Format: 

Agency. (Year, Month). Title of standard (Standard No. 123). Available from URL

Author, A. A. (Year, Month). Title of standard (Standard No. 123). Location: Publishing Agency.

Examples: 

ASTM. (2015, March). Standard test methods for quantitative analysis of textiles (Standard No. D629 - 15). Available from http://www.astm.org

In-text: (ASTM, 2015, para. 15)

Notes: 

For standards available for purchase include "Available from" and a URL to the distributor's website. If no website is available, include the distributor's name, full address and zip code in parentheses at the end of the citation.

Source:

This source type is not covered by the APA style guidelines.
Example(s) adapted from:
APA (ER): no. 28