a melting temperature of the second metallic material.

6. The pressure isolator as specified in claim 5 wherein said support ring, said diaphragm and said weld ring are made of tantalum.

7. The pressure isolator of claim 1, wherein said support ring is sealingly engaged to the body along the periphery of the diaphragm.

8. A method of mounting a high melting point diaphragm onto a body of substantially lower melting point material defining a cavity comprising the steps of:

`providing an isolator region on the body;

securing a one-piece ring made entirely of the same material as the diaphragm directly to the body surrounding the isolator region; and

welding the diaphragm to the support ring with a continuous annular fluid-tight weld.

9. The method of claim 8 including the further step of providing an overlying weld ring over the diaphragm on a side opposite the support ring, and welding through the weld ring, the diaphragm and into the support ring for providing the fluid-tight annular weld around the diaphragm to seal the diaphragm.

10. The method of claim 9 including the step of forming the diaphragm to a corrugated shape.

11. The method of claim 8 wherein said securing step comprising brazing the support ring to a support surface on the body.

12. The method of claim 8 includes the step of forming an annular groove on the body surrounding a depression defining the isolator region, and the securing step comprises brazing the support ring into the groove prior to welding the diaphragm to the support ring.

13. The method of claim 9 including the step of selecting the diaphragm, support ring and weld ring to be of tantalum.

14. The method of claim 13 including selecting the body material to be 316L Stainless Steel.

15. The method of claim 13 including selecting the body material to be 17-4 ph stainless steel.

16. The method of claim 8 and machining the support ring after securing the support ring to the body.