OPINION
Before ESQUIVEL, BUTTS and BAS-KIN, JJ. BUTTS, Justice.This is a venue action. Plaintiff Castilla sued defendants, Custom Tool and Machine Company and Trinity Industries, Inc., “Custom” and “Trinity” hereafter, in Bexar County, Texas, for damages, alleging personal injuries received while performing maintenance work on a rotary kiln at Barrett Industries in San Antonio.
Custom filed a plea of privilege to be sued in Gregg County, while Trinity’s plea urged transfer to Dallas County. Plaintiff filed his controverting pleas alleging proper venue to be in Bexar County under Tex. Rev.Civ.Stat.Ann. article 1995, subdivisions 9a and 23 as to Custom and subdivisions 4, 9a and 23 as to Trinity. Plaintiff did not plead subdivision 29a (Vernon 1964). The trial court overruled Custom’s plea of privilege and sustained that of Trinity and transferred the case against Trinity to Dallas County. Plaintiff timely appealed. We affirm the trial court’s order sustaining Trinity’s plea of privilege.
The agreement between the two defendant corporations was admitted into evidence at the venue hearing showing Trinity had purchased the assets of Custom in 1968. Plaintiff introduced no evidence of an agreement by Trinity to assume any outstanding tort liabilities upon transfer of ownership. The rotary kiln in question, alleged to be defective by plaintiff, was designed and sold by Custom to Barrett Industries. Trinity purchased Custom after the sale and installation by Custom but before plaintiff’s injuries which required that his hand and part of his arm be amputated.
On appeal Plaintiff argues that location of the manufacturing company is immaterial once the defective product is located in the county where the injury occurs. Although Trinity did not initially manufacture the product, plaintiff maintains that Trinity assumed all of the predecessor corporation’s liabilities, including tort liabilities. Plaintiff urges that Trinity stands in the shoes of Custom and is the successor corporation; thus venue for their case lies in Bexar County.
Plaintiff abandons subdivisions 4 and 9a of the venue statute, supra, on appeal and relies solely upon subdivision 23 which provides, in part:
“Suits against a private corporation, association, or joint stock company may be brought ... in the county in which the cause of action or part thereof arose
In order for venue to be sustainable in a county other than the domicile of the nonresident defendant corporation, under subdivision 23 it is necessary to prove a cause of action against the nonresident corporate defendant. The cause of action must be pleaded and proved by competent evidence presented at the venue hearing. Pesek v. Murrel’s Welding Works, Inc., 558 S.W.2d 39, 44 (Tex.Civ.App.—San Antonio 1977, writ dism’d w. o. j.); Santleben v. Taylor-Evans Seed Co., 585 S.W.2d 784, 786 (Tex.Civ.App.—San Antonio 1979, no writ). The cause of action must be proved by a preponderance of the evidence, and it must be the same cause of action alleged and relied on in the petition and controverting affidavit. Pesek, supra.
In cases of strict tort liability based upon defective design, as alleged here, the cause of action against the corporate manufacturer, being properly proven, arises in an action where a defectively designed product exists, causes the accident, and is a producing part of the physical harm sustained. Lubbock Manufacturing Co. v. Sames, 575 S.W.2d 588, 592 (Tex.Civ.App.—Beaumont 1978, aff’d), 598 S.W.2d 234, 236 (Tex.1980). The plaintiff here had the burden to plead and prove these venue facts: (1) The defendant was a private corporation. (2) Plaintiff had a cause of action against such *800defendant. (3) The cause of action or part thereof arose in Bexar County. See Pesek, supra. There being no findings of fact or conclusions of law in the record, it is presumed on appeal that the trial court resolved all fact issues raised by the evidence in favor of the judgment. Santleben, supra.
Examination of the venue hearing record discloses no evidence to show that Trinity assumed product liability obligation for any product manufactured by Custom. To the contrary, there was evidence that the purchase and sales agreement, accompanied by annexed contractual provisions, called Annex V, expressly addressed this point. It did provide for assumption of certain liabilities but then stated, “... provided that Trinity shall not assume any liabilities, contingent or otherwise, existing on September 30,1968 that are not set forth in said Annex V.” Plaintiff offered no evidence to refute this.
In addition, plaintiff’s argument that Trinity became the successor corporation to Custom after the purchase fails for lack of proof. In another case this burden was sustained by proving a de facto merger. See Western Resources Life Ins. Co. v. Gerhardt, 553 S.W.2d 783, 787 (Tex.Civ.App.—Austin 1977, writ ref’d n. r. e.).1 Plaintiff failed to show that Trinity is the successor corporation to Custom. We overrule plaintiff’s points of error one, two, and three.
Point of error four attacks the trial court’s order sustaining the plea of privilege and contends that the establishment of venue in Bexar County as to Custom required the joinder of Trinity as a necessary party under subdivision 29a combined with subdivision 23. Subdivision 29a provides:
Whenever there are two or more defendants in any suit brought in any county in this State and such suit is lawfully maintainable therein under the provisions of Article 1995 as to any such defendants, then such suit may be maintained in such county against any and all necessary parties thereto.
It is well established that a plaintiff who relies on subdivision 29a must allege facts which show that the defendant is a necessary party within the meaning of the statute as well as present proof of this at the venue hearing. Ladner v. Reliance Corp., 156 Tex. 158, 293 S.W.2d 758, 763-764 (1956), Tex.R.Civ.P., R. 86. Proof must show that the defendant is a necessary party and joinder is required because the plaintiff cannot otherwise obtain the complete relief to which it is entitled. Loop Cold Storage Co. v. South Texas Packers, Inc., 491 S.W.2d 106, 108 (Tex.1973).
Subdivision 29a, ancillary to subdivision 23, may have been invoked to fix venue in Bexar County had the pleadings and proof established that plaintiff was entitled to a joint judgment against the two defendant corporations in order to obtain complete relief. Ladner, supra emphasized that proof of venue facts is the price which which the plaintiff pays for the benefit he expects to derive from any exception to the rule that the defendant is entitled to be sued in his county of residence. Further plaintiff pleaded that Trinity was a “proper” party and failed to allege that subdivision 29a applied. We hold that the plaintiff has failed to establish the elements of subdivision 29a either in its pleadings or in its proof and overrule point of error four.
The order sustaining the plea of privilege is interlocutory and not appealable as to the merits of the case. Therefore, we need not speculate as to the merits, rather we leave those matters to the proper court. The judgment is affirmed.
ESQUIVEL, J., concurs in result.
. Tex.Bus.Corp.Act Ann. art. 510B (Vernon 1980), enacted after the facts in this case, provides that purchase of assets by one corporation does not cause assumption of all liabilities and obligations belonging to the selling corporation. The buyer must expressly assume them, unless required to do so by statute.